100 atoms of Neon contains 882 atoms of 2210 Ne isotopes Therefore


RAM of Neon  9092100 x20  026100 x 21 882 100 x 22


Note that


Relative atomic mass has no units


More atoms of Neon exist as 2010Ne 9092 therefore RAM is nearer to the more abundant 2010Ne isotope


Calculate the relative atomic mass of Argon given that it exist as


9092 2010Ne  026 2110Ne  882 2210Ne


NB


The relative atomic mass is a measure of the masses of atoms The higher the relative atomic mass the heavier the atom


Electrons are found in energy levelsorbital


An energy level is a fixed region aroundsurrounding the nucleus of an atom occupied by electrons of the same potential energy


By convention energy levels are named 123 outwards from the region nearest to nucleus


Each energy level is occupied by a fixed number of electrons


The 1st energy level is occupied by a maximum of two electrons


The 2nd energy level is occupied by a maximum of eight electrons


The 3rd energy level is occupied by a maximum of eight electrons or eighteen electrons if available


The 4th energy level is occupied by a maximum of eight electrons or eighteen or thirty two electrons if available


This arrangement of electrons in an atom is called electron configuration  structure


By convention the electron configuration  structure of an atom of an element can be shown in form of a diagram using either crossx or dot to


Practice examples drawing electronic configurations


a11H has  in nucleus1proton and 0 neutrons


1 electron in the 1st energy levels thus


Nucleus


Energy levels


Electrons represented by crossx


Electronic structure of Hydrogen is thus 1


b 42He has  in nucleus 2 proton and 2 neutrons


2 electron in the 1st energy levels thus


Electronic structure of Helium is thus 2


c 73Li has  in nucleus 3 proton and 4 neutrons


2 electron in the 1st energy levels


1 electron in the 2nd energy levels thus


Electronic structure of Lithium is thus 21


d 94Be has  in nucleus 4 proton and 5 neutrons


2 electron in the 2nd energy levels thus


Electronic structure of Beryllium is thus 22


e 115B has  in nucleus 5 proton and 6 neutrons


3 electron in the 2nd energy levels thus


Electronic structure of Boron is thus 23


f 126C has  in nucleus 6 proton and 6 neutrons


4 electron in the 2nd energy levels thus


Nucleus


Energy levels


Electrons represented by crossx


Electronic structure of Carbon is thus 24


g 147N has  in nucleus 7 proton and 7 neutrons


5 electron in the 2nd energy levels thus


Electronic structure of Nitrogen is thus 25


h 168O has  in nucleus 8 proton and 8 neutrons


2 electron in the 1st energy levels


6 electron in the 2nd energy levels thus


Electronic structure of Oxygen is thus 26


i 199F has  in nucleus 9 proton and 10 neutrons


7 electron in the 2nd energy levels thus


Electronic structure of Fluorine is thus 27


i 2010Ne has  in nucleus 10 proton and 10 neutrons


8 electron in the 2nd energy levels thus


Electronic structure of Neon is thus 28


j 2311Na has  in nucleus 11 proton and 12 neutrons


8 electron in the 2nd energy levels


1 electron in the 3rd energy levels thus


Nucleus


Energy levels


Electrons represented by dot


Electronic structure of Sodium is thus 281


k 2412Mg has  in nucleus 12 proton and 12 neutrons


2 electron in the 1st energy levels


2 electron in the 3rd energy levels thus


Electronic structure of Magnesium is thus 282


l 2713Al has  in nucleus 13 proton and 14 neutrons


3 electron in the 3rd energy levels thus


Electronic structure of Aluminium is thus 283


m 2814Si has  in nucleus 14 proton and 14 neutrons


4 electron in the 3rd energy levels thus


Electronic structure of Silicon is thus 284


n 3115P has  in nucleus 14 proton and 15 neutrons


8 electron in the 2nd energy levels


5 electron in the 3rd energy levels thus


Nucleus


Energy levels


Electrons represented by dot


Electronic structure of Phosphorus is thus 285


o 3216S has  in nucleus 16 proton and 16 neutrons


2 electron in the 1st energy levels


6 electron in the 3rd energy levels thus


Electronic structure of Sulphur is thus 286


p 3517Cl has  in nucleus 18 proton and 17 neutrons


7 electron in the 3rd energy levels thus


Electronic structure of Chlorine is thus 287


p 4018Ar has  in nucleus 22 proton and 18 neutrons


8 electron in the 3rd energy levels thus


Electronic structure of Argon is thus 288


q 3919K has  in nucleus 20 proton and 19 neutrons


8 electron in the 2nd energy levels


8 electron in the 3rd energy levels


1 electron in the 4th energy levels thus


Nucleus


Energy levels


Electrons represented by dot


Electronic structure of Potassium is thus 2881


r 4020Ca has  in nucleus 20 proton and 20 neutrons


2 electron in the 1st energy levels


2 electron in the 4th energy levels thus


Electronic structure of Calcium is thus 2882


BPERIODIC TABLE


There are over 100 elements so far discovered Scientists have tried to group them together in a periodic table


A periodic table is a horizontal and vertical arrangement of elements according to their atomic numbers


This table was successfully arranged in 1913 by the British scientist Henry Moseley from the previous work of the Russian Scientist Dmitri Mendeleev


The horizontal arrangement forms period Atoms in the same period have the same the same number of energy levels in their electronic structure ie


The number of energy levels in the electronic configuration of an element determine the period to which the element is in the periodic table


eg


Which period of the periodic table are the following isotopeselementsatoms


Electron structure 24  2 energy levels used thus Period 2


Electron structure 281  3 energy levels used thus Period 3


Electron structure 2881  4 energy levels used thus Period 4


Electron structure 1  1 energy level used thus Period 1


The vertical arrangement of elements forms a group Atoms in the same have the same the same group have the same number of outer energy level electrons as per their electronic structure ie


The number of electrons in the outer energy level an element determine the group to which the element is in the periodic table


Electron structure 24  4 electrons in outer energy level thus Group IV


Electron structure 281  1 electron in outer energy level thus Group I


Electron structure 28811 electron in outer energy level thus Group I


Electron structure 1  1 electron in outer energy level thus Group I


By convention


iPeriods are named using English numerals 1 2 3 4


iiGroups are named using Roman numerals I II III IV


There are eighteen groups in a standard periodic table


There are seven periods in a standard periodic table


When an atom has maximum number of electrons in its outer energy level it is said to be stable


When an atom has no maximum number of electrons in its outer energy level it is said to be unstable


All stable atoms are in group 818 of the periodic table All other elements are unstable


All unstable atomsisotopes try to be stable through chemical reactions A chemical reaction involves gaining or losing outer electrons electron transfer When electron transfer take place an ion is formed


An ion is formed when an unstable atom gain or donate electrons in its outer energy level in order to be stable Whether an atom gain or donate electrons depend on the relative energy required to donate or gain extra electrons ie


Examples


199 F has electronic structureconfiguration 27


It can donate the seven outer electrons to have stable electronic structureconfiguration 2


It can gain one extra electron to have stable electronic structureconfiguration 28 Gaining requires less energy and thus Fluorine reacts by gaining one extra electrons


2313 Al has electronic structureconfiguration 283


It can donate the three outer electrons to have stable electronic structureconfiguration 28


It can gain five extra electrons to have stable electronic structureconfiguration 288 Donating requires less energy and thus Aluminium reacts by donating its three outer electrons


Elements with less than four electrons in the outer energy level donates lose the outer electrons to be stable and form a positively charged ion called cation


A cation therefore has more protons positive charge than electrons negative charge


Generally metals usually form cation


Elements with more than four electrons in the outer energy level gain acquire extra electrons in the outer energy level to be stable and form a negatively charged ion called anion


An anion therefore has fewer protons positive charge than electrons negative charge


Generally non metals usually form anion Except Hydrogen


The charge carried by an ion is equal to the number of electrons gainedacquired or donatedlost


Examples of ion formation


H  H  e


atom monovalent cation electrons donatedlost


Electronic configuration 1 No electrons remains


2 2713 Al


Al  Al3  3e


atom trivalent cation 3 electrons donatedlost


Electron 283 28


structure unstable stable


3 2311 Na


Na  Na  e


atom cation  1 electrons donatedlost


Electron 281 28


4 2412Mg


Mg  Mg2  2e


atom cation  2 electrons donatedlost


5 168O


O  2e  O2


atom  2 electrons gainedacquired anion


Electron 26 28


6 147N


N  3e  N3


atom  3 electrons gainedacquired anion


Electron 25 28


7 3115P


P  3e  P3


structure unstable stable


8 199F


F  e  F


atom  1 electrons gainedacquired anion


Electron 27 28


9 3517Cl


Cl  e  Cl


Electron 287 288


3 3919 K


K  K  e


atom cation  1 electrons donatedlost


Electron 2881 288


When an element donatesloses its outer electrons the process is called oxidation When an element acquiresgains extra electrons in its outer energy level the process is called reduction The charge carried by an atom cation or anion is its oxidation state


Table showing the oxidation states of some isotopes


Note


Some elements can exist in more than one oxidation state They are said to have variable oxidation state


Roman capital numeral is used to indicate the oxidation state of an element with a variable oxidation state in a compound


Examples


Copper I means Cu as in CopperIoxide


Copper II means Cu2 as in CopperIIoxide


Iron II means Fe2 as in IronIIsulphide


iv Iron III means Fe3 as in IronIIIchloride


SulphurVImean S6 as in IronIIIsulphateVI


SulphurVImean S6 as in sulphurVIoxide


SulphurIVmean S4 as in sulphurIVoxide


SulphurIVmean S4 as in sodium sulphateIV


ix CarbonIVmean C4 as in carbonIVoxide


x CarbonIVmean C4 as in LeadIIcarbonateIV


xi CarbonIImean C2 as in carbonIIoxide


xii ManganeseIVmean Mn4 as in ManganeseIVoxide


A compound is a combination of two or more elements in fixed proportions The ratio of the atoms making a compound is called the chemical formulae Elements combine together to form a compound depending on their combining power


The combining power of atoms in an element is called Valency Valency of an element is equal to the number of


i Hydrogen atoms that an atom of element can combine with or displace


ii Electrons gained acquired in outer energy level by non metals to be stableattain dupletoctet


iii Electrons donatedlost by outer energy level of metals to be stableattain octetduplet


iv Charges carried by ionscationsions


Group of atoms that react as a unit during chemical reactions are called radicals Elements with variable oxidation state also have more than one valency


Table showing the valency of common radicals


Table showing the valency of some common metal and non metals


From the valency of elements the chemical formular of a compound can be derived using the following procedure


iIdentify the elements and radicals making the compound


iiWrite the symbolformular of the elements making the compound starting with the metallic element


iiiAssign the valency of each element radical as superscript


ivInterchangeexchange the valencies of each element as subscript


vDivide by the smallestlowest valency to derive the smallest whole number ratios


Ignore a valency of 1


This is the chemical formula


Practice examples


Write the chemical formula of


aAluminium oxide


Chemical formula of Aluminium oxide is thus Al2 O3


This means 2atoms of Aluminium combine with 3 atoms of Oxygen


bSodium oxide


Chemical formula of Sodium oxide is thus Na2 O


This means 2atoms of Sodium combine with 1 atom of Oxygen


cCalcium oxide


Chemical formula of Calcium oxide is thus CaO


This means 1 atom of calcium combine with 1 atom of Oxygen


dLead IV oxide


Chemical formula of Lead IV oxide is thus PbO2


This means 1 atom of lead combine with 2 atoms of Oxygen


eLead II oxide


Chemical formula of Lead II oxide is thus PbO


This means 1 atom of lead combine with 1 atom of Oxygen


eIron III oxide


Chemical formula of IronIII oxide is thus Fe2O3


This means 2 atom of lead combine with 3 atom of Oxygen


fIron II sulphate VI


Chemical formula of Iron II sulphate VI is thus FeSO4


This means 1 atom of Iron combine with 1 sulphate VI radical


gCopper II sulphate VI


Chemical formula of CuIIsulphateVI is thus CuSO4


This means 1 atom of Copper combine with 1 sulphate VI radical


hAluminium sulphate VI


Chemical formula of Aluminium sulphate VI is thus Al2SO43


This means 2 atom of Aluminium combine with 3 sulphate VI radical


iAluminium nitrate V


Chemical formula of Aluminium sulphate VI is thus Al NO33


This means 1 atom of Aluminium combine with 3 nitrate V radical


jPotassium manganate VII


Chemical formula of Potassium manganate VII is thus KMnO4


This means 1 atom of Potassium combine with 4 manganate VII radical


kSodium dichromate VI


Chemical formula of Sodium dichromate VI is thus Na2 Cr2O7


This means 2 atom of Sodium combine with 1 dichromate VI radical


lCalcium hydrogen carbonate


Chemical formula of Calcium hydrogen carbonate is thus Ca HCO32


This means 1 atom of Calcium combine with 2 hydrogen carbonate radical


lMagnesium hydrogen sulphate VI


Chemical formula of Magnesium hydrogen sulphate VI is thus Mg HSO42


This means 1 atom of Magnesium combine with 2 hydrogen sulphate VI radical


Compounds are formed from chemical reactions A chemical reaction is formed when atoms of the reactants break free to bond again and form products A chemical reaction is a statement showing the movement of reactants to form products The following procedure is used in writing chemical equations


