The solubility of trona decrease with increase in temperature therefore solid crystals of trona grows on top of the lake upto or more than 30metres thick


A bucket dredger mines the trona which is then crushed mixed with lake liquor and pumped to washery plant where it is further refined to a green granular product called CRS


The CRS is then heated to chemically decompose trona to soda ashSodium carbonate


Chemical equation


2Na2CO3NaHCO32H2Os  3Na2CO3 s  CO2g  5H2Ol


Soda ashSodium carbonate is then stored It is called Magadi Soda Magadi Soda is used


make glass


for making soapless detergents


softening hard water


Common salt is colledcted at night because its solubility decreases with decrease in temperature It is used as salt lickfeed for animals


Summary flow diagram showing the extraction of Soda ash from Trona


23Extraction of common salt from Indian Ocean at Ngomeni in Kenya


Oceans are saltyThey contain a variety of dissolved salts about 77 being sodium chloride


During high tide water is collected into shallow pods and allowed to crystallize as evaporation takes placeThe pods are constructed in series to increase the rate of evaporation


At the final pod the crystals are scapped togetherpiled in a heap and washed with brine concentrated sodium chloride


It contains MgCl2 and CaCl2  MgCl2 and CaCl2are hygroscopic They absorb water from the atmosphere and form a solution


This makes table salt dampwet on exposure to the atmosphere


24Some water form lather easily with soap while others do not


Water which form lather easily with soap is said to be soft


Water which do not form lather easily with soap is said to be hard


Hardness of water is caused by the presence of Ca2 and Mg2 ions


Ca2 and Mg2 ions react with soap to form an insoluble grey white suspensionprecipitate called Scum curd Ca2 and Mg2 ions in water come from the water sources passing through rocks containing soluble salts of Ca2 and Mg2 eg Limestone or gypsum


There are two types of water hardness


atemporary hardness of water


bpermanent hardness of water


Temporary hardness of water is caused by the presence of dissolved calcium hydrogen carbonateCaHCO32 and magnesium hydrogen carbonateMgHCO32


When rain water dissolve carbonIV oxide from the air it forms waek carbonicIV acid ie


CO2g  H2Ol  H2CO3aq


When carbonicIV acid passes through limestonedolomite rocks it reacts to form soluble salts ie


In limestone areas H2CO3aq  CaCO3s  CaHCO32 aq


In dolomite areas H2CO3aq  MgCO3s  MgHCO32 aq


Permanent hardness of water is caused by the presence of dissolved calcium sulphateVICaSO4 and magnesium sulphateVIMg SO4 Permanent hardness of water is caused by water dissolving CaSO4 and MgSO4 from ground rocks


Hardness of water can be removed by the following methods


aRemoving temporary hardness of water


iBoilingheating


Boiling decomposes insoluble calcium hydrogen carbonateCaHCO32 and magnesium hydrogen carbonateMgHCO32 to insoluble CaCO3 and MgCO3 that precipitate away ie


Chemical equation


CaHCO32aq  CaCO3 s  CO2g  H2Ol


MgHCO32aq  MgCO3 s  CO2g  H2Ol


iiAdding sodium carbonate IV Washing soda


Since boiling is expensive on a large scale a calculated amount of sodium carbonate decahydrate Na2CO310H2O precipitates insoluble Ca2aq and Mg2aq ions as carbonates to remove both temporary and permanent hardness of water This a double decomposition reaction where two soluble salts form an insoluble and soluble salt ie


iwith temporary hard water


Na2CO3 aq  CaHCO3 2 aq  NaHCO3aq  CaCO3 s


Na2CO3 aq  MgHCO3 2 aq  NaHCO3aq  MgCO3 s


Ionic equation


CO32 aq  Ca2 aq  CaCO3 s


CO32 aq  Mg2 aq  MgCO3 s


iiwith permanent hard water


Na2CO3 aq  MgSO4 aq  Na2SO4 aq  MgCO3 s


Na2CO3 aq  CaSO4 aq  Na2SO4 aq  MgCO3 s


iiiAdding calcium IIhydroxideLime water


Lime watercalcium hydroxide removes only temporary hardness of water from by precipitating insoluble calcium carbonateIV


CaOH2 aq  CaHCO3 2 aq  2H2Ol  2CaCO3 s


Excess of Lime watercalcium hydroxide should not be used because it dissolves again to form soluble calcium hydrogen carbonateIV causing the hardness again


ivAdding aqueous ammonia


Aqueous ammonia removes temporary hardness of water by precipitating insoluble calcium carbonateIV and magnesium carbonateIV


Chemical equation


2NH3 aq  CaHCO3 2 aq  NH4 2CO3aq  CaCO3 s


2NH3 aq  MgHCO3 2 aq  NH4 2CO3aq  MgCO3 s


vUse of ionexchange permutit


This method involves packing a chamber with a resin made of insoluble complex of sodium salt called sodium permutit


The sodium permutit releases sodium ions that are exchanged with Mg2 and Ca2 ions in hard water making the water to be soft ie


Na2Xaq  Ca2 aq  Na aq  CaXs


Na2Xaq  Mg2 aq  Na aq  MgXs


Hard water containing Mg2 and Ca2


Ion exchange resin as


Sodium permutit


Na ions replace Mg2


and Ca2 to make the water soft


When all the Na ions in the resin is fully exchanged with Ca2 and Ng2 ions in the permutit column it is said to be exhausted


Brine concentrated sodium chloride solution is passed through the permutit column to regenerated recharge the column again


viDeionization demineralization


This is an advanced ion exchange method of producing deionized water Deionized water is extremely pure water made only of hydrogen and oxygen only without any dissolved substances


Deionization involve using the resins that remove all the cations by using


iA cation exchanger which remove absorb all the cations present in water and leave only H ions


iiAn anion exchanger which remove absorb all the anions present in water and leave only OH ions


The Haq and OH aq neutralize each other to form pure water


Chemical equation


Haq  OH aq  H2Ol


When exhausted the cation exchanger is regenerated by adding Haq from sulphuricVIacidhydrochloric acid


When exhausted the anion exchanger is regenerated by adding OHaq from sodium hydroxide


Advantages of hard water


Hard water has the following advantages


iCa2aq in hard water are useful in bone and teeth formation


ii is good for brewing beer


iiicontains minerals that cause it to have better sweet taste


ivanimals like snails and coral polyps use calcium to make their shells and coral reefs respectively


vprocessing mineral water


Disadvantages of hard water


Hardness of water


iwaste a lot of soap during washing before lather is formed


iicauses stainsblemishesmarks on clothesgarments


iiicauses fur on electric appliances like kettle boilers and pipes form decomposition of carbonates on heating This reduces their efficiency hence morehigher cost of powerelectricity


Sample revision questions


In an experiment soap solution was added to three separate samples of water The table below shows the volumes of soap solution required to form lather with 1000cm3 of each sample of water before and after boiling


a Which water sample is likely to be soft Explain 2mks


Sample II Uses little sample of soap


c Name the change in the volume of soap solution used in sample III 1mk


On heating the sample water become soft bcause it is temporary hard


2Study the scheme below and use it to aanswer the questions that follow


aWrite the formula of


iCation in solution K


iiwhite ppt L


iii colourless solution M


iv colourless solution N


vwhite ppt P


bWrite the ionic equation for the reaction for the formation of


iwhite ppt L


Al3aq  3OH aq  AlOH3s


cWhat property is illustrated in the formation of colourless solution M and N


Amphotellic


BASIC PRINCIPLES OF CHEMISTRY PRACTICALS


IntroductionRationale


Chemistry is a science


Chemistry practical all over the world is emphasized to all candidates sitting for a Chemistry paper


There are about seven main basic universal emphasis for all chemistry candidates sitting for a chemistry paper


iTitration volumetric analysis


iiThermochemistryenergy changes


iiiChemical kineticrates of reaction


ivQualitative analysisorganicinorganic


vSolubility and solubility curves


viFlame test


viiPhysical  general chemistry


Titrationvolumetric analysis


Titration is determining the end point of the burette contents that react with fixed usually 250cm3 from a pipette conical flask contents


As evidence of a titration actually done examining body require the candidate to record their burette readings before and after the titration


For KCSE candidates burette readings must be recorded in a titration table in the format provided by the Kenya National Examination Council


As evidence of all titration actually done Kenya National Examination Council require the candidate to record their burette readings before and after the titration to complete the titration table in the format provided


Sample Titration table format


Calculate the average volume of solution used


240  240  240  240 cm3


As evidence of understanding the degree of accuracy of burettes all readings must be recorded to a decimal point


As evidence of accuracy in carrying the out the titration candidates value should be within 02 of the school value


The school value is the teachers readings presented to the examining bodycouncil based on the concentrations of the solutions she presented to herhis candidates


Bonus mark is awarded for averaged reading within 01 school value as Final answer


Calculations involved after the titration require candidates thorough practice mastery on the


irelationship among the mole molar mass mole ratios concentration molarity


ii mathematical application of 1st principles


Very useful information which candidates forget appear usually in the beginning of the paper as


You are provided with


All calculation must be to the 4th decimal point unless they divide fully to a lesser decimal point


Never round off answers


bThermochemistryenergy changes


Energy is the capacity to do work which is measured in JoulesJ orkJ


Chemicalphysical changes take place with absorption Endothermic  or evolution production Exothermicof heat


Practically


iendothermic changes show absorption of heat by a fall  drop in temperature and has a H


iiexothermic changes show evolution production of heat by a rise in temperature and has a H


iiitemperature is measure using a thermometer


iva school thermometer is either coloured alcohol or colourlessmercury


v For accuracy candidates in the same practical session should use the same type of thermometer


vi fall  drop H in temperature is movement of thermometer level downward


vii rise H in temperature is movement of thermometer level upwards


Physical changes changes mainly involve meltingfreezingfussion and boiling vapourization


Chemical changes changes mainly involve displacement dissolving  neutralization


aEnergy changes in physical processes


Meltingfreezingfusionsolidification and boilingvaporizationevaporation are the two physical processes