1 Write the word equation


2 Write the correct chemical formula for each of the reactants and products


3 Check if the number of atoms of each element on the reactant side is equal to the number of atoms of each element on the product side


4 Multiply the chemical formula containing the unbalanced atoms with the lowest common multiple if the number of atoms on one side is not equal This is called balancing


Do not change the chemical formula of the productsreactants


5 Assign in brackets the physical statestate symbols of the reactants and products after each chemical formula as


i s for solids


ii l for liquids


iii g for gas


iv aq for aqueousdissolved in water to make a solution


Practice examples


Write a balanced chemical equation for the following


Hydrogen gas is prepared from reacting Zinc granules with dilute hydrochloric acid


Procedure


Zinc  Hydrochloric acid  Zinc chloride  hydrogen gas


Zn  HCl  ZnCl2  H2


Number of atoms of Zn on the reactant side is equal to product side


One atom of H in HCl on the reactant side is not equal to two atoms in H2 on product side


One atom of Cl in HCl on the reactant side is not equal to two atoms in ZnCl2 on product side


4 Multiply the chemical formula containing the unbalanced atoms with the lowest common multiple if the number of atoms on one side is not equal


Multiply HCl by 2 to get 2 Hydrogen and 2 Chlorine on product and reactant side


Zn  2 HCl  ZnCl2  H2


5 Assign in brackets the physical statestate symbols


Zns  2 HClaq  ZnCl2 aq  H2g


Oxygen gas is prepared from decomposition of Hydrogen peroxide solution to water


1 Write the word equation


Hydrogen peroxide  Water  oxygen gas


H2O2  H2O  O2


Number of atoms of H on the reactant side is equal to product side


Two atom of O in H2O2 on the reactant side is not equal to three atoms one in H2O and two in O2 on product side


Multiply H2O2 by 2 to get 4 Hydrogen and 4 Oxygen on reactants


Multiply H2O by 2 to get 4 Hydrogen and 2 Oxygen on product side


When the 2 Oxygen in O2 and the2 in H2O are added on product side they are equal to the4 Oxygen on reactants side


2H2O2  2H2O  O2


2H2O2aq  2H2Ol  O2g


Chlorine gas is prepared from Potassium manganate VII reacting with hydrochloric acid to form potassium chloride solution manganese II chloride solution water and chlorine gas


Procedure


Potassium manganate VII  Hydrochloric acid


Potassium chloride  manganese II chloride  chlorine water


2 Write the correct chemical formula for each of the reactants and products


KMnO4  HCl  KCl  MnCl2 H2O  Cl2


3 Check if the number of atoms of each element on the reactant side is equal to the number of atoms of each element on the product side


Number of atoms of K and Mn on the reactant side is equal to product side


Two atom of H in H2O on the product side is not equal to one atom on reactant side


Four atom of O in KMnO4 is not equal to one in H2O


One atom of Cl in HCl on reactant side is not equal to three one in H2O and two in Cl2


4 Multiply the chemical formula containing the unbalanced atoms with the lowest common multiple if the number of atoms on one side is not equal


Multiply HCl by 16 to get 16 Hydrogen and 16 Chlorine on reactants


Multiply KMnO4 by 2 to get 2 Potassium and 2 manganese 2 x4 8 Oxygen on reactant side


Balance the product side to get


2 KMnO4 16 HCl  2 KCl  2 MnCl2 8 H2O  5 Cl2


5 Assign in brackets the physical statestate symbols


2KMnO4s 16 HClaq 2 KCl aq  2MnCl2aq8 H2Ol5 Cl2g


dCarbon IV oxide gas is prepared from Calcium carbonate reacting with hydrochloric acid to form calcium chloride solution water and carbon IV oxide gas


Procedure


1 Write the word equation


Calcium carbonate  Hydrochloric acid


Calcium chloride solution water carbon IVoxide


CaCO3  HCl  CaCl2 H2O  CO2


CaCO3s  2 HClaq  CaCl2aq  H2Ol  CO2g


dSodium hydroxide solution neutralizes hydrochloric acid to form salt and water


NaOHaq  HClaq  NaCl aq  H2Ol


eSodium reacts with water to form sodium hydroxide and hydrogen gas


2Nas  2H2Ol  2NaOHaq  H2g


fCalcium reacts with water to form calcium hydroxide and hydrogen gas


Cas  2H2Ol  CaOH2aq  H2g


gCopper II Oxide solid reacts with dilute hydrochloric acid to form copper II chloride and water


CuOs  2HClaq  CuCl2aq  H2Ol


hHydrogen sulphide reacts with Oxygen to form sulphur IV Oxide and water


2H2Sg  3O2g  2SO2g  2H2Ol


iMagnesium reacts with steam to form Magnesium Oxide and Hydrogen gas


Mgs  2H2Og  MgOs  H2g


jEthane C2H6 gas burns in air to form Carbon IV Oxide and water


2C2H6g  7O2g  4CO2g  6H2Ol


kEthene C2H4 gas burns in air to form Carbon IV Oxide and water


C2H4g  3O2g  2CO2g  2H2Ol


lEthyne C2H2 gas burns in air to form Carbon IV Oxide and water


2C2H2g  5O2g  4CO2g  2H2Ol


C PERIODICITY OF CHEMICAL FAMILESDOWN THE GROUP


The number of valence electrons and the number of occupied energy levels in an atom of an element determine the position of an element in the periodic table ie


The number of occupied energy levels determines the Period and the valence electrons determine the Group


Elements in the same group have similar physical and chemical properties The trends in physical and chemical properties of elements in the same group vary down the group Elements in the same group thus constitute a chemical family


Group I elements Alkali metals


Group I elements are called Alkali metals except Hydrogen which is a non metal The alkali metals include


All alkali metals atom has one electron in the outer energy level They therefore are monovalent They donate lose the outer electron to have oxidation state M


The number of energy levels increases down the group from Lithium to Francium The more the number of energy levels the biggerlarger the atomic size eg


The atomic size of Potassium is biggerlarger than that of sodium because Potassium has more4 energy levels than sodium 3 energy levels


Atomic and ionic radius


The distance between the centre of the nucleus of an atom and the outermost energy level occupied by electrons is called atomic radius Atomic radius is measured in nanometersnThe higher bigger the atomic radius the bigger larger the atomic size


The distance between the centre of the nucleus of an ion and the outermost energy level occupied by electrons is called ionic radius Ionic radius is also measured in nanometers nThe higher bigger the ionic radius the bigger larger the size of the ion


Atomic radius and ionic radius depend on the number of energy levels occupied by electrons The more the number of energy levels the biggerlarger the atomic ionic radius eg


The atomic radius of Francium is biggerlarger than that of sodium because Francium has more7 energy levels than sodium 3 energy levels


Atomic radius and ionic radius of alkali metals increase down the group as the number of energy levels increases


The atomic radius of alkali metals is bigger than the ionic radius This is because alkali metals react by losingdonating the outer electron and hence lose the outer energy level


Table showing the atomic and ionic radius of some alkali metals


The atomic radius of sodium is 0157nM The ionic radius of Na is 0095nM This is because sodium reacts by donatinglosing the outer electrons and hence the outer energy level The remaining electronsenergy levels experience more effective  greater nuclear attractionpull towards the nucleus reducing the atomic radius


Electropositivity


The ease of donatinglosing electrons is called electropositivity All alkali metals are electropositive Electropositivity increase as atomic radius increase This is because the effective nuclear attraction on outer electrons decreases with increase in atomic radius The outer electrons experience less nuclear attraction and can be lost donated easilywith ease Francium is the most electropositive element in the periodic table because it has the highestbiggest atomic radius


Ionization energy


The minimum amount of energy required to remove an electron from an atom of element in its gaseous state is called 1st ionization energy The SI unit of ionization energy is kilojoules per molekJmole1 Ionization energy depend on atomic radius The higher the atomic radius the less effective the nuclear attraction on outer electronsenergy level and thus the lower the ionization energy For alkali metals the 1st ionization energy decrease down the group as the atomic radius increase and the effective nuclear attraction on outer energy level electrons decrease


eg The 1st ionization energy of sodium is 496 kJmole1 while that of potassium is 419 kJmole1 This is because atomic radius increase and thus effective nuclear attraction on outer energy level electrons decrease down the group from sodium to Potassium It requires therefore less energy to donatelose outer electrons in Potassium than in sodium


Physical properties


SoftEasy to cut Alkali metals are soft and easy to cut with a knife The softness and ease of cutting increase down the group from Lithium to Francium This is because an increase in atomic radius decreases the strength of metallic bond and the packing of the metallic structure


Appearance Alkali metals have a shiny grey metallic luster when freshly cut The surface rapidlyquickly tarnishes on exposure to air This is because the metal surface rapidlyquickly reacts with elements of airoxygen


Melting and boiling points Alkali metals have a relatively low meltingboiling point than common metals like Iron This is because alkali metals use only one delocalized electron to form a weak metallic bondstructure


Electricalthermal conductivity Alkali metals are good thermal and electrical conductors Metals conduct using the outer mobile delocalized electrons The delocalized electrons move randomly within the metallic structure


Summary of some physical properties of the 1st three alkali metals


Chemical properties


iReaction with airoxygen


On exposure to air alkali metals react with the elements in the air


Example


On exposure to air Sodium first reacts with Oxygen to form sodium oxide


4Nas  O2g  2Na2Os


The sodium oxide formed further reacts with watermoisture in the air to form sodium hydroxide solution


Na2Os  H2Ol  2NaOHaq


Sodium hydroxide solution reacts with carbon IV oxide in the air to form sodium carbonate


2NaOH aq  CO2 g  Na2CO3 g  H2O l


iiBurning in airoxygen


Lithium burns in air with a crimsondeep red flame to form Lithium oxide


4Li s  O2 g  2Li2Os


Sodium burns in air with a yellow flame to form sodium oxide


4Na s  O2 g  2Na2Os


Sodium burns in oxygen with a yellow flame to form sodium peroxide


2Na s  O2 g  Na2O2 s


Potassium burns in air with a lilacpurple flame to form potassium oxide


4K s  O2 g  2K2O s


iii Reaction with water


Experiment


Measure 500 cm3 of water into a beaker


Put three drops of phenolphthalein indicator


Put about 05g of Lithium metal into the beaker


Determine the pH of final product


Repeat the experiment using about 01 g of Sodium and Potassium


Caution Keep a distance


Observations


Explanation


Alkali metals are less dense than water They therefore float in water They react with water to form a strongly alkaline solution of their hydroxides and producing hydrogen gas The rate of this reaction increase down the group ie Potassium is more reactive than sodium Sodium is more reactive than Lithium


The reactivity increases as electropositivity increases of the alkali increases This is because as the atomic radius increases the ease of donatinglosing outer electron increases during chemical reactions


Chemical equations


2Lis  2H2Ol  2LiOHaq  H2g


2Nas  2H2Ol  2NaOHaq  H2g


2Ks  2H2Ol  2KOHaq  H2g


2Rbs  2H2Ol  2RbOHaq  H2g


2Css  2H2Ol  2CsOHaq  H2g


2Frs  2H2Ol  2FrOHaq  H2g


Reactivity increase down the group


iv Reaction with chlorine


Experiment


Cut about 05g of sodium into a deflagrating spoon with a lid cover Introduce it on a Bunsen flame until it catches fire Quickly and carefully lower it into a gas jar containing dry chlorine to cover the gas jar


Repeat with about 05g of Lithium


Caution This experiment should be done in fume chamber because chlorine is poisonous toxic


Observation


Sodium metal continues to burn with a yellow flame forming white solidfumes


Lithium metal continues to burn with a crimson flame forming white solid  fumes


Alkali metals react with chlorine gas to form the corresponding metal chlorides The reactivity increase as electropositivity increase down the group from Lithium to Francium The ease of donatinglosing the outer electrons increase as the atomic radius increase and the outer electron is less attracted to the nucleus


Chemical equations


2Lis  Cl2g  2LiCls


2Nas  Cl2g  2NaCls


2Ks  Cl2g  2KCls


2Rbs  Cl2g  2RbCls


2Css  Cl2g  2CsCls


2Frs  Cl2g  2FrCls Reactivity increase down the group


The table below shows some compounds of the 1st three alkali metals


Some uses of alkali metals include


iSodium is used in making sodium cyanide for extracting gold from gold ore


iiSodium chloride is used in seasoning food


iiiMolten mixture of sodium and potassium is used as coolant in nuclear reactors


ivSodium is used in making sodium hydroxide used in making soapy and soapless detergents


vSodium is used as a reducing agent for the extraction of titanium from Titanium IV chloride


viLithium is used in making special high strength glasses


viiLithium compounds are used to make dry cells in mobile phones and computer laptops


Group II elements Alkaline earth metals


Group II elements are called Alkaline earth metals  The alkaline earth metals include


All alkaline earth metal atoms have two electrons in the outer energy level They therefore are divalent They donate lose the two outer electrons to have oxidation state M2


The number of energy levels increases down the group from Beryllium to Radium The more the number of energy levels the biggerlarger the atomic size eg


The atomic sizeradius of Calcium is biggerlarger than that of Magnesium because Calcium has more4 energy levels than Magnesium 3 energy levels


Atomic radius and ionic radius of alkaline earth metals increase down the group as the number of energy levels increases


The atomic radius of alkaline earth metals is bigger than the ionic radius This is because they react by losingdonating the two outer electrons and hence lose the outer energy level


Table showing the atomic and ionic radius of the 1st three alkaline earth metals


The atomic radius of Magnesium is 0136nM The ionic radius of Mg2 is 0065nM This is because Magnesium reacts by donatinglosing the two outer electrons and hence the outer energy level The remaining electronsenergy levels experience more effective  greater nuclear attractionpull towards the nucleus reducing the atomic radius


Electropositivity


All alkaline earth metals are also electropositive like alkali metals The electropositivity increase with increase in atomic radiussize Calcium is more electropositive than Magnesium This is because the effective nuclear attraction on outer electrons decreases with increase in atomic radius The two outer electrons in calcium experience less nuclear attraction and can be lost donated easilywith ease because of the higherbigger atomic radius


Ionization energy


For alkaline earth metals the 1st ionization energy decrease down the group as the atomic radius increase and the effective nuclear attraction on outer energy level electrons decrease eg The 1st ionization energy of Magnesium is 900 kJmole1 while that of Calcium is 590 kJmole1 This is because atomic radius increase and thus effective nuclear attraction on outer energy level electrons decrease down the group from magnesium to calcium


It requires therefore less energy to donatelose outer electron in calcium than in magnesium


The minimum amount of energy required to remove a second electron from an ion of an element in its gaseous state is called the 2nd ionization energy


The 2nd ionization energy is always higher bigger than the 1st ionization energy


This is because once an electron is donated lost form an atom the overall effective nuclear attraction on the remaining electronsenergy level increase Removing a second electron from the ion require therefore more energy than the first electron


The atomic radius of alkali metals is higherbigger than that of alkaline earth metals This is because acrossalong the period from left to right there is an increase in nuclear charge from additional number of protons and still additional number of electrons entering the same energy level Increase in nuclear charge increases the effective nuclear attraction on the outer energy level which pulls it closer to the nucleus eg


Atomic radius of Sodium 0157nM is higher than that of Magnesium 0137nM This is because Magnesium has more effective nuclear attraction on the outer energy level than Sodium hence pulls outer energy level more nearer to its nucleus


Physical properties


SoftEasy to cut Alkaline earth metals are not soft and easy to cut with a knife like alkali metals This is because of the decrease in atomic radius of corresponding alkaline earth metal increases the strength of metallic bond and the packing of the metallic structure Alkaline earth metals are


ductileable to form wirethin long rods


malleableable to be hammered into sheetlong thin plates


have high tensile strengthable to be coiled without breaking not brittlewithstand stress


Appearance Alkali earth metals have a shiny grey metallic luster when their surface is freshly polished scrubbed The surface slowly tarnishes on exposure to air This is because the metal surface slowly undergoes oxidation to form an oxide This oxide layer should be removed before using the alkaline earth metals


Melting and boiling points Alkaline earth metals have a relatively high melting boiling point than alkali metals This is because alkali metals use only one delocalized electron to form a weaker metallic bondstructure Alkaline earth metals use two delocalized electrons to form a stronger metallic bond structure


The melting and boiling points decrease down the group as the atomic radiussize increase reducing the strength of metallic bond and packing of the metallic structure eg


Beryllium has a melting point of 1280oC Magnesium has a melting point of 650oCBeryllium has a smaller atomic radiussize than magnesium The strength of metallic bond and packing of the metallic structure is thus stronger in beryllium


Electricalthermal conductivity Alkaline earth metals are good thermal and electrical conductors The two delocalized valence electrons move randomly within the metallic structure


Electrical conductivity increase down the group as the atomic radiussize increase making the delocalized outer electrons less attracted to nucleus Alkaline earth metals are better thermal and electrical conductors than alkali metals because they have moretwo outer delocalized electrons eg


Magnesium is a better conductor than sodium because it has moretwo delocalized electrons than sodium The more delocalized electrons the better the electrical conductor


Calcium is a better conductor than magnesium


Calcium has biggerlarger atomic radius than magnesium because the delocalized electrons are less attracted to the nucleus of calcium and thus more free mobile and thus better the electrical conductor


Summary of some physical properties of the 1st three alkaline earth metals


Chemical properties


Reaction with airoxygen


On exposure to air the surface of alkaline earth metals is slowly oxidized to its oxide on prolonged exposure to air


Example


On exposure to air the surface of magnesium ribbon is oxidized to form a thin film of Magnesium oxide


2Mgs  O2g  2MgOs


ii Burning in airoxygen


Experiment


Hold a about 2cm length of Magnesium ribbon on a Bunsen flame Stop heating when it catches firestart burning


Caution Do not look directly at the flame


Put the products of burning into 100cm3 beaker Add about 5cm3 of distilled water Swirl Test the mixture using litmus papers Repeat with Calcium


Observations


Magnesium burns with a bright blindening flame


White solid ash produced


Solid dissolves in water to form a colourless solution


Blue litmus paper remain blue


Red litmus paper turns blue


colourless gas with pungent smell of urine


Explanation


Magnesium burns in air with a bright blindening flame to form a mixture of Magnesium oxide and Magnesium nitride


2Mg s  O2 g  2MgOs


3Mg s  N2 g  Mg3N2 s


Magnesium oxide dissolves in water to form magnesium hydroxide


MgOs  H2O l  Mg OH2aq


Magnesium nitride dissolves in water to form magnesium hydroxide and produce ammonia gas


Mg3N2 s  6H2O l  3Mg OH2aq  2NH3 g


Magnesium hydroxide and ammonia are weakly alkaline with pH 891011 and turns red litmus paper blue


Calcium burns in air with faint orangered flame to form a mixture of both Calcium oxide and calcium nitride


2Ca s  O2 g  2CaOs


3Ca s  N2 g  Ca3N2 s


Calcium oxide dissolves in water to form calcium hydroxide


CaOs  H2O l  Ca OH2aq


Calcium nitride dissolves in water to form calcium hydroxide and produce ammonia gas


Ca3N2 s  6H2O l  3Ca OH2aq  2NH3 g


Calcium hydroxide is also weakly alkaline solution with pH 891011 and turns red litmus paper blue


Reaction with water


Experiment


Measure 50 cm3 of distilled water into a beaker


Scrubpolish with sand paper 1cm length of Magnesium ribbon


Place it in the water Test the productmixture with blue and red litmus papers


Repeat with Calcium metal


Observations


Surface of magnesium covered by bubbles of colourless gas


Colourless solution formed


Effervescencebubblesfizzing takes place in Calcium


Red litmus paper turns blue


Blue litmus paper remains blue


Explanations


Magnesium slowly reacts with cold water to form Magnesium hydroxide and bubbles of Hydrogen gas that stick on the surface of the ribbon


Mgs  2H2O l  MgOH2aq  H2 g


Calcium moderately reacts with cold water to form Calcium hydroxide and produce a steady stream of Hydrogen gas


Cas  2H2O l  Ca OH2aq  H2 g


Reaction with water vapoursteam


Experiment


Put some cotton wool soaked in waterwet sand in a long boiling tube


Coil a well polished magnesium ribbon into the boiling tube


Ensure the coil touches the side of the boiling tube Heat the cotton woolsand slightly then strongly heat the Magnesium ribbon


Set up of apparatus


Observations


Magnesium glows red hot then burns with a blindening flame


Magnesium continues to glowburning even without more heating


White solidresidue


colourless gas collected over water


Explanation


On heating wet sand steam is generated which drives out the air that would otherwise react with oxidize the ribbon


Magnesium burns in steamwater vapour generating enough heat that ensures the reaction goes to completion even without further heating White Magnesium oxide is formed and hydrogen gas is evolved


To prevent suck back the delivery tube should be removed from the water before heating is stopped at the end of the experiment


Mgs  H2O l  MgOs  H2 g


Reaction with chlorine gas


Lower slowly burning magnesium ribbonshavings into a gas jar containing Chlorine gas Repeat with a hot piece of calcium metal


Observation


Magnesium continues to burn in chlorine with a bright blindening flame


Calcium continues to burn for a short time


White solid formed


Pale green colour of chlorine fades


Magnesium continues to burn in chlorine gas forming white magnesium oxide solid


Mgs  Cl2 g  MgCl2 s


Calcium burns slightly in chlorine gas to form white calcium oxide solid Calcium oxide formed coat unreacted Calcium stopping further reaction


Cas  Cl2 g  CaCl2 s


Reaction with dilute acids


Experiment


Place about 40cm3 of 01M dilute sulphuric VI acid into a test tube Add about 10cm length of magnesium ribbon into the test tube Cover the mouth of the test tube using a thumb Release the gas and test the gas using a burning splint


Repeat with about 40cm3 of 01M dilute hydrochloricnitric V acid


Repeat with 01g of Calcium in a beaker with all the above acid


Caution Keep distance when using calcium


Effervescencefizzingbubbles with dilute sulphuric VI and nitric V acids


Little Effervescencefizzingbubbles with calcium and dilute sulphuric VI acid


Colourless gas produced that extinguishes a burning splint with an explosion pop sound


No gas is produced with Nitric V acid


Colourless solution is formed


Explanation


Dilute acids react with alkaline earth metals to form a salt and produce hydrogen gas


Nitric V acid is a strong oxidizing agent It quickly oxidizes the hydrogen produced to water


Calcium is very reactive with dilute acids and thus a very small piece of very dilute acid should be used


Chemical equations


Mgs  H2SO4 aq  MgSO4 aq  H2 g


Mgs  2HNO3 aq  MgNO32aq  H2 g


Mgs  2HCl aq  MgCl2aq  H2 g


Cas  H2SO4 aq  CaSO4s  H2 g


insoluble CaSO4s coatcover Cas


Cas  2HNO3 aq  CaNO32aq  H2 g


Cas  2HCl aq  CaCl2aq  H2 g


Bas  H2SO4 aq  BaSO4s  H2 g


insoluble BaSO4s coatcover Bas


Bas  2HNO3 aq  BaNO32aq  H2 g


Bas  2HCl aq  BaCl2aq  H2 g


The table below shows some compounds of some alkaline earth metals


Some uses of alkaline earth metals include


iMagnesium hydroxide is a nontoxicpoisonous mild base used as an anti acid medicine to relieve stomach acidity


ii Making duralumin Duralumin is an alloy of Magnesium and aluminium used for making aeroplane bodies because it is light


iii Making plaster of ParisCalcium sulphate VI is used in hospitals to set a fractures bone


iiiMaking cementCalcium carbonate is mixed with clay and sand then heated to form cement for constructionbuilding


ivRaise soil pHQuicklimecalcium oxide is added to acidic soils to neutralize and raise the soil pH in agricultural farms


v As nitrogenous fertilizerCalcium nitrate V is used as an agricultural fertilizer because plants require calcium for proper growth


viIn the blast furnaceLimestone is added to the blast furnace to produce more reducing agent and remove slag in the blast furnace for extraction of Iron


cGroup VII elements Halogens


Group VII elements are called Halogens They are all non metals They include


All halogen atoms have seven electrons in the outer energy level They acquiregain one electron in the outer energy level to be stable They therefore are therefore monovalent They exist in oxidation state X