Melting freezing point of pure substances is fixed constant


The boiling point of pure substance depends on external atmospheric pressure


Meltingfusion is the physical change of a solid to liquid Freezingfusion is the physical change of a liquid to solid


Meltingfreezingfusionsolidification are therefore two opposite but same reversible physical processes ie


A s Al


Boilingvaporizationevaporation is the physical change of a liquid to gasvapour Condensationliquidification is the physical change of gasvapour to liquid Boilingvaporizationevaporation and condensationliquidification are therefore two opposite but same reversible physical processes ie


B l Bg


Practically


Meltingliquidificationfusion involves heating a solid to weaken the strong bonds holding the solid particles together


Solids are made up of very strong bonds holding the particles very close to each other Kinetic Theory of matter


On heating these particles gain energyheat from the surrounding heat source to form a liquid with weaker bonds holding the particles close together but with some degree of freedom


Meltingfusion is an endothermic Hprocess that requireabsorb energy from the surrounding


iiFreezingfusionsolidification involves cooling a a liquid to reform rejoin the very strong bonds to hold the particles very close to each other as solid and thus lose their degree of freedom Kinetic Theory of matter


Freezing fusion  solidification is an exothermic Hprocess that require particles holding the liquid together to lose energy to the surrounding


iiiBoilingvaporizationevaporation involves heating a liquid to completely breakfree the bonds holding the liquid particles together


Gaseous particles have high degree of freedom Kinetic Theory of matter Boiling vaporization  evaporation is an endothermic H process that requireabsorb energy from the surrounding


ivCondensationliquidification is reverse process of boiling vaporization  evaporation


It involves gaseous particles losing energy to the surrounding to form a liquidIt is an exothermicH process


The quantity of energy required to change one mole of a solid to liquid or to form one mole of a solid from liquid at constant temperature is called molar enthalpylatent heat of fusion eg


H2Os  H2Ol H  60kJ mole1 endothermic process


H2Ol  H2Os H  60kJ mole1 exothermic process


The quantity of energy required to change one mole of a liquid to gasvapour or to form one mole of a liquid from gasvapour at constant temperature is called molar enthalpylatent heat of vapourization eg


H2Ol  H2Og H  440kJ mole1 endothermic process


H2Og  H2Ol H  440kJ mole1 exothermic process


To determine the boiling point of water


Procedure


Measure 20cm3 of tap water into a 50cm3 glass beaker Determine and record its temperatureHeat the water on a strong Bunsen burner flame and record its temperature after every thirty seconds for four minute


Sample results


Questions


1Plot a graph of temperature against timeyaxis


Sketch graph of temperature against time


2From the graph show and determine the boiling point of water


Note


Water boils at 100oC at sea levelone atmosphere pressure101300Pa but boils at below 100oC at higher altitudes


The sample results above are from Kiriari Girls High SchoolEmbu County on the slopes of Mt Kenya in Kenya Water here boils at 96oC


3Calculate the molar heat of vaporization of waterH 10O 16O


Working


Mass of water  density x volume  20 x 1 1000  002kg


Quantity of heat produced


mass of water x specific heat capacity of water x temperature change


002kg x 42 x  96  25   5964kJ


Heat of vaporization of one mole H2O


Quantity of heat


Molar mass of H2O


5964kJ  03313 kJ mole 1


To determine the melting point of candle wax


Procedure


Weigh exactly 50 g of candle wax into a boiling tube Heat it on a strongly Bunsen burner flame until it completely melts


Insert a thermometer and remove the boiling tube from the flame Stir continuously Determine and record the temperature after every 30seconds for four minutes


Sample results


Questions


bEnergy changes in chemical processes


iStandard enthalpyheat of displacement Hd


iiStandard enthalpyheat of neutralization Hn


iiiStandard enthalpyheat of solutiondissolution Hs


Standard enthalpyheat of displacement Hd


The molar standard enthalpyheat of displacement may be defined as the energyheat change when one mole of substance is displaced removed from its solution at standard conditions


Some displacement reactions


iZns  CuSO4aq  Cus  ZnSO4aq


Ionically Zns  Cu2aq  Cus  Zn2 aq


iiFes  CuSO4aq  Cus  FeSO4aq


Ionically Fes  Cu2aq  Cus  Fe2 aq


iiiPbs  CuSO4aq  Cus  PbSO4s


This reaction stops after some time as insoluble PbSO4s coatcover unreacted lead


ivCl2g  2NaBraq  Br2aq  2NaClaq


Ionically


Cl2g 2Br aq  Br2aq  2Cl aq


To determine the molar standard enthalpyheat of displacementHd of copper


Procedure


Place 20cm3 of 02M copperIIsulphateVIsolution into a 50cm3 plastic beakercalorimeter


Determine and record the temperature of the solution T1


Put all the Zinc powder provided into the plastic beaker Stir the mixture using the thermometer


Determine and record the highest temperature change to the nearest 05oC T2


Repeat the experiment to complete table 1 below


Sample results Table 1


Questions


1a Calculate


iaverage T


Average T  change in temperature in experiment I and II


50  60  55oC


iithe number of moles of solution used


Moles used  molarity x volume of solution  02 x 20  0004 moles


1000 1000


iii the enthalpy change H for the reaction


Heat produced H  mass of solutionm x specific heat capacity cx T


20 x 42 x 55  462 Joules  0462 kJ


ivState two assumptions made in the above calculations


Density of solution  density of water  1gcm3


Specific heat capacity of solutionSpecific heat capacity of water 42 kJ1kg1K


This is because the solution is assumed to be infinite dilute


2 Calculate the enthalpy change for one mole of displacement of Cu2 aq ions


Molar heat of displacement Hd  Heat produced H


Number of moles of fuel


0462 kJ  1155 kJmole1


3Write an ionic equation for the reaction taking place


Zns  Cu2aq  Cus  Zn2aq


4State the observation made during the reaction


Blue colour of copperIIsulphateVI fadesbecomes less bluecolourless


Brown solid deposits are formed at the bottom of reaction vessel beaker


5Illustrate the above reaction using an energy level diagram


8 The enthalpy of displacement Hd of copperIIsulphate VI solution is 12k6kJmole1Calculate the molarity of the solution given that 40cm3 of this solution produces 2204kJ of energy during a displacement reaction with excess iron filings


Number of moles  Heat produced H


Molar heat of displacement Hd


2204 kJ  00206moles


126 moles


Molarity of the solution  moles x 1000


Volume of solution used


00206moles x 1000  05167 M


Graphical determination of the molar enthalpy of displacement of copper


Procedure


Place 20cm3 of 02M copperIIsulphate VI solution into a calorimeter50cm3 of plastic beaker wrapped in cotton wooltissue paper


Record its temperature at time T 0Stir the solution with the thermometer carefully and continue recording the temperature after every 30 seconds


Place all the 15g Zinc powder provided after 1  minutes


Stir the solution with the thermometer carefully and continue recording the temperature after every 30 seconds for five minutes


Determine the highest temperature change to the nearest 05oC


Questions


1Show and determine the change in temperature T


From a well constructed graph T T2 T1 at 150 second by extrapolation


T  365  250  115oC


2Calculate the number of moles of copperII sulphateVIused given the molar heat of displacement of Cu2 aqions is 125kJmole1


Heat produced H  mass of solutionm x specific heat capacity cx T


20 x 42 x 115  966 Joules  0966 kJ


Number of moles  Heat produced H Molar heat of displacement Hd


0966 kJ  0007728moles


125 moles 7728 x 103moles


3 What was the concentration of copperIIsulphateVI in moles per litre


Molarity  moles x 1000


Volume used


7728 x 103moles x 1000  03864M


4The actual concentration of copper


II Sulphate VI solution was 04M Explain the differences between the two


Practical value is lower than theoretical


Heatenergy loss to the surrounding and that absorbed by the reaction vessel decreases T hence lowering the practical number of moles and molarity against the theoretical value


cStandard enthalpyheat of neutralization Hn


The molar standard enthalpyheat of neutralization Hn is defined as the energyheat change when one mole of a H H3Oions react completely with one mole of OH ions to form one mole of H2Owater


Neutralization is thus a reaction of an acid H H3Oions with a basealkali OH ions to form salt and water only


Strong acidsbasesalkalis are completelyfullywholly dissociated to many free ionsH H3O and OH ions


ii for strong acidbasealkali neutralization no energy is used to dissociate ionize since molecule is whollyfully dissociatedionized into free H H3O and OH ions


The overall energy evolved is comparatively higher  more than weak acidbase alkali neutralizations


For strong acidbasealkali neutralization the enthalpy of neutralization is constant at about 573kJmole1 irrespective of the acidbase used


This is because ionically


OHaq Haq  H2Ol


for all whollyfully completely dissociated acidbasealkali


Weak acidsbasesalkalis are partially dissociated to few free ionsH H3O and OH ions and exist more as molecules


Neutralization is an exothermicH process


The energy produced during neutralization depend on the amount of free ions H H3O and OHions existing in the acidbasealkali reactant


ifor weak acidbasealkali neutralizationsome of the energy is used to dissociate ionize the molecule into free H H3O and OH ions therefore the overall energy evolved is comparatively lowerlessersmaller than strong acid  base alkali neutralizations


Practically Hn can be determined as in the examples below


To determine the molar enthalpy of neutralization Hn of Hydrochloric acid


Procedure


Place 50cm3 of 2M hydrochloric acid into a calorimeter200cm3 plastic beaker wrapped in cotton wooltissue paper


Record its temperature T1


Using a clean measuring cylinder measure another 50cm3 of 2M sodium hydroxide


Rinse the bulb of the thermometer in distilled water


Determine the temperature of the sodium hydroxide T2


Average T2 andT1 to get the initial temperature of the mixture T3


Carefully add all the alkali into the calorimeter200cm3 plastic beaker wrapped in cotton wooltissue paper containing the acid


Stir vigorously the mixture with the thermometer


Determine the highest temperature change to the nearest 05oC T4 as the final temperature of the mixture


Repeat the experiment to complete table 1


iienthalpy change H of neutralization


H  mmass of solutionacidbase x cspecific heat capacity of solution x TT6  50 50 x 42 x 135  5670Joules  567kJ


iii the molar heat of neutralization the acid


Hn  Enthalpy change H  567kJ  567kJ mole1


Number of moles 01moles


cWrite the ionic equation for the reaction that takes place


OHaq Haq  H2Ol


dThe theoretical enthalpy change is 574kJ Explain the difference with the results above


The theoretical value is higher


Heatenergy loss to the surroundingenvironment lowers TT6 and thus Hn


Heatenergy is absorbed by the reaction vesselcalorimeterplastic cup lowers T and hence Hn


Sample results


aCalculate T6 the average temperature change T6  1325 1375  135 oC 2


bWhy should the apparatus be very clean


Impurities present in the apparatus reacts with acid base lowering the overall temperature change and hence Hn


cCalculate the


inumber of moles of the acid used


number of moles  molarity x volume  2 x 50  01moles 1000 1000


eCompare the Hn of the experiment above with similar experiment repeated with neutralization of a solution of


i potassium hydroxide with nitricV acid


The results would be the samesimilar


Both are neutralization reactions of strong acids and basesalkalis that are fully wholly dissociated into many free H  H3O and OH ions


ii ammonia with ethanoic acid


The results would be lowerHn would be less


Both are neutralization reactions of weak acids and basesalkalis that are partially partly dissociated into few free H  H3O and OH ions Some energy is used to ionize the molecule


fDraw an energy level diagram to illustrate the energy changes


Theoretical examples


1The molar enthalpy of neutralization was experimentary shown to be 515kJ per mole of 05M hydrochloric acid and 05M sodium hydroxide If the volume of sodium hydroxide was 20cm3 what was the volume of hydrochloric acid used if the reaction produced a 50oC rise in temperature


Working


Moles of sodium hydroxide  molarity x volume


05 M x 20cm3  001 moles


Enthalpy change H  Hn  515  0515kJ


Moles sodium hydroxide 001 moles


Mass of base  acid  Enthalpy change H in Joules


Specific heat capacity x T


0515kJ x 1000  245238g


42 x 5


Massvolume of HCl  Total volume  volume of NaOH


245238  200  45238 cm3


Graphically Hn can be determined as in the example below


Procedure


Place 8 test tubes in a test tube rack


Put 5cm3 of 2M sodium hydroxide solution into each test tube Measure 25cm3 of 1M hydrochloric acid into 100cm3 plastic beaker


Record its initial temperature at volume of base 0


Put one portion of the base into the beaker containing the acid


Stir carefully with the thermometer and record the highest temperature change to the nearest 05oC


Repeat the procedure above with other portions of the base to complete table 1 below


Complete the table to determine the change in temperature


Plot a graph of volume of sodium hydroxide against temperature change


From the graph show and determine


ithe highest temperature change T


T T2T1  highest temperatureT2 from extrapolating a correctly plotted graph less lowest temperature at volume of base0T1


287  220  67 0 oC


ii the volume of sodium hydroxide used for complete neutralization


From correctly plotted graph  1675 cm3


iii Calculate the number of moles of the alkali used


Moles NaOH  molarity x volume Vn


2 x 1675  00335 moles


ivCalculate H for the reaction


H  mass of solution mixture x c x T


250  1675 x 42 x 67


1174845 J  1174845 kJ


iii Calculate the molar enthalpy of the alkali


Hn  Heat change  1174845 kJ


number of moles 00335 moles


350699kJ mole1


i Standard enthalpyheat of solutiondissolution Hs


The standard enthalpy of solution Hs is defined as the energy change when one mole of a substance is dissolved in excess distilled water to form an infinite dilute solution


An infinite dilute solution is one which is too dilute to be diluted further


Practically the heat of solution is determined by dissolving a known mass volume of a solute in known massvolume of watersolvent and determining the temperature change


To determine the heat of dissolution of ammonium nitrateV


Place 100cm3 of distilled water into a plastic cupbeakercalorimeter


Put all the 50g of ammonium nitratevpotassium nitrateV ammonium chloride into the water


Stir the mixture using the thermometer and record the temperature change after every  minute to complete table1


Continue stirring throughout the experiment


aFrom the graph show and determine


ithe highest temperature change T


187  220  33 oC  not 33 oC


b Calculate the total energy change H during the reaction


H  mass of water x c x T


H100 x42 x 33 oC   1386 J   1386 kJ


c Calculate the number of moles of ammonium nitrate v used


Moles  mass  50  00625 moles


molar mass 80


dWhat is the molar heat of dissolution of ammonium nitrateV


H  Heat change   1386 kJ   22176 kJmole1


Number of mole 00625 moles


eWhat would happen if the distilled water is heated before experiment was performed


The ammonium nitrateV would take less time to dissolve


Increase in temperature reduces lattice energy causing endothermic dissollution to be faster


eIllustrate the above process on an energy level diagram


cChemical KineticRate of reaction


The rate of a chemical reaction can be defined as the time taken for a known amount of reactants to form known amount of products


Some reactions are too slow to be determined eg weathering others are instantaneous


The SI unit of time is seconds Minutes and hours are also common


Time is determined using a stop watchclock


Candidates using stop watchclock should learn to


iPress start button concurrently with starting off determination of a reaction using one hand each


iiPress stop button when the reaction is over


iiiRecord all times in seconds unless specified


ivPress reset button to begin another timing


vIgnore time beyond seconds for stop clockwatch beyond this accuracy


viAvoid accidental pressing of any button before recording


It can be very frustrating repeating a whole procedure


The following factors theoretically and practically alterinfluenceaffectdetermine the rate of a chemical reaction


aConcentration


bTemperature


An increase in concentration increases the rate the rate of reaction by reducing the time taken to completion


Theoretically increase in concentration is a decrease in distance between reacting particles which increases their collision frequency


Practically decreasing concentration is dilutingadding water


To demonstrate the effect of concentration on reaction rate


You are provided with


i sodium thiosulphate containing 40gdm 3 solution labeled A


ii 2M hydrochloric acid labeled solution B


You are required to determine the rate of reaction between solution A and B


Procedure


Measure 40cm3 of solution A into 100 cm3 glass beaker Place it on top of a penmark X Measure another 40cm3 of solution B Simultaneously put solution B into solution A and start off a stop watchclock Determine the time taken for the penmark X to be invisibleobscurred from above Repeat the procedure by measuring 35cm3 of solution B and adding 5cm3 of water Complete the table 1 below by using other values os solution B and water


Sample questions


iExplain the shape of the graph


Straight line graph from the origin


Decrease in concentration decreases the rate of reaction The higher the concentration of solution B the less time taken for mark x to be obscurredinvisible due to increased collision frequency between the reacting particles


iiFrom the graph determine the time taken for the mark to be invisible at 37cm3


At 37cm3 then 1t  1 37  0027


From a well plotted graph


1t  0027  162602 seconds


iiFrom the graph determine the volume of solution B at 100 seconds


100 seconds  1t  1  1000  001


At 1t  001  the volume of B  170cm3


iii State another factor that would alter the rate of the above reaction


Temperature


iii State another factor that would not alter the rate of the above reaction


Surface area


Pressure


Catalyst


b Temperature


An increase in temperature increases the rate of reaction


An increase of 10 oC10K practically doubles the rate of a chemical reactionreduces time of completion by 12


An increase in temperature increase the kinetic energy of reacting particles increasing their collision frequency


Practically increase in temperature involves heating the reactants


The results and presentation should be as in the effect of concentration


Increased temperature reverses the table I time results


ie less time as temperature increases


dQualitative analysis


Process of identifying unknown compounds


Compounds may be


iInorganic


iiorganic


Inorganic analysis


This involve mainly identification of ionic compounds containing cations and anions


Cations present in an ionic compounds are identified by adding a precipitating reagent that forms a precipitate unique to the cations in the compound


The main precipitating reagents used are


2M NaOH andor 2M NH3aq


When using 2M sodium hydroxide


iNo white precipitate is formed if K  and Na  ions are present


ii No white precipitate is formed if NH4 ions are present but a clourless gas with pungent smell of urine is produced which may not be recognized in a school laboratory examination setting


iiiWhite precipitate that dissolves  soluble in excess if Zn2 Pb2 Al3 ions are present


ivWhite precipitate that do not dissolvesinsoluble in excess if Ba2 Mg2 Ca2 ions are present


vBlue precipitate that do not dissolves insoluble in excess if Cu2 ions are present


viGreen precipitate that do not dissolvesinsoluble in excess if Fe2 ions are present


viiBrown precipitate that do not dissolvesinsoluble in excess if Fe3 ions are present


When using 2M aqueous ammonia


iNo white precipitate is formed if K  NH4 Na  ions are present


iiWhite precipitate that dissolves  soluble in excess if Zn2 ions are present


iiiWhite precipitate that do not dissolvesinsoluble in excess if Ba2 Mg2 Ca2 Pb2 Al3 ions are present


ivBlue precipitate that dissolves soluble in excess to form a deeproyal blue solution in excess if Cu2 ions are present


vGreen precipitate that do not dissolvesinsoluble in excess if Fe2 ions are present


viBrown precipitate that do not dissolvesinsoluble in excess if Fe3 ions are present