The number of energy levels increases down the group from Fluorine to Astatine The more the number of energy levels the biggerlarger the atomic size eg


The atomic sizeradius of Chlorine is biggerlarger than that of Fluorine because Chlorine has more3 energy levels than Fluorine 2 energy levels


Atomic radius and ionic radius of Halogens increase down the group as the number of energy levels increases


The atomic radius of Halogens is smaller than the ionic radius This is because they react by gainingacquiring extra one electron in the outer energy level The effective nuclear attraction on the moreextra electrons decreases The incoming extra electron is also repelled causing the outer energy level to expand to reduce the repulsion and accommodate more electrons


Table showing the atomic and ionic radius of four Halogens


The atomic radius of Chlorine is 0099nM The ionic radius of Cl is 0181nM This is because Chlorine atommolecule reacts by gainingacquiring extra one electron The moreextra electronsenergy level experience less effective nuclear attraction pull towards the nucleus The outer energy level expandincrease to reduce the repulsion of the existing and incoming gained acquired electrons


Electronegativity


The ease of gainingacquiring extra electrons is called electronegativity All halogens are electronegative Electronegativity decreases as atomic radius increase This is because the effective nuclear attraction on outer electrons decreases with increase in atomic radius


The outer electrons experience less nuclear attraction and thus ease of gainingacquiring extra electrons decrease


It is measured using Paulings scale


Where Fluorine with Pauling scale 40 is the most electronegative element and thus the highest tendency to acquiregain extra electron


Table showing the electronegativity of the halogens


The electronegativity of the halogens decrease down the group from fluorine to Astatine This is because atomic radius increases down the group and thus decrease electron  attracting power down the group from fluorine to astatine


Fluorine is the most electronegative element in the periodic table because it has the small atomic radius


Electron affinity


The minimum amount of energy required to gainacquire an extra electron by an atom of element in its gaseous state is called 1st electron affinity The SI unit of electron affinity is kilojoules per molekJmole1 Electron affinity depends on atomic radius The higher the atomic radius the less effective the nuclear attraction on outer energy level electrons and thus the lower the electron affinity For halogens the 1st electron affinity decrease down the group as the atomic radius increase and the effective nuclear attraction on outer energy level electrons decrease Due to its small sizeatomic radius Fluorine shows exceptionally low electron affinity This is because a lot of energy is required to overcome the high repulsion of the existing and incoming electrons


Table showing the election affinity of halogens for the process


X  e  X


The higher the electron affinity the more stable theionie


Cl is a more stable ion than Br because it has a more negative  exothermic electron affinity than Br


Electron affinity is different from


i Ionization energy


Ionization energy is the energy required to losedonate an electron in an atom of an element in its gaseous state while electron affinity is the energy required to gainacquire extra electron by an atom of an element in its gaseous state


ii Electronegativity


Electron affinity is the energy required to gain an electron in an atom of an element in gaseous state It involves the process


Xg  e  Xg


Electronegativity is the easetendency of gaining acquiring electrons by an element during chemical reactions


It does not involve use of energy but theoretical arbitrary Pauling scale of measurements


Physical properties


State at room temperature


Fluorine and Chlorine are gases Bromine is a liquid and Iodine is a solid Astatine is radioactive


All halogens exist as diatomic molecules bonded by strong covalent bond Each molecule is joined to the other by weak intermolecular forces Vanderwaals forces


MeltingBoiling point


The strength of intermolecularVanderwaals forces of attraction increase with increase in molecular sizeatomic radius


Iodine has therefore the largest atomic radius and thus strongest intermolecular forces to make it a solid


Iodine sublimes when heated to form caution highly toxicpoisonous purple vapour


This is because Iodine molecules are held together by weak vanderwaalsintermolecular forces which require little heat energy to break


Electrical conductivity


All Halogens are poor conductors of electricity because they have no free delocalized electrons


Solubility in polar and nonpolar solvents


All halogens are soluble in water polar solvent


When a boiling tube containing either chlorine gas or bromine vapour is separately inverted in a beaker containing distilled water and tetrachloromethane nonpolar solvent the level of solution in boiling tube rises in both water and tetrachloromethane


This is because halogen are soluble in both polar and nonpolar solvents Solubility of halogens in waterpolar solvents decrease down the group Solubility of halogens in nonpolar solvent increases down the group


The level of water in chlorine is higher than in bromine and the level of tetrachloromethane in chlorine is lower than in bromine


Caution Tetrachloromethane  Bromine vapour and Chlorine gas are all highly toxicpoisonous


Table showing the physical properties of Halogens


Chemical properties


iDisplacement


Experiment


Place separately in test tubes about 5cm3 of sodium chloride Sodium bromide and Sodium iodide solutions


Add 5 drops of chlorine water to each test tube


Repeat with 5 drops of bromine water instead of chlorine water


Observation


Using Chlorine water


Yellow colour of chlorine water fades in all test tubes except with sodium chloride


Coloured Solution formed


Using Bromine water


Yellow colour of bromine water fades in test tubes containing sodium iodide


Explanation


The halogens displace each other from their solution The more electronegative displace the less electronegative from their solution


Chlorine is more electronegative than bromine and iodine


On adding chlorine water bromine and Iodine are displaced from their solutions by chlorine


Bromine is more electronegative than iodide but less 6than chlorine


On adding Bromine water iodine is displaced from its solution but not chlorine


Table showing the displacement of the halogens


V means there is displacement x  means there is no displacement


Chemical ionic equations


With Fluorine


F2g  2NaClaq  2NaFaq  Cl2aq


F2g  2Claq  2Faq  Cl2aq


F2g  2NaBraq  2NaFaq  Br2aq


F2g  2Braq  2Faq  Br2aq


F2g  2NaIaq  2NaFaq  I2aq


F2g  2Iaq  2Faq  I2aq


With chlorine


Cl2g  2NaClaq  2NaClaq  Br2aq


Cl2g  2Braq  2Claq  Br2aq


Cl2g  2NaIaq  2NaClaq  I2aq


Cl2g  2Iaq  2Claq  I2aq


With Bromine


Br2g  2NaIaq  2NaBraq  I2aq


Br2g  2Iaq  2Braq  I2aq


Uses of halogens


Florine  manufacture of PTFE Poly tetra fluoroethene synthetic fiber


Reduce tooth decay when added in small amountsquantities in tooth paste


NB large small quantities of fluorine fluoride ions in water cause browning of teethflourosis


Hydrogen fluoride is used to engrave words pictures in glass


Bromine  Silver bromide is used to make light sensitive photographic paperfilms


Iodide  Iodine dissolved in alcohol is used as medicine to kill bacteria in skin cuts It is called tincture of iodine


The table below to show some compounds of halogens


Below is the table showing the bond energy of four halogens


Bond Bond energy k J mole1


ClCl 242


BrBr 193


II 151


What do you understand by the term bond energy


Bond energy is the energy required to break form one mole of chemical bond


Explain the trend in bond Energy of the halogens above


Decrease down the group from chlorine to Iodine


Atomic radius increase down the group decreasing the energy required to break the covalent bonds between the larger atom with reduced effective nuclear  charge an outer energy level that take part in bonding


cGroup VIII elements Noble gases


Group VIII elements are called Noble gases They are all non metals Noble gases occupy about 10 of the atmosphere as colourless gaseous mixture Argon is the most abundant with 09


They exist as monatomic molecules with very weak vanderwaals intermolecular forces holding the molecules


They include


All noble gas atoms have a stable duplettwo electrons in the 1st energy level or octeteight electrons in other outer energy levelin the outer energy level They therefore do not acquiregain extra electron in the outer energy level or donatelose They therefore are therefore zerovalent


The number of energy levels increases down the group from Helium to Randon The more the number of energy levels the biggerlarger the atomic sizeradius eg


The atomic sizeradius of Argon is biggerlarger than that of Neon because Argon has more3 energy levels than Neon 2 energy levels


Atomic radius noble gases increase down the group as the number of energy levels increases


The effective nuclear attraction on the outer electrons thus decrease down the group


The noble gases are generally unreactive because the outer energy level has the stable octetduplet The stable octetduplet in noble gas atoms lead to comparatively very high 1st ionization energy This is because losing donating an electron from the stable atom require a lot of energy to losedonate and make it unstable


As atomic radius increase down the group and the 1st ionization energy decrease very electronegative elements like Oxygen and Fluorine are able to react and bond with lower members of the noble gaseseg


Xenon reacts with Fluorine to form a covalent compound XeF6This is because the outer electronsenergy level if Xenon is far from the nucleus and thus experience less effective nuclear attraction


Noble gases have low melting and boiling points This is because they exist as monatomic molecules joined by very weak intermolecularvanderwaals forces that require very little energy to weaken and form liquid and break to form a gas


The intermolecularvanderwaals forces increase down the group as the atomic radiussize increase from Helium to Radon The melting and boiling points thus increase also down the group


Noble gases are insoluble in water and are poor conductors of electricity


Uses of noble gases


Argon is used in light bulbs to provide an inert environment to prevent oxidation of the bulb filament


Argon is used in arch welding as an insulator


Neon is used in street and advertisement light


Helium is mixed with Oxygen during deep sea diving and mountaineering


Helium is used in weather balloon for meteorological research instead of Hydrogen because it is unreactiveinertHydrogen when impure can ignite with an explosion


Helium is used in making thermometers for measuring very low temperatures


CHEMISTRY OF CARBON A CARBON


Carbon is an element in Group IVGroup 4of the Periodic table It has atomic number 6 and electronic configuration 24 and thus has four valence electronstetravalentIt does not easily ionize but forms strong covalent bonds with other elements including itself


aOccurrence


Carbon mainly naturally occurs as


iallotropes of carbon ie graphite diamond and fullerenes


iiamorphous carbon in coal peat charcoal and coke


iiicarbonIVoxide gas accounting 003 by volume of normal air in the atmosphere


bAllotropes of Carbon


Carbon naturally occur in two main crystalline allotropic forms carbongraphite and carbondiamond


c Properties of Carbon


iPhysical properties of carbon


Carbon occur widely and naturally as a black solid


It is insoluble in water but soluble in carbon disulphide and organic solvents


It is a poor electrical and thermal conductor


iiChemical properties of carbon


I Burning


Experiment


Introduce a small piece of charcoal on a Bunsen flame then lower it into a gas jar containing Oxygen gas Put three drops of water Swirl Test the solution with blue and red litmus papers


Observation


Carbon chars then burns with a blue flame


Colourless and odourless gas produced


Solution formed turn blue litmus paper faint red Red litmus paper remains red


Explanation


Carbon burns in air and faster in Oxygen with a blue nonsootynonsmoky flame forming Carbon IV oxide gas Carbon burns in limited supply of air with a blue nonsootynonsmoky flame forming Carbon IV oxide gas Carbon IV oxide gas dissolve in water to form weak acidic solution of Carbonic IVacid


Chemical Equation


Cs  O2g  CO2g in excess air


2Cs  O2g  2COg in limited air


CO2g  H2O l  H2CO3 aq very weak acid


II Reducing agent


Mix thoroughly equal amounts of powdered charcoal and copper IIoxide into a crucible Heat strongly


Colour change from black to brown


Carbon is a reducing agent For ages it has been used to reducing metal oxide ores to metal itself oxidized to carbon IV oxide gas Carbon reduces black copper II oxide to brown copper metal


2CuOs  Cs  2Cus  CO2g


black brown


2PbOs  Cs  2Pbs  CO2g


brown when hot grey


yellow when cool


2ZnOs  Cs  2Zns  CO2g


yellow when hot grey


white when cool


Fe2O3s  3Cs  2Fes  3CO2g


brown when hotcool grey


Fe3O4 s  4Cs  3Fes  4CO2g


B COMPOUNDS OF CARBON


The following are the main compounds of Carbon


iiCarbonIIOxideCO


iiiCarbonateIV CO32and hydrogen carbonateIVHCO3


ivSodium carbonateNa2CO3


i CarbonIVOxide CO2


aOccurrence


CarbonIVoxide is found


in the air atmosphere as 003 by volume


a solid carbonIVoxide mineral in Esageri near Eldame Ravine and Kerita near Limuru in Kenya


bSchool Laboratory preparation


In the school laboratory carbonIVoxide can be prepared in the school laboratory from the reaction of marble chipsCaCO3or sodium hydrogen carbonateNaHCO3 with dilute hydrochloric acid


cProperties of carbonIVoxide gasQuestions


1Write the equation for the reaction for the school laboratory preparation of carbon IVoxide gas