Anions present in an ionic compounds are identified by adding a specific precipitating reagent that forms a precipitate unique to the specific anions in the compound


iLeadIInitrateV solution


Lead forms insoluble PbSO4 PbSO3 PbCO3 PbS PbI2PbCl2


PbS is a black precipitate


PbI2 is a yellow precipitate


All the others are white precipitates


aIf a LeadIInitrateV solution is added to a substance solution compound


iA yellow ppt shows presence of I ions


iiA black ppt shows presence of S2 ions


iii A white ppt shows presence of SO42 SO32 CO32 Cl


bIf the white precipitate is added dilute nitricV acid


iIt dissolves to show presence of SO32 CO32


iiIt persistremains to show presence of SO42 Cl


cIf the white precipitate in bi is added acidified potassium manganateVII dichromateVI


i acidified potassium manganateVII is decolorized orange colour of acidified potassium dichromateVI turns to green to show presence of SO32


ii acidified potassium manganateVII is not decolorized orange colour of acidified potassium dichromateVI does not turn to greenremains orange to show absence of SO32 presence of CO32


cIf the white precipitate in bii is boiled


iIt dissolves to show presence of Cl


iiIt persistremains to show presence of SO42


iiBariumIInitrateVBarium chloride solution


BariumIInitrateVBarium chloride solution precipitates BaSO4 BaSO3  BaCO3 from SO42 SO32 CO32 ions


Inorganic qualitative analysis require continous practice discussion


Sample presentation of results


You are provided with solid Yaluminium IIIsulphateVIhexahydrateCarry out the following tests and record your observations and inferences in the space provided


1a Appearance


Observations inference 1mark


White crystalline solid Coloured ions Cu2  Fe2 Fe3 absent


bPlace about a half spatula full of the solid into a clean dry boiling tube Heat gently then strongly


Colourless droplets formed on the cooler Hydrated compoundcompound


part of the test tube containing water of crystallization


Solid remains a white residue


cPlace all the remaining portion of the solid in a test tube Add about 10cm3 of distilled water Shake thoroughly Divide the mixture into five portions


Observation Inference 1mark


Solid dissolves to form Polar soluble compound


a colourless solution Cu2  Fe2 Fe3 absent


iTo the first portion add three drops of sodium hydroxide then add excess of the alkali


White ppt soluble in excess Zn2  Pb2  Al3


iiTo the second portion add three drops of aqueous ammonia then add excess of the alkali


White ppt insoluble in excess Pb2  Al3


iiiTo the third portion add three drops of sodium sulphateVIsolution


No white ppt Al3


ivITo the fourth portion add three drops of LeadIInitrateIVsolution Preserve


White ppt CO32 SO42 SO32 Cl


IITo the portion in iv I above  add five drops of dilute hydrochloric acid


White ppt persistremains SO42 Cl


IIITo the portion in iv II above heat to boil


White ppt persistremains SO42


Organic analysis


This involve mainly identification of the functional group


i  C  C   C  C  C  C


R OH


iii R COOH  H


These functional groups can be identified by


iburninga substance which catches fire must reduce in amount


Candidates should not confuse burning with flame colorationtest


iiDecolorization of bromine waterchlorine wateracidified KMnO 4  to show presence of


C  C    C  C  and R  OH


iiiTurning orange acidified K 2 Cr 2 O 7 to green to show presence as in above


iiipH 123 for strongly acidic solutions pH 456 for weakly acidic solutions


ivTurning blue litmus paper red red litmus paper remaining red show presence of H ions


dFlame test


The colour change on a clear colourless Bunsen flame is useful in identifying some cations  metals


A very clean metallic spatula is recommended since dirt obscures changes the correct coloration distinct flame coloration of some compounds


ePhysical chemistry


Chemistry is a science subject that incorporate many scientific techniques


Examining bodycouncil require tabulated resultsdata from the candidate


This tabulated results is usually then put in a graph


The general philosophy of methods of presentation of chemistry practical data is therefore availability of evidence showing


iPractical donecomplete table


iiAccuracy of apparatus useddecimal point


iiiAccuracycare in doing experiment to get collect trendagainst teachers results


ivGraphical workuse of mathematical science


vCalculations Scientific mathematical integration


fSample practicals


Name ClassIndex No


Candidates signature


Date doneDate marked Date revised


CHEMISTRY Paper 3


PRACTICAL


PreKCSE Practice 1 2013


MARKS SCHEME


Instruction to Candidate


Write your name and index number in the spaces provided above


Sign and write the date of examination in the spaces provided above


Answer all questions in the spaces provided


Mathematical tables and electronic calculators may be used


All working must be clearly shown where necessary


This paper consist of 8 printed pages


Candidates should check the question paper to ascertain that all the pages are printed and indicated and that no questions are missin


For examiners use only


1You are provided with


isolution L containing 50g per litre of a dibasic organic acid H2X2H2O


iisolution M which is acidified potassium manganateVII


iiisolution N a mixture of sodium ethanedioate and ethanedioic acid


iv01M sodium hydroxide solution P


v10M sulphuricVI


You are required to


istandardize solution M using solution L


iiuse standardized solution M and solution P to determine the  of sodium ethanedioate in the mixture


Procedure 1


Fill the burette with solution M Pipette 250cm3 of solution L into a conical flask Heat this solution to about 70oCbut not to boilTitrate the hot solution L with solution M until a permanent pink colour just appears Shake thoroughly during the titration Repeat this procedure to complete table 1


Table 1


aCalculate the average volume of solution L used 1mk


200  200 200  200cm3


bGiven that the concentration of the dibasic acid is 005molesdm3determine the value of x in the formula H2X2H2O H10O160 1mark


Molar mass H2X2H2O  mass  litre


moles  litre


50glitre  100 g


H2X2H2O 100


X  100  2 x1  2 x 2 x1  2 x 16  100  34  62


c Calculate the number of moles of the dibasic acid H2X2H2O 1mark


Moles  molarity x pipette volume


005 x 25  000125  125 x10 3 moles


dGiven the mole ratio manganateVIIMnO4 acid H2X is 25 calculate the number of moles of manganateVII MnO4 in the average titre 1mark


Moles H2X  25 moles of MnO4


25 x 00125125 x10 2 moles  00005  50 x 10 4 moles


eCalculate the concentration of the manganateVIIMnO4 in moles per litre


Moles per litremolarity  moles x 1000


average burette volume


0000550 x 10 4moles x 1000  002083 moles l1  M


Procedure 2


With solution M still in the burette pipette 250cm3 of solution N into a conical flask Heat the conical flask containing solution N to about 70oCTitrate while hot with solution M Repeat the experiment to complete table 2


Table 2 2marks


125  125  125  125 cm3


bCalculations


iHow many moles of manganateVIIions are contained in the average volume of solution M used 1mark


Moles  molarity of solution M x average burette volume


002083 molesl1 M x 125  000026  26 x 104 moles


iiThe reaction between manganateVIIions and ethanedioate ions that reacted with is as in the equation


2MnO4 aq  5C2O42 aq  16H aq  2Mn2aq  10CO2g  8H2Ol


Calculate the number of moles of ethanedioate ions that reacted with manganate VII ions in the average volume of solution M 1mark


From the stoichiometricionic equation


mole ratio MnO4 aq C2O42 aq  25


moles C2O42  52 moles MnO4


52 x 000026  25 x 103 moles


000065  65 x104 moles


iiiCalculate the number of moles of ethanedioate ions contained in 250cm3 solution N 1mark


25cm3 pipette volume  000065 65 x104 moles


250cm3  00065 65 x103 moles x 250  00065  65 x103 moles


Procedure 3


Remove solution M from the burette and rinse it with distilled water Fill the burette with sodium hydroxide solution P Pipette 25cm3 of solution N into a conical flask and add 23 drops of phenolphthalein indicator Titrate this solution N with solution P from the burette Repeat the procedure to complete table 3


Table 3


2 mark


aCalculate the average volume of solution L used 1mk


125  125  125  125 cm3


bCalculations


iHow many moles of sodium hydroxide solution P were contained in the average volume 1mark


Moles  molarity of solution P x average burette volume


01 molesl1 x 249  000249  249 x 103 moles


iiGiven that NaOH solution P reacted with the ethanedioate ions from the acid only and the equation for the reaction is


2NaOH aq  H2C2O4 aq  Na2C2O4g  2H2Ol


Calculate the number of moles of ethanedioic acid that were used in the reaction1 mk


From the stoichiometric equationmole ratio


NaOHaq H2C2O4 aq  21


moles H2C2O4  12 moles NaOH


12 x 000249  249 x 103 moles


00012451245 x103 moles


iiiHow many moles of ethanedioic acid were contained in 250cm3 of solution N 1mark


25cm3 pipette volume  00012451245 x103


250cm3  00012451245 x103 moles x 250 25


0012451245 x102 moles


iiiDetermine the  by mass of sodium ethanedioate in the mixture


H 10O160C120 and total mass of mixture 20 g in 250cm3 solution 1mark


Molar mass H2C2O4  900g


Mass of H2C2O4 in 250cm3


moles in 250cm3 x molar mass H2C2O4


0012451245 x102 moles x 900


by mass of sodium ethanedioate


Mass of mixture  mass of H2C2O4 x 100


Mass of mixture


20  11205 g  43975


2 You are provided with 50 g solid B You are to determine the molar mass of solid B


Procedure


Place 100cm3 of liquid L into a plastic beaker Determine its temperature and record it at time  0 in Table 2 below Stir continuously using the thermometer and record the highest temperature change to the nearest 05oC after every 30 seconds After 120 seconds add all solid B Continue stirring and recording the temperature to complete table 2


Table 2


aPlot a graph of temperature against timexaxis3marks


bFrom the graph show and determine 2 mark


i the highest temperature change T


T  T2 T1  134 20  66o C


Note T is not  66oC


ii the temperature of the mixture at 130 seconds


From extrapolation at 130 seconds  192 oC


iiithe time when all the solid first dissolved


From extrapolation of the lowest temperature  220 Seconds


d Calculate the heat change for the reactionAssume density of liquid L is 10gcm3  specific heat capacity is 42Jkg1K11mark


H  mass of liquid L x c x T 100 x 42 x 66   2772 J   2772 kJ


e Given the molar enthalpy of dissolution of Solid B in liquid L is  22176kJ mole1determine the number of moles of B used1mark


Moles of B  H   2772 kJ  0125 moles


Hs  22176kJ mole1


fCalculate the molar mass of B 1mark


Molar mass of B  Mass used  50 40 g


Moles used 0125 moles


3aYou are provided with solid Y Carry out the following tests and record your observations and inferences in the space provided


i Appearance


Observations inference 1mark


White crystalline solid Coloured Fe2 Fe3  Cu2 ions absent


iiPlace about a half spatula full of the solid into a clean dry boiling tube Heat gently then strongly


Colourless droplets forms on the cooler parts of Hydrated compoundsalt


test tube


Solid remain white


iiPlace all the remaining portion of the solid in a test tube Add about 10cm3 of distilled water Shake thoroughly Divide the mixture into five portions


Observation Inference 1mark


Solid dissolves to form a colourless solution Coloured Fe2  Fe3  Cu2 ions absent


I To the first portion add three drops of universal indicator 1mark


Observation Inference


pH 4 weakly acidic solution


IITo the second portion add three drops of aqueous ammonia then add excess of the alkali


White ppt insoluble in excess Al3  Pb2


IIITo the third portion add three drops of sodium sulpide solution


No black ppt Al3


IVTo the fourth portion add three drops of acidified LeadIInitrateIVsolution Heat to boil


White ppt  persistremains on boiling SO42


bYou are provided with solid P Carry out the following tests and record your observations and inferences in the space provided


iPlace a portion of solid P on a clean metallic spatula and introduce it on a Bunsen flame


12 mark


Solid burns with a yellow sooty flame C C  C C bonds


iiAdd all the remaining solid to about 10cm3 of water in a test tube and shake well Divide the mixture into 4 portions 12 mark


Solid dissolves to form a clourless solution Polar organic compound


I To the 1st portion test with litmus papers 12 mark


Red litmus paper remain red H ions Blue litmus paper turn blue


II To the 2nd portion add a little sodium hydrogen carbonate12 mark


Effervescencefizzingbubbles H ions


Colourless gas produced


IIITo the 3rd portion and three drops of solution M Warm12 mark


Acidified KMnO4 is decolorized R OH C C  C C bonds


solution M is decolorized IVTo the 4th portion add three drops of bromine water 12marks Bromine water is decolorized C C  C C bonds


2333 CHEMISTRY


PreKCSE 2013


Practice 1


Moi High SchoolMbiruri


Requirements for each Candidates


005 M Oxalic acid labeled Solution L


001M Potassium manganate VII labeled Solution M


003M oxalic acid labeled Solution N


01M Sodium hydroxide labeled Solution P


10M sulphuricVIacid


15 0cm3 distilled water labeled Liquid L


50cm3 burette


25cm3 pipette


Two clean conical flasks


Pipette filler


10 1100C Thermometer


Stop watchclock


200cm3 clean beaker


54g ammonium chloride80g Ammonium nitrateV labeled Solid B weighed accurately


About 20 g of hydrated Aluminium sulphate labeled Solid Y


About 20g of Citric acid labeled Solid P


One boiling tube


Six clean dry test tubes


Pair of litmus papersred and blue


Clean metallic spatula


Access to bench reagentsapparatus


Means of heating


2M aqueous ammonia


01M acidified LeadIInitrateV


Bromine water


01M sodium sulphide


About 01g Sodium hydrogen carbonate


Universal indicator solution


pH chart


Name Index Number


2333 Candidates signature


CHEMISTRY Date


Paper 3


PRACTICAL


Practice 2012


214 hours


You are provided with


Solution A containing an oxidizing agent A


Solution B 005M aqueous sodium thiosulphate


Solution C containing a reducing agent C


Aqueous Potassium iodide


Solution D starch solution


You are required to determined the


Concentration of solution A


Rate of reaction between the oxidizing agent A and the reducing agent C


Procedure 1


Using a pipette and pipette filter place 250cm3 of solution A into a 250ml conical flask


Meassure 10cm3 of aqueous potassium iodide and add it to solution A in the conical flask


Shake the mixture Add 10cm3 of 2M sulphuricVIacid to the mixture and shake


Fill a burette with solution B and use it to titrate the mixture in the conical flask until it just turns orange yellowAdd 2cm3 of solution D to the mixture in the conical flask Shake thoroughly Continue titrating until the mixture just turns colourless Record your results in table 1 below


Repeat the procedure and complete table 1Retain the remainder of solution A and D for use in procedure II


Table I


aCalculate the


i average volume of solution B used1mk


200  200 200   200 cm3


iinumber of moles of sodium thisulphate1mk


Moles  molarity x burette volume


005 x200   0001  10 x103  moles


bGiven that one mole of A reacts with six moles of sodium thiosulphate calculate the


inumber of moles of A that were used 1mk


Mole ratio AB  16


Moles A  0001  10 x103 moles  00001616 x104  moles


iiconcentration of solution A in moles per litre2mk


Molarity of solution A  moles x 1000


Pipette volume


00001616 x104 moles x1000   000880 x104 M


Procedure II


Label six test tubes as 1234 5 and 6 and place them on a test tube rack


Using a clean burette measure the volumes of distilled water as shown in table 2 into the labeled test tubes


Using a burette measure the volumes of solution A shown in table 2 into each of the test tubes


Clean the burette and rinse it with about 5cm3 of solution C


Using the burette measure 5cm3 of solution C and place it into a 100ml beaker


Using a 10ml measuring cylinder measure 5cm3 of solution D and add it to the beaker containing solution C Shake the mixture


Pour the contents of test tube number 1 to the mixture in the beaker and immediately start off stop watchclock Swirl the contents of the beakerRecord the time taken for a blue colour to appear in table 2


Repeat steps 5 to7 using the contents of testtube 2345 and 6


Complete table 2 by computing Rate  1 S1


Time


Table 2Sample results


Plot a graph of rateyaxis against volume of solution A3mk


Sketch graph of rate against time


bWhat time would be taken for the blue colour to appear if the experiment was repeated using 4cm3 of distilled water and 6cm3 of solution A2mk


From a correctly plotted graph


1t at 6cm3  00125   t  100125  80seconds


2 You are provided with solid E Carry out the experiments below Write your observations and inferences in the spaces provided


aPlace all solid in a boiling tube Add 20cm3 of distilled water and shakeuntil all the solid dissolvesLabel the solution as solution EUse solution E for experiment iand ii


iTo 2cm3 of solution E in a test tube in each of experiment IIIIII and IV add


I two drops of aqueous sodium sulphateVI


Observation1mk Inferences1mk


White precipitate Pb2 Ba2 Ca2


IIfive drops of aqueous sodium chloride


Observations 1mk Inferences1mk


White ppt Ca2 Ba2


IIItwo drops of barium chloride


Observations1mk Inferences1mk


No white ppt SO42 SO32 CO32 IV two drops of leadIInitrateV


No white ppt Cl


ii To 2cm3 of solution E in a test tube add 5 drops of aqueous sodium hydroxide Add the piece of aluminium foil provided to the mixture and shake Warm the mixture and test any gas produced with both blue and red litmus papers


Blue litmus paper remain blue


Red limus paper turn blue NO3


Effervescence fizzing bubbles


Note


Solid E is Calcium nitrateV  Barium nitrateV


3You are provided with solid F Carry out the following testWrite your observations and inferences in the spaces provided


aPlace all of solid F in a boiling tube Add about 20cm3 of distilled water and shake until all the solid dissolves Label the solution as solution F


Add about half of the solid sodium hydrogen carbonate provided to 2cm3 of solution F


Observations1mk Inferences 1mk


No effervescencefizzing H absent


biAdd about 10cm3 of dilute hydrochloric acid to the rest of solution F in the boiling tube Filter the mixture Wash the residue with about 2cm3 of distilled waterDry the residue between filter papers Place about one third of the dry residue on a metallic spatula and burn it in a Bunsen burner flame


Solid burns with a yellow sooty flame C C  C C


iiPlace all the remaining residue into a boiling tube Add about 10cm3 of distilled water and shake thoroughly Retain the mixture for the tests in c


Observations 12mk Inferences12mk Solid dissolves to a colourless solution Polar compound


cDivide the mixture into two portions


ito the first portion add the rest of the solid sodium hydrogen carbonate


Observations 1mk Inferences1mk Effervescencefizzing H


iito the second portion add two drops of bromine water


Observations 1mk Inferences1mk Bromine water decolorized C C  C C bonds


CHEMISTRY OF METALS


aIntroduction to metals


The rationale of studying metals cannot be emphasizedSince ages the world over metals like gold and silver have been used for commercial purposes


The periodicity of alkali and alkaline earth metals was discussed in year 2 of secondary school education This topic generally deals with


aNatural occurrence of the chief ores of the most useful metals for industrial commercial purposes


bExtraction of these metals from their ores for industrial commercial purposes


cindustrial commercial uses of these metals


dmain physical and chemical properties characteristic of the metals


The metals given detailed emphasis here are Sodium Aluminium Iron Zinc Lead and Copper


The main criteria used in extraction of metals is based on its position in the electrochemicalreactivity series and its occurrence on the earths crust


Natural occurrence


Sodium naturally occurs as


iBrinea concentrated solution of sodium chlorideNaClaq in salty seas and oceans


iiRock saltsolid sodium chlorideNaCls


iiiTronasodium sesquicarbonateNaHCO3Na2CO32H2O especially in lake Magadi in Kenya


ivChile saltpetersodium nitrateNaNO3


bi


Extraction of Sodium from brineManufacture of Sodium hydroxideThe flowing mercury cathode cell TheCasterKeller process


IRaw materials


i Brineconcentrated solution of sodium chloride NaCl aq from salty seas and oceans


iiMercury


iiiWater from riverlakes


II Chemical processes


Salty lakes seas and oceans contain large amount of dissolved sodium chloride NaCl aq solution


This solution is concentrated to form brine which is fed into an electrolytic chamber made of suspended Carbon graphitetitanium as the anode and a continuous flow of Mercury as the cathodeNote


Mercury is the only naturally occurring known liquid metal at room


temperature and pressure


Questions


I Write the equation for the decomposition of the electrolyte during the electrolytic process