Any carbonate reacted with dilute hydrochloric acid should be able to generate carbon IVoxide gas


Chemical equations


CaCO3s  2HClaq  CaCO3 aq  H2Ol  CO2 g


ZnCO3s  2HClaq  ZnCO3 aq  H2Ol  CO2 g


MgCO3s  2HClaq  MgCO3 aq  H2Ol  CO2 g


CuCO3s  2HClaq  CuCO3 aq  H2Ol  CO2 g


NaHCO3s  HClaq  Na2CO3 aq  H2Ol  CO2 g


KHCO3s  HClaq  K2CO3 aq  H2Ol  CO2 g


2What method of gas collection is used in preparation of CarbonIVoxide gas Explain


Downward delivery upward displacement of airover mercury


CarbonIVoxide gas is about 1 times denser than air


3What is the purpose of


awater


To absorb the more volatile hydrogen chloride fumes produced during the vigorous reaction


bsodium hydrogen carbonate


To absorb the more volatile hydrogen chloride fumes produced during the vigorous reaction and by reacting with the acid to produce more carbon IVoxide gas


Chemical equation


cconcentrated sulphuricVIacid


To dry the gasas a drying agent


4Describe the smell of carbonIVoxide gas


Colourless and odourless


5 Effect on lime water


Experiment


Bubbled carbonIVoxide gas into a test tube containing lime water for about three minutes


Observation


White precipitate is formed


White precipitate dissolved when excess carbonIVoxide gas is bubbled


Explanation


CarbonIVoxide gas reacts with lime waterCaOH2 to form an insoluble white precipitate of calcium carbonate Calcium carbonate reacts with more CarbonIV oxide gas to form soluble Calcium hydrogen carbonate


CaOH2aq  CO2 g  CaCO3 s  H2Ol


CaCO3 aq  H2Ol  CO2 g  CaHCO3 2 aq


6 Effects on burning Magnesium ribbon


Lower a piece of burning magnesium ribbon into a gas jar containing carbon IVoxide gas


The ribbon continues to burn with difficulty


White ashsolid is formed


Black specksolidparticles formed on the side of gas jar


Carbon IV oxide gas does not support combustionburningMagnesium burn to producerelease enough heat energy to decompose Carbon IV oxide gas to carbon and oxygenMagnesium continues to burn in Oxygen forming white Magnesium Oxide solidashBlack speckparticle of carboncharcoal residue forms on the sides of reaction flask During the reaction Carbon IV oxide is reduced Oxidizing agentto carbon while Magnesium is Oxidized to Magnesium Oxide


Chemical equation


2Mgs  CO2 g  C s  2MgOl


7 Dry and wet litmus papers were separately put in a gas jar containing dry carbon IV oxide gas State and explain the observations made


Blue dry litmus paper remain blue


Red dry litmus paper remain Red


Blue wetdampmoist litmus paper turns red


Red wetdampmoist litmus paper remain red


Explanation


Dry Carbon IV oxide gas is a molecular compound that does not dissociateionize to release H and thus has no effect on litmus papers


Wetdampmoist litmus paper contains water that dissolvesreact with dry carbon IV oxide gas to form the weak solution of carbonic IV acid H2CO3


Carbonic IV acid dissociateionizes to a few little free H and CO32


The few H aq ions are responsible for turning blue litmus paper to faint red showing the gas is very weakly acidic


H2CO3aq  2H aq  CO32aq


8 Explain why Carbon IV oxide cannot be prepared from the reaction of


i Marble chips with dilute sulphuric VI acid


Reaction forms insoluble calcium sulphate VI that covercoat unreacted marble chips stopping further reaction


CaCO3s  H2SO4 aq  CaSO4 s  H2Ol  CO2 g


PbCO3s  H2SO4 aq  PbSO4 s  H2Ol  CO2 g


BaCO3s  H2SO4 aq  BaSO4 s  H2Ol  CO2 g


ii Lead II carbonate with dilute Hydrochloric acid


Reaction forms insoluble Lead IIChloride that covercoat unreacted LeadII carbonate stopping further reaction unless the reaction mixture is heated Lead II Chloride is soluble in hot water


Chemical equation


PbCO3s  2HCl aq  PbCl2 s  H2Ol  CO2 g


9 Describe the test for the presence of Carbon IV oxide


Using burning splint


Lower a burning splint into a gas jar suspected to contain Carbon IV oxide gas The burning splint is extinguished


Using Lime water


Bubble the gas suspected to be Carbon IV oxide gas A white precipitate that dissolves in excess bubbling is formed


CaOH2aq  CO2 g  CaCO3 s  H2Ol


CaCO3 aq  H2Ol  CO2 g  CaHCO3 2 aq


10State three main uses of Carbon IVoxide gas


iIn the Solvay process for the manufacture of soda ashsodium carbonate


iiIn preservation of aerated drinks


iiiAs fire extinguisher because it does not support combustion and is denser than air


ivIn manufacture of Baking powder


ii Carbon II Oxide CO


aOccurrence


Carbon II oxide is found is found from incomplete combustion of fuels like petrol charcoal liquefied Petroleum GasLPG


bSchool Laboratory preparation


In the school laboratory carbonIIoxide can be prepared from dehydration of methanoic acidFormic acidHCOOH or Ethan12dioic acidOxalic acidHOOCCOOH using concentrated sulphuricVI acid Heating is necessary


cProperties of Carbon II OxideQuestions


1 Write the equation for the reaction for the preparation of carbonIIoxide using


iMethod 1


Chemical equation


HOOCCOOHs ConcH2SO4 COg  CO2 g  H2Ol


H2C2O4s ConcH2SO4 COg  CO2 g  H2Ol


iiMethod 2


HCOOHs ConcH2SO4 COg  H2Ol


H2CO2s ConcH2SO4 COg  H2Ol


2 What method of gas collection is used during the preparation of carbon II oxide


Over water because the gas is insoluble in water


Downward delivery because the gas is 1  times denser than air


3 What is the purpose of


i Potassium hydroxidesodium hydroxide in Method 1


To absorb remove carbon II oxide produced during the reaction


2KOH aq  CO2 g  K2CO3 s  H2Ol


2NaOH aq  CO2 g  Na2CO3 s  H2Ol


ii Concentrated sulphuricVIacid in Method 1 and 2


Dehydrating agent removes the element of water Hydrogen and Oxygen in ratio 21 present in both methanoic and ethan12dioic acid


4 Describe the smell of carbon II oxide


Colourless and odourless


5 State and explain the observation made when carbonIVoxide is bubbled in lime water for a long time


No white precipitate is formed


6 Dry and wetmoistdamp litmus papers were separately put in a gas jar containing dry carbon IV oxide gas State and explain the observations made


Observation


blue dry litmus paper remains blue


red dry litmus paper remains red


wetmoistdamp blue litmus paper remains blue


wetmoistdamp red litmus paper remains red


Explanation


CarbonIIoxide gas is a molecular compound that does not dissociate ionize to release H ions and thus has no effect on litmus papers CarbonIIoxide gas is therefore a neutral gas


7 Carbon II oxide gas was ignited at the end of a generator as below


iState the observations made in flame K


Gas burns with a blue flame


iiWrite the equation for the reaction taking place at flame K


2COg  O2 g  2CO2 g


8 Carbon II oxide is a reducing agent Explain


Experiment


Pass carbon II oxide through glass tube containing copper II oxide Ignite any excess poisonous carbon II oxide


Colour change from black to brown Excess carbon II oxide burn with a blue flame


Carbon is a reducing agent It is used to reduce metal oxide ores to metal itself oxidized to carbon IV oxide gas Carbon II Oxide reduces black copper II oxide to brown copper metal


Chemical Equation


CuOs  COg  Cus  CO2g


black brown


PbOs  COg  Pbs  CO2g


brown when hot grey


yellow when cool


ZnOs  COg  Zns  CO2g


yellow when hot grey


white when cool


Fe2O3s  3COs  2Fes  3CO2g


brown when hotcool grey


Fe3O4 s  4COg  3Fes  4CO2g


These reactions are used during the extraction of many metals from their ore


9 Carbon II oxide is a pollutant Explain


Carbon II oxide is highly poisonoustoxicIt preferentially combine with haemoglobin to form stable carboxyhaemoglobin in the blood instead of oxyhaemoglobinThis reduces the free haemoglobin in the blood causing nausea  coma then death


10 The diagram below show a burning charcoal stoveburnerjiko Use it to answer the questions that follow


Explain the changes that take place in the burner


Explanation


Charcoal stove has air holes through which air enters Air oxidizes carbon to carbon IV oxide gas at region I This reaction is exothermic H producing more heat


Chemical equation


Cs  O2g  CO2g


Carbon IV oxide gas formed rises up to meet more charcoal which reduces it to Carbon II oxide gas


2CO2 g  O2g  2CO g


At the top of burner in region II Carbon IIoxide gas is further oxidized to CarbonIVoxide gas if there is plenty of air but escape if the air is limited poisoning the living things around


2CO g  O2g  2CO2 g


excess air


11 Describe the test for the presence of carbonIIoxide gas


Experiment


BurnIgnite the pure sample of the gas PassBubble the products into lime waterCalcium hydroxide


Observation


Colourless gas burns with a blue flame A white precipitate is formed that dissolve on further bubbling of the products


2CO g  O2g  2CO2 g gas burns with blue flame


CaOH 2 aq  CO2 g  CaCO3 s  H2Ol


CO2 g  CaCO3 s  H2Ol  CaHCO3 2 aq


12 State the main uses of carbon IIoxide gas


i As a fuel water gas


iiAs a reducing agent in the blast furnace for extracting iron from iron oreMagnetiteHaematite


iiiAs a reducing agent in extraction of Zinc from Zinc oreZinc blende


iv As a reducing agent in extraction of Lead from Lead oreGalena


v As a reducing agent in extraction of Copper from Copper iron sulphideCopper pyrites


iiiCarbonateIV CO32and hydrogen carbonateIVHCO3


1Carbonate IV CO32 are normal salts derived from carbonicIVacid H2CO3 and hydrogen carbonate IV HCO3 are acid salts derived from carbonicIVacid


CarbonicIVacidH2CO3 is formed when carbonIVoxide gas is bubbled in water It is a dibasic acid with two ionizable hydrogens


H2CO3aq 2Haq  CO32aq


H2CO3aq  Haq  HCO3  aq


2Carbonate IV CO32 are insoluble in water except Na2CO3  K2CO3 and NH42CO3


3Hydrogen carbonate IV HCO3 are soluble in water Only five hydrogen carbonates exist Na HCO3  KHCO3 NH4HCO3 CaHCO32 and MgHCO32


CaHCO32 and MgHCO32 exist only in aqueous solutions


3The following experiments show the effect of heat on Carbonate IV CO32 and Hydrogen carbonate IV HCO3 salts


Experiment


In a clean dry test tube place separately about 10 of the following


ZincIIcarbonateIV sodium hydrogen carbonateIV sodium carbonateIV Potassium carbonateIV ammonium carbonateIV potassium hydrogen carbonateIV LeadIIcarbonateIV IronIIcarbonateIV and copperIIcarbonateIV Heat each portion gently the strongly Test any gases produced with lime water


Observation


iColorless droplets form on the cooler parts of test tube in case of sodium carbonateIV and Potassium carbonateIV


iiWhite residuesolid left in case of sodium hydrogen carbonateIV sodium carbonateIV Potassium carbonateIV and potassium hydrogen carbonateIV


iiiColour changes from bluegreen to black in case of copperIIcarbonateIV


iv Colour changes from green to brownyellow in case of Iron IIcarbonateIV


v Colour changes from white when cool to yellow when hot in case of Zinc II carbonateIV


vi Colour changes from yellow when cool to brown when hot in case of Lead II carbonateIV


viiColourless gas produced that forms a white precipitate with lime water in all cases


Explanation


1 Sodium carbonateIV and Potassium carbonateIV exist as hydrated salts with 10 molecules of water of crystallization that condenses and collects on cooler parts of test tube as a colourless liquid