H2Ol Haq  OHaq


NaClaq Naaq  Claq


II Name the ions present in brine that moves to the


iMercury cathode Haq  Naaq


iiTitaniumgraphite OHaq Claq


III Write the equation for the reaction that take place during the electrolytic process at the


Cathode 2Naaq  2e 2Nas


Anode 2Claq Cl2g  2e


Note


iConcentration of 2Claq ions is higher than OH ions causing overvoltage thus blocking OH ions from being discharged at the anode


iiConcentration of Naaq ions is higher than H ions causing overvoltage thus blocking H ions from being discharged at the cathode


IV Name the products of electrolysis in the flowing mercurycathode cell


iMercury cathode Sodium metal as grey soft metalsolid


iiTitaniumgraphite Chlorine gas as a pale green gas that turns moist bluered litmus papers red then bleaches both Chlorine gas is a very useful byproduct in


imaking PVCpolyvinylchloridepolychloroethene pipes


iichlorinationsterilization of water to kill germs


iiibleaching agent


ivmanufacture of hydrochloric acid


Sodium produced at the cathode immediately reacts with the mercury at the cathode forming sodium amalgamNaHg liquid that flow out of the chamber


Nas  Hgl Na Hg l


Sodium amalgam is added distilled water and reacts to form sodium hydroxide solution free mercury and Hydrogen gas


2Na Hg l  2H2Ol 2NaOH aq  2Hgl  H2g


Hydrogen gas is a very useful byproduct in


imaking ammonia gas in the Haber process


iimanufacture of hydrochloric acid


iiiin weather balloons to forecast weather


ivas rocket fuel


As the electrolysis of brine continues the concentration of Clions decreases and oxygen gas start being liberated Continuous feeding of the electrolyte is therefore very necessary


IIIUses of sodium hydroxide


The sodium hydroxide produced is very pure and is used mainly in iMaking soapy and soapless detergents


iimaking cellulose acetaterayon


IV Diagram showing the Manufacture of Sodium hydroxide from the flowing Mercurycathode cell


V Environmental effects of Manufacture of Sodium hydroxide from the flowing Mercurycathode cell


1Most of the Mercury used at the cathode is recycled


ito reduce the cost because mercury is expensive


iito reduce pollution because mercury kills marine life


iiibecause it causes chromosomalgenetic mutation to human beings


2Chlorine produced at the anode


ihas a pungent irritating smell that causes headache to human beings


iibleaches any wet substance


iiidissolves water to form both hydrochloric acid and chloricIacid


Both cause marine pollution and stomach upsets


bii


Extraction of sodium from rock saltThe Downs cellprocess


I Raw materials


iRock saltsolid sodium chloride


iicalciumIIchloride


II Chemical processes


Rock salt solid sodium chloride is heated to molten state in a chamber lined with fire bricks on the outside


Sodium chloride has a melting point of about 800oC A little calcium II chloride is added to lower the melting point of the electrolyte to about 600oC


The molten electrolyte is the electrolyzed in a carbon graphite anode suspended at the centre and surrounded by steel cathode


Questions


I Write the equation for the decomposition of the electrolyte during the electrolytic process


NaCll Nal  Cll


Note In absence of water the ions are in liquid state


II Name the ions present in molten rock salt that move to the


iSteel cathode Nal


iiCarbon graphite anode Cll


III Write the equation for the reaction that take place during the electrolytic process at the


iSteel cathode


2Nal  2e 2Nal


iiCarbon graphite anode


2Cll Cl2g  2e


IV Name the products of electrolysis in the Downs cell at


iCathode


Grey solid Sodium metal is less dense than the molten electrolyte and therefore float on top of the cathode to be periodically tapped off


iiAnode


Pale green chlorine gas that turns moistdampwet bluered litmus papers red then bleachesdecolorizes both Chlorine gas is again a very useful byproduct in


imaking PVCpolyvinylchloridepolychloroethene pipes


iichlorinationsterilization of water to kill germs


iiibleaching agent


ivmanufacture of hydrochloric acid


A steel diaphragmgauze is suspended between the electrodes to prevent recombination of sodium at the cathode and chlorine gas at the anode back to sodium chloride


III Diagram showing the Downs cellprocess for extraction of sodium


IV Uses of sodium


1Sodium vapour is used as sodium lamps to give a yellow light in street lighting


2Sodium is used in making very useful sodium compounds like


iSodium hydroxideNaOH


iiSodium cyanideNaCN


iiiSodium peroxideNa2O2


3An alloy of Potassium and Sodium is used as coolant in nuclear reactors


V Environmental effects of Downs cell


1Chlorine produced at the anode


ihas a pungent irritating smell that causes headache to human beings


iibleaches any wet substance


iiidissolves water to form both hydrochloric acid and chloricIacid


Both cause marine pollution and stomach upsets


2Sodium metal rapidly react with traces of water to form alkaline Sodium hydroxideNaOHaqsolution This raises the pH of riverslakes killing aquatic lifein case of leakages


VI Test for presence of Na


If a compound has Na ions in solidmoltenaqueous state then it changes a nonluminous clearcolourless flame to a yellow coloration but does not burn


Experiment


Scoop a portion of sodium chloride crystalssolution in a clean metallic spatula Introduce it to a clear colourless Bunsen flame


Practice


iCalculate the time taken in hours for 230kg of sodium to be produced in the Downs cell when a current of 120kA is used


iiDetermine the volume of chlorine released to the atmosphere Na230Faraday constant96500CI mole of a gas 24dm3 at rtp


Working


Equation at the cathode


2Na l  2e  2Nal


2 mole of electrons  2 Faradays  2 x 96500 C deposits a mass  molar mass of Na  230g thus


230 g  2 x 96500 C


230 x 1000g  230 x 1000 x 2 x 96500


1930000000  193 x 10 9C


Timet in seconds  Quantity of electricity CurrentI in amperes


Substituting


120 x 1000A


160833333seconds  2680556 minutes


Volume of Chlorine


Method 1


Equation at the anode


2 Cl l  Cl2g  2e


From the equation


2 moles of electrons  2 Faradays 2 x 96500C


2 x 96500C  24dm3


1930000000  193 x 10 9C1930000000  193x10 9C x 24


2 x 96500C


Volume of Chlorine  240000dm3 24 x 105dm3


Method 2


Equation at the anode Cl l  Cl2g  2e


Mole ratio of products at Cathode anode  11


Moles of sodium at cathode 230 x 1000 g 10000moles


10000moles of Na  10000moles moles of Chlorine


1 moles of Chlorine gas  24000cm3


10000moles of Chlorine  10000 x 24


240000dm3  24x 105dm3


Method 3


Ratio of Faradays of products at Cathode anode  22


2 x 96500C produce 24000cm3 of chlorine gas Then 1930000000  193 x 10 9C


1930000000  193 x 10 9C x24  240000dm3


2 x 96500


iijThe sodium metal produced was reacted with water to form 25000dm3 solution in a CasterKeller tank


aCalculate the concentration of the resulting solution in moles per litre


bThe volume of gaseous products formed at stp1 mole of gas 224 dm3 at stp


Chemical equation at CasterKeller tank


2Nas  2H2Ol  2NaOHaq  H2 g


Mole ratio NaNaOH  2  2  11


Moles Na 10000moles10000moles of NaOH


25000dm3 10000moles of NaOH


1dm3  10000 x 1  04M  04 molesdm3


Mole ratio Na H2 g  2  1


Moles Na  10000moles  5000moles of H2 g


Volume of H2 g  moles x molar gas volume at stp  5000moles x 224 dm3


ivThe solution formed was further diluted with water for a titration experiment 250 cm3 of the diluted solution required 200cm3 of 02M sulphuricVIacid for complete neutralization Calculate the volume of water added to the diluted solution before titration


Chemical equation


2NaOHaq  H2SO4aq  Na2SO4aq  H2Ol


Moles ratio NaOH  H2SO4  2  1


Moles ratio H2SO4  molarity x volume  02M x 20


1000 1000


40 x 103 moles


Moles NaOH  2 x 40 x 103 moles 80 x 103 moles


Molarity of NaOH Moles x 1000 80 x 103 moles x 1000


volume 25


016 molesdm3 M


Volume used during dilution


C1V1  C2V2  04M x V1  016 M x 25


016 M x 25  10cm3


a Below is a simplified diagram of the Downs Cell used for the manufacture of sodium Study it and answer the questions that follow


iWhat material is the anode made of Give a reason 2 mks


Carbon graphiteTitanium


This because they are cheap and inertdo not influenceaffect the products of electrolysis


ii What precaution is taken to prevent chlorine and sodium from re combination  1 mks


Using a steel gauzediaphragm separating the cathode from anode


iii Write an ionic equation for the reaction in which chlorine gas is formed  1mk


2Cll  Cl2g  2e


b In the Downs process used for manufacture of sodium a certain salt is added to lower the melting point of sodium chloride from about 8000C to about 6000C


i Name the salt that is added 1mk


Calcium chloride


ii State why it is necessary to lower the temperature1mk


To reduce the cost of production


c Explain why aqueous sodium chloride is not suitable as an electrolyte for the manufacture of sodium in the Downs process 2mk


The sodium produced react explosivelyvigorously with water in the aqueous sodium chloride


d Sodium metal reacts with air to form two oxide Give the formulae of two oxides  1mk


Na2O Sodium oxidein limited air


Na2O2 Sodium peroxidein excess air


aNatural occurrence


Aluminium is the most common naturally occurring metal It makes 7 of the earths crust as


iBauxite ore Hydrated aluminium oxideAl2O32H2O


iiMica orePotassium aluminium silicateK2Al2Si6O16


iiiChina clay ore aluminium silicate Al2Si6O16


ivCorrundumAnhydrous aluminium oxideAl2O3


bExtraction of aluminium from BauxiteHalls cellprocess


The main ore from which aluminium is extracted is Bauxite ore hydrated aluminium oxideAl2O32H2O