Chemical equation


Na2CO3 10H2Os  Na2CO3 s  10H2Ol


K2CO3 10H2Os  K2CO3 s  10H2Ol


2 Carbonate IV CO32 and Hydrogen carbonate IV HCO3 salts decompose on heating except Sodium carbonateIV and Potassium carbonateIV


a Sodium hydrogen carbonateIV and Potassium hydrogen carbonateIV decompose on heating to form sodium carbonateIV and Potassium carbonateIVWater and carbonIVoxide gas are also produced


2NaHCO3 s  Na2CO3 s  H2Ol  CO2 g


white white


2KHCO3 s  K2CO3 s  H2Ol  CO2 g


b Calcium hydrogen carbonateIV and Magnesium hydrogen carbonateIV decompose on heating to form insoluble Calcium carbonateIV and Magnesium carbonateIVWater and carbonIVoxide gas are also produced


CaHCO32 aq  CaCO3 s  H2Ol  CO2 g


Colourless solution white


MgHCO32 aq  MgCO3 s  H2Ol  CO2 g


c Ammonium hydrogen carbonateIV decompose on heating to form ammonium carbonateIV Water and carbonIVoxide gas are also produced


2NH4HCO3 s  NH42CO3 s  H2Ol  CO2 g


dAll other carbonates decompose on heating to form the metal oxide and produce carbonIVoxide gas eg


MgCO3 s  MgO s  CO2 g


white solid white solid


Chemical equation


BaCO3 s  BaO s  CO2 g


CaCO3 s  CaO s  CO2 g


CuCO3 s  CuO s  CO2 g


bluegreen solid black solid


ZnCO3 s  ZnO s  CO2 g


white solid white solid when cool


Yellow solid when hot


PbCO3 s  PbO s  CO2 g


white solid yellow solid when cool


brown solid when hot


4The following experiments show the presence of Carbonate IV CO32 and Hydrogen carbonate IV HCO3 ions in sample of a salt


aUsing LeadII nitrateV


I Using a portion of salt solution in a test tube add four drops of LeadIInitrateVsolutionPreserve


II To the preserved solution add six drops of dilutte nitricVacid Preserve


II To the preserved sample that forms a precipitate heat to boil


II To the preserved sample that do not form a precipitate add three drops of acidified potassium manganateVIIlime water


ExperimentsObservations


bUsing BariumIInitrateV BariumIIchloride


I To about 5cm3 of a salt solution in a test tube add four drops of BariumII nitrate V  BariumIIchloride Preserve


II To the preserved sample in I above add six drops of 2M nitricV acid  Preserve


Observation 1


Observation 2


IIITo the preserved sample observation 2 in II above add 4 drops of acidified potassium manganateVII dichromateVI


Explanations


Using LeadIInitrateV


iLeadIInitrateV solution reacts with chloridesCl Sulphate VI salts SO42  Sulphate IVsalts SO32 and carbonatesCO32 to form the insoluble white precipitate of LeadIIchloride LeadIIsulphateVI LeadII sulphate IV and LeadIIcarbonateIV


Chemicalionic equation


Pb2aq  Cl aq  PbCl2s


Pb2aq  SO42 aq  PbSO4 s


Pb2aq  SO32 aq  PbSO3 s


Pb2aq  CO32 aq  PbCO3 s


iiWhen the insoluble precipitates are acidified with nitricV acid


LeadIIchloride and LeadIIsulphateVI do not react with the acid and thus their white precipitates remain persists


LeadII sulphate IV and LeadIIcarbonateIV reacts with the acid to form soluble LeadII nitrate V and produceeffervescesfizzesbubbles out sulphurIVoxide and carbonIVoxide gases respectively


PbSO3 s  2Haq  H2 O l  Pb2aq  SO2 g


PbCO3 s  2Haq  H2 O l  Pb2aq  CO2 g


iiiWhen LeadIIchloride and LeadIIsulphateVI are heatedwarmed


LeadIIchloride dissolves in hot wateron boilingrecrystallizes on cooling


LeadIIsulphateVI do not dissolve in hot water thus its white precipitate persistsremains on heatingboiling


ivWhen sulphurIVoxide and carbonIVoxide gases are produced


sulphurIVoxide will decolorize acidified potassium manganateVII and  or Orange colour of acidified potassium dichromateVI will turns to green CarbonIVoxide will not


Chemical equation


5SO32aq  2MnO4 aq 6Haq  5SO42aq  2Mn2aq  3H2Ol


purple colourless


3SO32aq  Cr2O72aq 8Haq  3SO42aq  2Cr3aq  4H2Ol


Orange green


CarbonIVoxide forms an insoluble white precipitate of calcium carbonate if three drops of lime water are added into the reaction test tube when effervescence is taking place SulphurIVoxide will not


CaOH2aq  CO2 g  CaCO3s  H2Ol


These tests should be done immediately after acidifying to ensure the gases produced react with the oxidizing agentslime water


Using BariumIInitrateV BariumIIChloride


iBariumIInitrateV and or BariumIIchloride solution reacts with Sulphate VI salts SO42  Sulphate IVsalts SO32 and carbonatesCO32 to form the insoluble white precipitate of BariumIIsulphateVI BariumII sulphate IV and BariumIIcarbonateIV


Chemicalionic equation


Ba2aq  SO42 aq  BaSO4 s


Ba2aq  SO32 aq  BaSO3 s


Ba2aq  CO32 aq  BaCO3 s


Barium IIsulphateVI do not react with the acid and thus its white precipitates remain persists


BariumII sulphate IV and BariumIIcarbonateIV reacts with the acid to form soluble BariumII nitrate V and produce effervesces fizzes bubbles out sulphurIVoxide and carbonIVoxide gases respectively


BaSO3 s  2Haq  H2 O l  Ba2aq  SO2 g


BaCO3 s  2Haq  H2 O l  Ba2aq  CO2 g


iii When sulphurIVoxide and carbonIVoxide gases are produced


Chemical equation


purple colourless


Orange green


iii Sodium carbonateIV Na2CO3


aExtraction of sodium carbonate from soda ash


Sodium carbonate naturally occurs in Lake Magadi in Kenya as Tronatrona is the double salt  sodium sesquicarbonate NaHCO3 Na2CO3 H2OIt is formed from the volcanic activity that takes place in Lake Naivasha Nakuru Bogoria and Elementeita All these lakes drain into Lake Magadi through underground rivers Lake Magadi has no outlet


Solubility of Trona decrease with increase in temperatureHigh temperature during the day causes trona to naturally crystallize It is mechanically scoopeddredgeddug and put in a furnace


Inside the furnace trona decompose into soda ashsodium carbonate


2NaHCO3 Na2CO3 H2O s  3Na2CO3 s  5H2Ol  CO2 g


trona soda ash


Soda ash is then bagged and sold as Magadi sodaIt is mainly used


iin making glass to lower the melting point of raw materials sandSiO2 from 1650oC and CaO from 2500oC to around 1500oC


iiin softening hard water


iiiin the manufacture of soapless detergents


ivSwimming pool pH increaser


Sodium chloride is also found dissolved in the lake Solubility of sodium chloride decrease with decreases in temperature sodium chloride has lower solubility at lower temperatures When temperatures decrease at night it crystallize out The crystals are then mechanically dugdredged scooped then packed for sale as animalcattle feeds and seasoning food


Summary flow diagram showing the extraction of Soda ash from Trona


bThe Solvay process for industrial manufacture of sodium carbonateIV


iRaw materials


Brine Concentrated Sodium chloride from salty seaslakes


Ammonia gas from Haber


Limestone Calcium carbonate from chalk limestone rich rocks


Water from riverslakes


iiChemical processes


Ammonia gas is passed up to meet a downward flow of sodium chloride solution  brine to form ammoniated brineammoniacal brine mixture in the ammoniated brine chamber


The ammoniated brine mixture is then pumped up atop the carbonator solvay tower


In the carbonator solvay tower ammoniated brineammoniacal brine mixture slowly trickle down to meet an upward flow of carbonIVoxide gas


The carbonator is shelved packed with quartzbroken glass to


i reduce the rate of flow of ammoniated brineammoniacal brine mixture


iiincrease surface area of the liquid mixture to ensure a lot of ammoniated brineammoniacal brine mixture react with carbonIVoxide gas


Insoluble sodium hydrogen carbonate and soluble ammonium chloride are formed from the reaction


Chemical equation


CO2g  H2Ol  NaCl aq  NH3g  NaHCO3s  NH4Claq


The products are then filtered Insoluble sodium hydrogen carbonate forms the residue while soluble ammonium chloride forms the filtrate


Sodium hydrogen carbonate itself can be used


i as baking powder and preservation of some soft drinks


ii as a buffer agent and antacid in animal feeds to improve fibre digestion


iii making dry chemical fire extinguishers


In the Solvay process Sodium hydrogen carbonate is then heated to form Sodium carbonatesoda ash water and carbon IV oxide gas


2NaHCO3 s  Na2CO3s  CO2g  H2Ol


Sodium carbonate is stored ready for use in


i during making glasslowering the melting point of mixture of sandSiO2 from 1650oC and CaO from 2500oC to around 1500oC


ii in softening hard water


iii in the manufacture of soapless detergents


iv swimming pool pH increaser


Water and carbonIVoxide gas are recycled back to the ammoniated brineammoniacal brine chamber


More carbonIVoxide is produced in the kilnfurnace Limestone is heated to decompose into Calcium oxide and carbonIVoxide


CaCO3 s  CaOs  CO2g


CarbonIVoxide is recycled to the carbonatorsolvay tower Carbon IVoxide is added water in the slaker to form Calcium hydroxide This process is called slaking


Chemical equation


CaOs  H2O l  CaOH2 aq


Calcium hydroxide is mixed with ammonium chloride from the carbonatorsolvay tower in the ammonia regeneration chamber to form Calcium chloride water and more ammonia gas


CaOH2 aq 2NH4Cl aq  CaCl2s  2NH3g  H2Ol


NH3g and H2Ol are recycled


Calcium chloride may be used


ias drying agent in the school laboratory during gas preparation except ammonia gas


iito lower the melting point of solid sodium chloride  rock salt salts during the Downs process for industrial extraction of sodium metal


Detailed Summary flow diagram of Solvay Process


Practice


1 The diagram below shows part of the Solvay process used in manufacturing sodium carbonate Use it to answer the questions that follow


aExplain how Sodium Chloride required for this process is obtained from the sea


Sea water is pumped scooped into shallow pods Evaporation of most of the water takes place leaving a very concentrated solution


bi Name process


I Filtration


II Decomposition


ii Write the equation for the reaction in process


Process I


Chemical equation


CO2g  H2Ol  NaCl aq  NH3g  NaHCO3s  NH4Claq


Process II


2NaHCO3 s  Na2CO3s  CO2g  H2Ol


ci Name two substances recycled in the solvay process


Ammonia gas  CarbonIVOxide and Water


iiWhich is the byproduct of this process


CalciumIIChloride CaCl2


iiiState two uses that the byproduct can be used for


As a drying agent in the school laboratory preparation of gases


In the Downs cellprocess for extraction of Sodium to lower the melting point of rock salt


ivWrite the chemical equation for the formation of the byproducts in the Solvay process


CaOH2 aq 2NH4Cl aq  CaCl2s  2NH3g  H2Ol


dIn an experiment to determine the  purity of Sodium carbonate produced in the Solvay process 215g of the sample reacted with exactly 400cm3 of 05M Sulphuric VIacid


iCalculate the number of moles of sodium carbonate that reacted


Na2CO3 aq H2SO4 aq  Na2SO4 aq CO2g  H2Ol


Mole ratio Na2CO3 H2SO4  11


Moles H2SO4  Molarity x Volume  05 x 400  002 Moles


1000 1000


Moles of Na2CO3  002 Moles


iiDetermine the  of sodium carbonate in the sample


Molar mass of Na2CO3  106g


Mass of Na2CO3  moles x Molar mass  002 x 106  212 g


of Na2CO3   212 g x 100  986047


e State two uses of soda ash


i during making glasslowering the melting point of mixture of sandSiO2 from 1650oC and CaO from 2500oC to around 1500oC


ii in softening hard water


iii in the manufacture of soapless detergents


iv swimming pool pH increaser


fThe diagram below shows a simple ammonia soda tower used in manufacturing sodium carbonate Use it to answer the questions that follow


iName the raw materials needed in the above process


Ammonia


Water


CarbonIVoxide


Limestone


Brine Concentrated sodium chloride


iiIdentify substance A


Ammonium chloride NH4Cl


iii Write the equation for the reaction taking place in


ITower


Chemical equation


CO2g  NaCl aq  H2Ol  NH3g  NaHCO3s  NH4Claq


II Production of excess carbon IVoxide


CaCO3 s  CaOs  CO2g


III The regeneration of ammonia


CaOH2 aq 2NH4Cl aq  CaCl2s  2NH3g  H2Ol


ivGive a reason for having the circular metal plates in the tower


To slow the downward flow of brine


To increase the rate of dissolving of ammonia


To increase the surface area for dissolution


vName the gases recycled in the process illustrated above


Ammonia gas  CarbonIVOxide and Water


2 Describe how you would differentiate between carbon IVoxide and carbonIIoxide using chemical method


Method I


Bubble both gases in lime waterCaOH2


white precipitate is formed if the gas is carbon IV oxide


No white precipitate is formed if the gas is carbon II oxide


Method II


ignite both gases


Carbon IV oxide does not burnignite


Carbon II oxide burn with a blue nonsooty flame


Method III


Lower a burning splint into a gas containing each gas separately


burning splint is extinguished if the gas is carbon IV oxide


burning splint is not extinguished if the gas is carbon II oxide


3Using Magnesium sulphateVIsolution describe how you can differentiate between a solution of sodium carbonate from a solution of sodium hydrogen carbonate


Add Magnesium sulphateVI solution to separate portions of a solution of sodium carbonate and sodium hydrogen carbonate in separate test tubes


White precipitate is formed in test tube containing sodium carbonate


No white precipitate is formed in test tube containing sodium hydrogen carbonate


Chemical equation


Na2CO3 aq MgSO4 aq  Na2SO4 aq  MgCO3s


white ppt


Ionic equation


CO32 aq  Mg2 aq  MgCO3s


2NaHCO3 aq MgSO4 aq  Na2SO4 aq  MgHCO32 aq


colourless solution


4 The diagram below shows a common charcoal burner Assume the burning take place in a room with sufficient supply of air


aExplain what happens around


iLayer A


Sufficientexcess air oxygen enter through the air holes into the burner It reacts withoxidizes Carbon to carbonIVoxide


Cs  O2g  CO2 g


iiLayer B


Hot carbonIVoxide rises up and is reduced by more carboncharcoal to carbon IIoxide


Cs  CO2g  2CO g


iiLayer C


Hot carbonIIoxide rises up and burns with a blue flame to be oxidized by the excess air to form carbonIVoxide


2CO g  O2g  2CO2g


bState and explain what would happen if the burner is put in an enclosed room


The hot poisonous toxic carbonIIoxide rising up will not be oxidized to CarbonIVoxide


cUsing a chemical test describe how you would differentiate two unlabelled black solids suspected to be charcoal and copperIIoxide


Method I


BurnIgnite the two substances separately


Charcoal burns with a blue flame


CopperIIoxide does not burn


Method II


Add dilute sulphuricVIacidNitricVacidHydrochloric acid separately


Charcoal does not dissolve


CopperIIoxide dissolves to form a colourless solution


5 Excess CarbonIIoxide was passed over heated copperIIoxide as in the set up shown below for five minutes


aState and explain the observations made in the combustion tube


Observation


Colour change from black to brown


Explanation


Carbon IIoxide reduces black copperIIoxide to brown copper metal itself oxidized to CarbonIVoxide


Chemical equation


COg  CuO s  Cus  CO2g


black brown


b iName the gas producing flame A


CarbonIIoxide


iiWhy should the gas be burnt


It is toxicpoisonous


iiiWrite the chemical equation for the production of flame A


2COg  O2g  2CO2g


cState and explain what happens when carbonIVoxide is prepared using Barium carbonate and dilute sulphuricVIacid


Reaction starts then stops after sometime producing smalllittle quantity of carbonIVoxide gas


Barium carbonate react with dilute sulphuricVIacid to form insoluble Barium sulphateVI that covercoat unreacted Barium carbonate stopping further reaction to produce more CarbonIVoxide


d Using dot  and crossx to represent electrons show the bonding in a molecule of


i CarbonIIoxide


ii CarbonIVOxide


e Carbon IVoxide is an environmental pollutant of global concern Explain


It is a green house gas thus causes global warming


It dissolves in water to form acidic carbonic acid which causes acid rain


fExplain using chemical equation why lime water is used to test for the presence of Carbon IV oxide instead of sodium hydroxide


Using lime watercalcium hydroxide


a visible white precipitate of calcium carbonate is formed that dissolves on bubbling excess Carbon IV oxide gas


Chemical equation


CaOH2aq  CO2 g  CaCO3 s  H2Ol


white precipitate


CaCO3 aq  H2Ol  CO2 g  CaHCO3 2 aq


Using sodium hydroxide


No precipitate of sodium carbonate is formed Both sodium carbonate and sodium hydrogen carbonate are soluble saltsdissolves


2NaOH aq  CO2 g  Na2CO3 s  H2Ol


No white precipitate


Na2CO3 s  H2Ol  CO2 g  2NaHCO3 s


gEthan12dioic acid and methanoic acid may be used to prepare small amount of carbonIIoxide in a school laboratory


i Explain the modification in the set up when using one over the other


Before carbonIIoxide is collected


when using methanoic acid no concentrated sodiumpotassium hydroxide is needed to absorb CarbonIVoxide


when using ethan12dioic acid concentrated sodiumpotassium hydroxide is needed to absorb CarbonIVoxide


iiWrite the equation for the reaction for the formation of carbonIIoxide from


IMethanoic acid


Chemical equation HCOOHaq  COg  H2Ol


II Ethan12dioic acid


Chemical equation HOOCCOOHaq  CO2gCOgH2Ol


hBoth carbonIIoxide and carbonIVoxide affect the environment Explain why carbonIIoxide is more toxicpoisonous


Both gases are colourlessdenser than water and odourless


CarbonIIoxide is preferentially absorbed by humanmammalian haemoglobin when inhaled forming stable carboxyhaemoglobin instead of oxyhaemoglobinThis reduces the free haemoglobin in the blood leading to suffocation and quick death CarbonIVoxide is a green house gas that increases global warming


CarbonIIoxide is readily oxidized to carbonIVoxide


6Study the flow chart below and use it to answer the questions that follow


aName


ithe white precipitate A


Calcium carbonate


ii solution B


Calcium hydrogen carbonate


iii gas C


CarbonIVoxide


iv white residue B


Calcium oxide


v solution D


Calcium hydroxidelime water


bWrite a balanced chemical equation for the reaction for the formation of


i the white precipitate A from solution D


Chemical equation


CaOH2aq  CO2 g  CaCO3 s  H2Ol


ii the white precipitate A from solution B


CaHCO32aq  CO2 g  CaCO3 s  H2Ol


iii solution B from the white precipitate A


CO2 g  CaCO3 s  H2Ol  CaHCO32aq


iv white residue B from the white precipitate A


CaCO3s  CO2 g  CaO s


iv reaction of white residue B with water


CaO s  H2Ol  CaOH2aq


INTRODUCTION TO SALTS


1a A salt is an ionic compound formed when the cation from a base combine with the anion derived from an acid


A salt is therefore formed when the hydrogen ions in an acid are replaced whollyfully or partiallypartly directly or indirectly by a metal or ammonium radical


b The number of ionizablereplaceable hydrogen in an acid is called basicity of an acid


Some acids are therefore


imonobasic acids generally denoted HX eg


HCl HNO3HCOOHCH3COOH


iidibasic acids  generally denoted H2X eg


H2SO4 H2SO3 H2CO3HOOCOOH


iiitribasic acids  generally denoted H3X eg


c Some salts are normal salts while others are acid salts


iA normal salt is formed when all the ionizable replaceable hydrogen in an acid is replaced by a metal or metallic ammonium radical


iiAn acid salt is formed when partportion the ionizable replaceable hydrogen in an acid is replaced by a metal or metallic ammonium radical


Table showing normal and acid salts derived from common acids


The table below show shows some examples of salts


d Some salts undergo hygroscopy deliquescence and efflorescence


i Hygroscopic salts compounds are those that absorb water from the atmosphere but do not form a solution


Some salts which are hygroscopic include anhydrous copperIIsulphateVI anhydrous cobaltIIchloride potassium nitrateV common table salt


iiDeliquescent salts compounds are those that absorb water from the atmosphere and form a solution


Some salts which are deliquescent include Sodium nitrateVCalcium chloride Sodium hydroxide IronIIchloride Magnesium chloride


iiiEfflorescent saltscompounds are those that lose their water of crystallization to the atmosphere


Some salts which effloresces include sodium carbonate decahydrate IronIIsulphateVIheptahydrate sodium sulphate VIdecahydrate


eSome salts contain water of crystallizationThey are hydratedOthers do not contain water of crystallization They are anhydrous


Table showing some hydrated salts


fSome salts exist as a simple salt while some as complex salts Below are some complex salts


Table of some complex salts


gSome salts exist as two salts in one They are called double salts


Table of some double salts


hSome salts dissolve in water to form a solution They are said to be soluble Others do not dissolve in water They form a suspensionprecipitate in water


Table of solubility of salts


13 Salts can be prepared in a school laboratory by a method that uses its solubility in water


Soluble salts may be prepared by using any of the following methods


iDirect displacementreaction of a metal with an acid


By reacting a metal higher in the reactivity series than hydrogen with a dilute acida salt is formed and hydrogen gas is evolved


Excess of the metal must be used to ensure all the acid has reacted


When effervescencebubbling fizzing has stopped excess metal is filtered


The filtrate is heated to concentrate then allowed to crystallize


Washing with distilled water then drying between filter papers produces a sample crystal of the salt ie


Ms  H2X  MXaq  H2g


Examples


Mgs  H2SO4aq  MgSO4 aq  H2g


Zns  H2SO4aq  ZnSO4 aq  H2g


Pbs  2HNO3aq  PbNO3 2aq  H2g


Cas  2HNO3aq  CaNO3 2aq  H2g


Mgs  2HNO3aq  MgNO3 2aq  H2g


Mgs  2HClaq  MgCl 2aq  H2g


Zns  2HClaq  ZnCl 2aq  H2g


iiReaction of an insoluble base with an acid


By adding an insoluble base oxidehydroxide to a dilute acid until no more dissolves in the acid a salt and water are formed Excess of the base is filtered off The filtrate is heated to concentrate allowed to crystallize then washed with distilled water before drying between filter papers eg


PbOs  2HNO3aq  PbNO3 2aq  H2O l


PbOH2s  2HNO3aq  PbNO3 2aq  2H2O l


CaO s  2HNO3aq  CaNO3 2aq  H2O l


MgO s  2HNO3aq  MgNO3 2aq  H2O l


MgO s  2HClaq  MgCl 2aq  H2O l


ZnO s  2HClaq  ZnCl 2aq  H2O l


ZnOH2s  2HNO3aq  ZnNO3 2aq  2H2O l


CuO s  2HClaq  CuCl 2aq  H2O l


CuO s  H2SO4aq  CuSO4aq  H2O l


Ag2Os  2HNO3aq  2AgNO3aq  H2O l


Na2Os  2HNO3aq  2NaNO3aq  H2O l


iii Reaction of insoluble soluble carbonate hydrogen carbonate with an acid


By adding an excess of a soluble insoluble carbonate or hydrogen carbonate to a dilute acid effervescence fizzingbubbling out of carbon IV oxide gas shows the reaction is taking place When effervescence fizzingbubbling out of the gas is over excess of the insoluble carbonate is filtered off The filtrate is heated to concentrate allowed to crystallize then washed with distilled water before drying between filter paper papers eg


PbCO3 s  2HNO3aq  PbNO3 2aq  H2O l CO2g


ZnCO3 s  2HNO3aq  ZnNO3 2aq  H2O l CO2g


CaCO3 s  2HNO3aq  CaNO3 2aq  H2O l CO2g


MgCO3 s  H2SO4aq  MgSO4aq  H2O l CO2g


Cu CO3 s  H2SO4aq  CuSO4aq  H2O l  CO2g


Ag2CO3 s  2HNO3aq  2AgNO3aq  H2O l  CO2g


Na2CO3 s  2HNO3aq  2NaNO3aq  H2O l  CO2g


K2CO3 s  2HClaq  2KClaq  H2O l  CO2g


NaHCO3 s  HNO3aq  NaNO3aq  H2O l  CO2g


KHCO3 s  HClaq  KClaq  H2O l  CO2g


iv neutralizationreaction of soluble basealkali with dilute acid


By adding an acid to a burette into a known volume of an alkali with 23 drops of an indicator the colour of the indicator changes when the acid has completely reacted with an alkali at the end point The procedure is then repeated without the indicator The solution mixture is then heated to concentrate allowed to crystallize washed with distilled water before drying with filter papers eg