The ore is mined by opencaste mining methodquarrying where it is scooped together with silicasandsiliconIVoxide SiO2 and soil ironIIIoxide Fe2O3 as impurities


The mixture is first dissolved in hot concentrated sodiumpotassium hydroxide solution


The alkalis dissolve both bauxite and siliconIVoxide


This is because bauxite is amphotellic while siliconIVoxide is acidic


IronIIIoxide Fe2O3 is filtered of removed as a residue


CarbonIVoxide is bubbled into the filtrate to precipitate aluminium III hydroxide AlOH3 as residue


The aluminium III hydroxide AlOH3 residue is filtered off Silicon IVoxide remain in the solution as filtrate Aluminium III hydroxide AlOH3 residue is then heated to form pure aluminium IIIoxideAl2O3


2AlOH3 s Al2O3 s  3H2Ol


Pure aluminium IIIoxide Al2O3 has a very high melting point of 2015oC


Alot of energy is required to melt the oxide


It is therefore dissolved first in molten cryolite sodium hexafluoroaluminate IIINa3AlF6 to lower the melting point to about 800oC


The molten electrolyte is put in the Hall cell made up of a steel tank lined with carbon graphite and an anode suspended into the electrolyte


During the electrolysis


iAt the cathode


4Al3l  12e 4All


ii At the anode


6O2l 3O2g  12e


Aluminium is denser than the electrolyte therefore sink to the bottom of the Hall cell


At this temperature the Oxygen evolvedproduced at the anode reacts with carbon anode to form carbonIVoxide gas that escape to the atmosphere


Cs  O2g CO2g


The anode thus should be continuously replaced from time to time


Flow chart summary of extraction of aluminium from Bauxite


c Diagram showing the Hall cell  process for extraction of Bauxite


dUses of aluminium


i In making aeroplane parts buses tankers furniture because aluminium is very light


iiMaking duraluminan alloy which is harder and has a higher tensile strength


iiiMaking utensilssauce pansspoons because it is light and good conductor of electricity


ivMaking overhead electric cables because it is lightductile and good conductor of electricity


ivUsed in the thermite process for production of Manganese Chromium amd Titanium


e Environmental effects of extracting aluminium from Bauxite


CarbonIVoxide gas that escape to the atmosphere is a green house gas that causes global warming


Bauxite is extracted by open caste mining that causes soilenvironmental degradation


f Test for presence of Al3


If an ore is suspected to contain Al3 it is


iadded hot concentrated sulphuricVINitricVacid to free the ions present


iithe free ions are then added a precipitating reagent like 2M sodium hydroxide 2M aqueous ammonia


Practice


1An unknown rock X was discovered in Ukraine Test with dilute sulphuric VIacid shows rapid effervescence with production of a colourless gas A that forms a white precipitate with lime water and colourless solution B On adding 3cm3 of 2M sodium hydroxide a white precipitate C is formed that dissolves to form a colourless solution D on adding more sodium hydroxide On adding 2M aqueous ammonia a white precipitate E is formed which persist in excess aqueous ammoniaOn which on adding 5cm3 of 1M LeadIInitrateV to F a white precipitate G is formed which remains on heating


Identify


A HydrogenH2


B Aluminium sulphateVIAl2SO4 3


C Aluminium hydroxide AlOH4 3


D TetrahydroxoaluminateIII AlOH4 3


E Aluminium hydroxide AlOH 3


F Aluminium chloride AlCl3


2Aluminium is obtained from the ore with the formula Al2O3 2H2O The ore is first heated and refined to obtain pure aluminium oxide Al2O3 The oxide is then electrolysed to get Aluminium and oxygen gas using carbon anodes and carbon as cathode Give the common name of the ore from where aluminium is extracted from  mark


What would be the importance of heating the ore first before refining it1 mark


To remove the water of crystallization


The refined ore has to be dissolved in cryolite first before electrolysis Why is this necessary 1 mark


To lower the melting point of aluminium oxide from about 2015oC to 900oC so as to lower reduce cost of production


Why are the carbon anodes replaced every now and then in the cell for electrolysing aluminium oxide 1 mark


Oxygen produced at anode react with carbon to form carbonIVoxide gas that escape


State two uses of aluminium


In making aeroplane parts buses tankers utensils sauce pansspoons


Making overhead electric cables


Making duralumin


3 IRON


aNatural occurrence


Iron is the second most common naturally occurring metal It makes 4 of the earths crust as


bThe blast furnace for extraction of iron from Haematite and Magnetite


aRaw materials


ivCokecharcoal carbon


vLimestone


bChemical processes


Iron is usually extracted from Haematite Fe2O3 MagnetiteFe3O4 Siderite FeCO3These ores contain siliconIVoxideSiO2 and aluminiumIIIoxide Al2O3 as impurities


When extracted from siderite the ore must first be roasted in air to decompose the ironIICarbonate to IronIIoxide with production of carbonIVoxide gas


FeCO3s FeOs  CO2g


IronIIoxide is then rapidly oxidized by air to ironIIIoxideHaematite


4FeOs  O2g 2Fe2O3s


Haematite Fe2O3 MagnetiteFe3O4 coke and limestone are all then fed from top into a tall about 30metres in height tapered steel chamber lined with refractory bricks called a blast furnace


The furnace is covered with inverted double cap to preventreduce amount of any gases escaping


Near the basebottom blast of hot air at about 1000K 827oC is drivenforced into the furnace through small holes called Tuyeres


As the air enters it reacts with cokecharcoalcarbon to form carbonIVoxide gas This reaction is highly exothermic


Cs O2g CO2 g H  394kJ


This raises the temperature at the bottom of the furnace to about 2000K1650oCAs CarbonIVoxide gas rises up the furnace it reacts with more coke to form carbonIIoxide gasThis reaction is endothermic


CO2 g  Cs 2CO g H  173kJ


CarbonIIoxide gas is a strong reducing agent that reduces the ores at the upper parts of the furnace where temperatures are about 750K500oC ie


For Haematite


Fe2O3 s  3COg 2Fes  CO2g


For Magnetite


Fe3O4 s  4COg 3Fes  4CO2g


Iron is denser than iron ore As it falls to the hotter base of the furnace it melts and can easily be tapped off


Limestone fed into the furnace decomposes to quicklimecalcium oxide and produce more carbonIVoxide gas


CaCO3s CaOs  CO2g


Quicklimecalcium oxide reacts with the impurities siliconIVoxideSiO2 and aluminiumIIIoxideAl2O3in the ore to form calcium silicate and calcium aluminate


CaOs  SiO2s CaSiO3 l


CaOs  Al2O3s Ca Al2O4 l


Calcium silicate and calcium aluminate mixture is called slagSlag is denser than iron ore but less dense than iron therefore float on the pure iron It is tapped at different levels to be tapped off for use in


itarmacing roads


ii cement manufacture


iiias building construction material


cUses of Iron


Iron obtained from the blast furnace is hard and brittle It is called Pig iron It is remelted added scrap steel then cooled This iron is called cast iron


Iron is mainly used to make


igates pipes engine blocks rails charcoal iron boxeslamp posts because it is cheap


iinails cutlery scissors sinks vats spannerssteel rods and railway points from steel


Steel is an alloy of iron with carbon andor Vanadium Manganese Tungsten Nickel Chromium It does not rustcorrode like iron


e Environmental effects of extracting Iron from Blast furnace


iCarbonIVoxideCO2 gas is a green house gas that causesincreases global warming if allowed to escapeleak from the furnace


iiCarbonIIoxideCOgas is a highly poisonoustoxic odourless gas that can kill on leakage


It is preferentially absorbed by the haemoglobin in mammals instead of Oxygen to form a stable compound that reduce free hemoglobin in the blood


iii Haematite Fe2O3 MagnetiteFe3O4 and Siderite FeCO3 are extracted through quarrying open cast mining that cause soil  environmental degradation


f Test for the presence of Iron


Iron naturally exist in its compound as Fe2 Fe3


If an ore is suspected to contain Fe2 Fe3 it is


iadded hot concentrated sulphuricVINitricVacid to free the ions present


iithe free ions are then added a precipitating reagent like 2M sodium hydroxide 2M aqueous ammonia which forms


I an insoluble green precipitate in excess of 2M sodium hydroxide 2M aqueous ammonia if Fe2 ions are present


I an insoluble brown precipitate in excess of 2M sodium hydroxide 2M aqueous ammonia if Fe2 ions are present


4 COPPER


aNatural occurrence


Copper is found as uncombined elementmetal on the earths crust in Zambia Tanzania USA and Canada The chief ores of copper are


iCopper pyritesCuFeS2


bExtraction of copper from copper pyrites


Copper pyrites are first crushed into fine powder The powdered ore is the added water and oil The purpose of water is to dissolve hydrophilic substancesparticle The purpose of oil is to make cover copper ore particle so as to make it hydrophobic


Air is blown through the mixture Air creates bubbles that stick around hydrophobic copper ore The air bubbles raise through buoyancy small hydrophobic copper ore particles to the surface A concentrated ore floats at the top as froth This is called froth flotation The concentrated ore is then skimmed offThe ore is then roasted in air to form copperIsulphide sulphurIVoxide and iron II oxide


2CuFeS2s  4O2g Cu2Ss  3SO2g  2FeOs


Limestone CaCO3 and siliconIVoxide SiO2 are added and the mixture heated in absence of airSiliconIVoxide SiO2 reacts with iron II oxide to form Iron silicate which constitutes the slag and is removed


FeOs  SiO2s FeSiO3s


The slag separates off from the copperIsulphide CopperIsulphide is then heated in a regulated supply of air where some of it is converted to copper I oxide


2Cu2S s  3O2g 2Cu2Ss  2SO2g


The mixture then undergo self reduction in which copperIoxide is reduced by copperIsulphide to copper metal


Cu2S s  2Cu2O s 6Cu s  SO2g


The copper obtained has Iron sulphur and traces of silver and gold as impuritiesIt is therefore about 975 pure It is refined by electrolysiselectrolytic method