NaOH aq  HNO3aq  NaNO3aq  H2O l


KOH aq  HNO3aq  KNO3aq  H2O l


KOH aq  HClaq  KClaq  H2O l


2KOH aq  H2SO4aq  K2SO4aq  2H2O l


2 NH4OH aq  H2SO4aq  NH42SO4aq  2H2O l


NH4OH aq  HNO3aq  NH4NO3aq  H2O l


iv Direct synthesiscombination


When a metal burn in a gas jar containing a non metal  the two directly combine to form a salt eg


2Nas  Cl2g  2NaCls


2Ks  Cl2g  2KCls


Mgs  Cl2g  Mg Cl2 s


Cas  Cl2g  Ca Cl2 s


Some salts once formed undergo sublimation and hydrolysis Care should be taken to avoid watermoisture into the reaction flask during their preparation Such salts include aluminum III chloride AlCl3 and iron III chloride FeCl3


1 Heated aluminium foil reacts with chlorine to form aluminiumIIIchloride that sublimes away from the source of heating then deposited as solid again


2Als  3Cl2g  2AlCl3 sg


Once formed aluminiumIIIchloride hydrolysesreacts with water vapour  moisture present to form aluminium hydroxide solution and highly acidic fumes of hydrogen chloride gas


AlCl3s 3H2 Og  AlOH3 aq  3HClg


2 Heated iron filings reacts with chlorine to form ironIIIchloride that sublimes away from the source of heating then deposited as solid again


2Fes  3Cl2g  2FeCl3 sg


Once formed  aluminiumIIIchloride hydrolysesreacts with water vapour  moisture present to form aluminium hydroxide solution and highly acidic fumes of hydrogen chloride gas


FeCl3s 3H2 Og  FeOH3 aq  3HClg


bInsoluble salts can be prepared by reacting two suitable soluble salts to form one soluble and one insoluble This is called double decomposition or precipitation The mixture is filtered and the residue is washed with distilled water then dried


CuSO4aq  Na2CO3 aq  CuCO3 s  Na2 SO4aq


BaCl2aq  K2SO4 aq  BaSO4 s  2KCl aq


PbNO32aq  K2SO4 aq  PbSO4 s  2KNO3 aq


2AgNO3aq  MgCl2 aq  2AgCls  MgNO32 aq


PbNO32aq  NH4 2SO4 aq  PbSO4 s  2NH4NO 3aq


BaCl2aq  K2SO3 aq  BaSO3 s  2KCl aq


14 Salts may lose their water of crystallization decompose melt or sublime on heating on a Bunsen burner flame


The following shows the behavior of some salts on heating gently or strongly in a laboratory school burner


aeffect of heat on chlorides


All chlorides have very high melting and boiling points and therefore are not affected by laboratory heating except ammonium chloride Ammonium chloride sublimes on gentle heating It dissociate into the constituent ammonia and hydrogen chloride gases on strong heating


NH4Cls NH4Clg NH3g  HClg


sublimation dissociation


beffect of heat on nitrateV


i Potassium nitrateVKNO3 and sodium nitrateVNaNO3 decompose on heating to form Potassium nitrateIIIKNO2 and sodium nitrateIIINaNO2 and producing Oxygen gas in each case


2KNO3 s  2KNO2s  O2g


2NaNO3 s  2NaNO2s  O2g


iiHeavy metal nitratesV salts decompose on heating to form the oxide and a mixture of brown acidic nitrogenIVoxide and oxygen gases eg


2CaNO32 s  2CaOs  4NO2g  O2g


2MgNO32s  2MgOs  4NO2g  O2g


2ZnNO32s  2ZnOs  4NO2g  O2g


2PbNO32s  2PbOs  4NO2g  O2g


2CuNO32s  2CuOs  4NO2g  O2g


2FeNO32s  2FeOs  4NO2g  O2g


iiiSilverInitrateV and mercuryII nitrateV are lowest in the reactivity series They decompose on heating to form the metalsilver and mercuryand the NitrogenIVoxide and oxygen gas ie


2AgNO3s  2Ag s  2NO2g  O2g


2HgNO32 s  2Hg s  4NO2g  O2g


ivAmmonium nitrateV and Ammonium nitrateIII decompose on heating to NitrogenIoxiderelightsrekindles glowing splint and nitrogen gas respectivelyWater is also formedie


NH4NO3s  N2O g  H2Ol


NH4NO2s  N2 g  H2Ol


c effect of heat on nitrateV


Only IronIIsulphateVI IronIIIsulphateVI and copperIIsulphateVI decompose on heating They form the oxide and produce highly acidic fumes of acidic sulphurIVoxide gas


2FeSO4 s  Fe2O3s  SO3g  SO2g


Fe2SO4 3s  Fe2O3s  SO3g


CuSO4 s  CuOs  SO3g


d effect of heat on carbonatesIV and hydrogen carbonateIV


iSodium carbonateIVand potassium carbonateIVdo not decompose on heating


iiHeavy metal nitrateIVsalts decompose on heating to form the oxide and produce carbonIVoxide gas Carbon IVoxide gas forms a white precipitate when bubbled in lime water The white precipitate dissolves if the gas is in excess eg CuCO3 s  CuOs  CO2g


CaCO3 s  CaOs  CO2g


PbCO3 s  PbOs  CO2g


FeCO3 s  FeOs  CO2g


ZnCO3 s  ZnOs  CO2g


iiiSodium hydrogen carbonateIV and Potassium hydrogen carbonateIVdecompose on heating to give the corresponding carbonate IV and form water and carbonIVoxide gas ie


2NaHCO 3s  Na2CO3s  CO2g  H2Ol


2KHCO 3s  K2CO3s  CO2g  H2Ol


iii Calcium hydrogen carbonate IV and Magnesium hydrogen carbonateIV decompose on heating to give the corresponding carbonate IV and form water and carbonIVoxide gas i e


CaHCO3 2aq  CaCO3s  CO2g  H2Ol


MgHCO3 2aq


NameClassAdm No


CHEMISTRY Practice balancing Chemical equations


Date doneDate markedDate revised


Balance the following chemical equations in the spaces provided on the question paper


Ca OH2aq  Cl2g  CaCl2aq  CaOCl2aq  H2Ol


Colddilute Calcium ChlorateI


Ca OH2aq Cl2g  CaCl2aq CaClO32aq H2Ol


HotConcentrated Calcium ChlorateV


NaOH  Cl2g  NaClO3 aq  NaClaq  3H2Ol Sodium Chlorate V


KOH  Cl2g  KClO3 aq KClaq  H2Ol Potassium Chlorate V


Ca OH2aq Cl2g  CaCl2aqCaOCl2aq H2Ol


NaCls  H2SO4l  NaHSO4aq  HClg


KCls  H2SO4l  KHSO4aq  HClg


CaOs  2H2Ol  CaOH2aq  H2Ol


CaOH2aq  Cl2 g  CaOCl2aq  H2Ol


HCls  NH3g  NH4Cls


Fes  2HClaq  FeCl2aq  H2 g


Zns  2HClaq  ZnCl2aq  H2 g


Mgs  2HClaq  MgCl2aq  H2 g


2Lis  2HClaq  2LiClaq  H2 g


CaCO3 s  2HClaq  CaCl2aq  H2Ol  CO2g


Colourless solution


1Chemical equation


Ionic equation


CaCO3 s  2Haq  Ca2aq  H2Ol  CO2g


2Chemical equation


Ag2CO3 s  2HClaq  2AgCls  H2Ol  CO2g


CoatsCover Ag2CO3


3Chemical equation


NaHCO3 s  HClaq  NaClaq H2Ol CO2g


colourless solution


NaHCO3 s  Haq  Naaq  H2Ol  CO2g


4Chemical equation


CuCO3 s  2HClaq  CuCl2aq H2Ol  CO2g


Blue Solution


CuCO3 s  2Haq Cu2aq  H2Ol  CO2g


5Chemical equation


FeCO3 s  2HClaq FeCl2aq H2Ol  CO2g


green solution


FeCO3 s  2Haq  Fe2aq  H2Ol CO2g


6Chemical equation


NH4 2CO3 s2HClaq 2NH4 ClaqH2Ol CO2g


Ionic equation


NH4 2CO3 s2H aq 2NH4  aqH2Ol CO2g


Chemical equation


NaOHaq  HClaq  NaClaq  H2Ol


OHaq  Haq  H2Ol


KOHaq  HClaq  KClaq  H2Ol


NH4OHaq  HClaq  NH4Claq  H2Ol


CuOs  2HCl aq  CaCl2aq  H2Ol


CuO s  2Haq  Cu2aq  H2Ol


CaOs  HCl aq  CaCl2 aq  H2O l


PbOs  2HCl aq  PbCl2 s  H2O l


No ionic equation


ZnOs  HCl aq  ZnCl2 aq  H2O l


ZnO s  2Haq  Zn2aq  H2Ol


H2g  Cl2g  2HClg


HClg  aq  HClaq


NH4Cls  HClg  NH3 g


Name ClassAdm No


Date doneDate markedDate revised


CHEMISTRY Form 2 Practice 1 Time 2 hours 80 marks


1 Study the information in the table below and answer the questions that follow The letters do not represent the actual symbols of the elements


i What chemical family do the elements A B and C belong 1mk


iiWrite the formula and electronic structure of an ion of B2mks


Formula


Electronic structure


iiiWhat type of bonding exist in2mks


atoms of C


chloride of B


ivWhat is ionization energy1mk


vExplain the following


1The 1st ionization energy is lower that the second ionization energy2mk


2The 1st ionization energy of B is lower that of C2mk


viWrite a chemical equation for the reaction of element B with


2Chlorine gas


3Steamwater vapour


2Study the information in the table below and answer the questions that follow  the letters do not represent the actual symbol of the substances


i Which substance would dissolve in water and could be separated from the solution by fractional distillation Give a reason 2mk


ii Which substances is a liquid at room temperature and when mixed with water two layers would be formed Explain 2mk


iii Which letter represents a substance that is gas at room temperature and which can be collected


I Over water Explain 2mk


II By downward displacement of air Density of air is 129 x 103gcm3 at room temperature


Explain 2mk


3 The grid below represents part of the periodic table The letters do not represent the actual symbols


a Select the most reactive


inonmetal 1mk


iimetal 1mk


b Write the formula of the compound consisting of 10mk


1D and Z only


2  X and Z only


3 Oxide of B


4 Carbonate of J


5 sulphate of D


6 Nitrate of B


7 Chloride of X


8 Sodium compound of E


9 Aluminium compound of Z


10 Hydrogen compound of G


c Select an element that can form an ion of charge 10mk


i 1


ii 1


iii 2


iv 3


v 3


d Which element has the least ionization energy Explain 2mks


f To which chemical family do the following elements belong 3mk


J


E


B


gWhen a piece of element G is placed in cold water it sinks to the bottom and effervescence of a colourless gas that burns explosively is produced Use a simple diagram to illustrate how this gas can be collected during this experiment 3mks


h An element K has relative atomic mass of 402It has two isotopes of masses 39 and 42 Calculate the relative abundance of each isotope 3mks


4 Balance the following chemical equation 6mk


1Ca OH2aq  Cl2g  CaCl2aq  CaOCl2aq  H2Ol


2NaOH  Cl2g  NaClO3 aq  NaClaq  3H2Ol


3NaCls  H2SO4l  NaHSO4aq  HClg


4CaOs  H2Ol  CaOH2aq  H2Ol


5Fes  HClaq  FeCl3aq  H2 g


6Zns  HClaq  ZnCl2aq  H2 g


5The diagram below shows a set up of apparatus for the school laboratory collection of dry chlorine gas


A Name 2mk


i Substance Q


ii Suitable drying agent L


b State a missing condition for the reaction to take place faster 1mk


c Moist red and blue litmus papers were dipped into the chlorine gas from the above set up State and explain the observations made 2mk


d Write the equation for the reaction taking place in the conical flask 1mk