During the electrolysis of refining copper the impure copper is made the anode and a small pure strip is made the cathode


Electrode ionization takes place where


At the anode


Cus Cu2 aq  2e


Note Impure copper anode dissolveserodes into solution and decreases in size


At the Cathode


Cu2 aq  2e Cus


Note The copper ions in the electrolyteCuSO4 are reduced and deposited as copper metal at the cathode The copper obtained is 9998 pure


Valuable traces of silver and gold collect at the bottom of the electrolytic cell as sludge It is used to finance the extraction of copper pyrites


cFlow chart summary of extraction of copper from Copper pyrites


Electrolytic purification of impure copper


d Uses of copper


Copper is mainly used in


imaking low voltage electric cablescontact switches cockets and plugs because it is a good conductor of electricity


iiMaking solder because it is a good thermal conductor


iiiMaking useful alloys eg


Brass is an alloy of copper and ZincCuZn


Bronze is an alloy of copper and TinCuSn


German silver is an alloy of copper Zinc and NickelCuZnNi


ivMaking coins and ornaments


e Environmental effects of extracting copper from Copper pyrites


iSulphurIVoxide is a gas that has a pungent poisonous smell that causes head ache to human in high concentration


iiSulphurIVoxide gas if allowed to escape dissolves in water riversrain to form weak sulphuricIVacid lowering the pH of the water leading to marine pollution accelerated corrosionrusting of metalsroofs and breathing problems to human beings


iiiCopper is extracted by open caste mining leading to land environmental soil degradation


f Test for the presence of copper in an ore


Copper naturally exist in its compound as Cu2 Cu


Copper I  Cu is readily oxidized to copperII Cu2


If an ore is suspected to contain Cu2 Cu it is


iadded hot concentrated sulphuricVINitricVacid to free the ions present


iithe free ions are then added a precipitating reagent 2M sodium hydroxide 2M aqueous ammonia which forms


I an insoluble blue precipitate in excess of 2M sodium hydroxide if Cu2 ions are present


I an insoluble blue precipitate in 2M aqueous ammonia that dissolve to royaldeep blue solution in excess if Cu2 ions are present


gSample questions


Copper is extracted from copper pyrites as in the flow chart outlined below Study it and answer the questions that follow


5ZINC and LEAD


aNatural occurrence


Zinc occurs mainly as


iCalamineZinc carbonateZnCO3


iiZinc blendeZinc sulphideZnS


Lead occurs mainly as GalenaLeadIISulphide mixed with Zinc blende


bExtraction of ZincLead from Calamine Zinc blende and Galena


During extraction of Zinc  the ore is first roasted in air


For Calamine Zinc carbonate decompose to Zinc oxide and carbonIV oxide gas


ZnCO3s ZnOs  CO2g


Zinc blende does not decompose but reacts with air to form Zinc oxide and sulphurIV oxide gas


Galena as a useful impurity also reacts with air to form LeadII oxide and sulphurIV oxide gas


2ZnSs  3O2g 2ZnOs  2SO2g


Zinc blende


2PbSs  3O2g 2PbOs  2SO2g


Galena


The oxides are mixed with coke and limestoneIronIIoxide Aluminium III oxide and heated in a blast furnace


At the furnace temperatures limestone decomposes to quicklimeCaO and produce CarbonIVoxide gas


CaCO3s CaOs  CO2 g


CarbonIVoxide gas reacts with more coke to form the CarbonIIoxide gas


Cs  CO2 g 2CO g


Both CarbonIIoxide and carboncokecarbon are reducing agents


The oxides are reduced to the metals by either coke or carbon IIoxide


ZnOs  Cs Zng  CO g


PbOs  Cs Pbl  CO g


PbOs  COs Pbl  CO2 g


PbOs  COs Pbg  CO2 g


At the furnace temperature


iZinc is a gasvapour and is collected at the top of the furnace It is condensed in a spray of molten lead to prevent reoxidation to Zinc oxide On further cooling  Zinc collects on the surface from where it can be tapped off


iiLead is a liquid and is ale to trickle to the bottom of the furnace from where it is tapped off


QuicklimeCaO IronIIOxide AluminiumIIIoxide are used to remove silicasiliconIVoxide as silicates which float above Lead preventing its reoxidation back to LeadIIOxide


CaOs  SiO2s CaSiO3sl


SlagCalcium silicate


FeOs  SiO2s FeSiO3sl


SlagIron silicate


Al2O3s  SiO2s Al2SiO4sl


SlagAluminium silicate


cFlow chart on extraction of Zinc from Calamine Zinc blende


d Flow chart on extraction of Lead from Galena


e Uses of Lead


Lead is used in


imaking gunburettes


iimaking protective clothes against nuclear alpha raysparticle radiation in a nuclear reactor


iiiMixed with tinSn to make solder alloy


f Uses of Zinc


Zinc is used in


iGalvanizationwhen iron sheet is dipped in molten Zinc a thin layer of Zinc is formed on the surfaceSince Zinc is more reactive than iron it reacts with elements of airCO2 O2  H2O to form basic Zinc carbonateZnCO3ZnOH2This sacrificial method protects iron from corrosionrusting


iiAs negative terminal and casing in dryLaclanche cells


iiiMaking brass alloy with copperCuZn


g Environmental effects of extracting Zinc and Lead


i Lead and Lead salts are carcinogeniccauses cancer


iiCarbonIVoxide is a green house gas that causesaccelerate global warming


iiiCarbonIIoxide is a colourless odourless poisonous toxic gas that combines with haemoglobin in the blood to form stable carboxyhaemoglobin reducing free haemoglobin leading to death


iv SulphurIVoxide is a gas that has a pungent poisonous smell that causes headache to human if in high concentration


vAny leakages in SulphurIVoxide gas escapes to the water bodies to form weak sulphuricVIacid lowering the pH of the water This causes marine pollution death of aquatic life accelerated rustingcorrosion of metalsroofs and breathing problems to human beings


h Test for presence of Zinc Lead


If an ore is suspected to contain ZincLead it is


Iadded hot concentrated NitricVacid to free the ions present


Note


Concentrated SulphuricVIacid forms insoluble PbSO4 thus cannot be used to free the ions in Lead salts


IIthe free ions are then added a precipitating reagent mostly 2M sodium hydroxide or 2M aqueous ammonia with the formation of


ia soluble precipitate in excess of 2M sodium hydroxide if Zn2 Pb2 Al3ions are present


iia white precipitate that dissolves to form a colorless solution in excess 2M aqueous ammonia if Zn2ions are present


iiian insoluble white precipitate in excess 2M aqueous ammonia if Pb2 Al3ions are present


iv Pb2 ions form a white precipitate when any soluble SO42 SO32 CO32 Cl is added while Al3 ions do not form a white precipitate


v Pb2 ions form a yellow precipitate when any soluble Ieg Potassiumsodium Iodide is added while Al3 ions do not form a yellow precipitate


vi Pb2 ions form a black precipitate when any soluble Seg Potassiumsodium sulphide is added while Al3 ions do not form a black precipitateie


6GENERAL SUMMARY OF METALS


a Summary methods of extracting metal from their ore


The main criteria used in extraction of metals is based on its position in the electrochemicalreactivity series and its occurrence on the earths crust


b Summary of extraction of common metal


of metal


d Physical properties of metal


Metals form giant metallic structure joined by metallic bond from electrostatic attraction between the metallic cation and free delocalized electrons


This makes metals to have the following physical properties


iHigh melting and boiling points


The giant metallic structure has a very close packed metallic lattice joined by strong electrostatic attraction between the metallic cation and free delocalized electronsThe more delocalized electrons the higher the meltingboiling points eg


Aluminium has a melting point of about 2015oC while that of sodium is about 98oCThis is mainly because aluminium has morethree delocalized electrons than sodiumhas one


Aluminium has a boiling point of about 2470oC while that of sodium is about 890oCThis is mainly because aluminium has morethree delocalized electrons than sodiumhas one


iiHigh thermal and electrical conductivity


All metals are good thermal and electrical conductors as liquid or solids The more delocalized electrons the higher the thermal and electrical conductivity eg


Aluminium has an electrical conductivity of about 382 x 199 ohms per metre Sodium has an electrical conductivity of about 218 x 199 ohms per metre


iiiShinyLustrous


The free delocalized electrons on the surface of the metal absorb vibrate and then scatterreemitlose light energy All metals are therefore usually shades of grey in colour except copper which is shiny browneg


Zinc is bluish grey while iron is silvery grey


ivHigh tensile strength


The free delocalized electrons on the surface of the metal atoms binds the surface immediately when the metal is coiledfolded preventing it from breaking being brittle


vMalleable


Metals can be made into thin sheet The metallic crystal lattice on being beatenpressedhammered on two sides extend its length and widthbredth and is then immediately bound by the delocalized electrons preventing it from breakingbeing brittle


viDuctile


Metals can be made into thin wires The metallic crystal lattice on being beatenpressedhammered on all sides extend its length is then immediately bound by the delocalized electrons preventing it from breakingbeing brittle


Revision questions


1Given some soil  dilute sulphuricVIacidmortarpestlefilter paperfilter funnel and 2M aqueous ammoniadescribe with explanationhow you would show that the soil contain Zinc


Place the soil sample in the pestle Crush using the mortar to reduce the particle sizeincrease its surface area


Add dilute sulphuricVIacid to free the ions in soil sample


Filter to separate insoluble residue from soluble filtrate


To filtrateadd three drops of aqueous ammonia as precipitating reagent A white precipitate of ZnOH2 PbOH2 or AlOH3 is formed


Add excess aqueous ammonia to the white precipitate If it dissolves the Zn2 ions are present ZnOH2 react with excess ammonia to form soluble ZnOH42 complex


2In the extraction of aluminiumthe oxide is dissolved in cryolite


iWhat is the chemical name of cryolite


Sodium hexafloroaluminateNa3AlF6


iiWhat is the purpose of cryolite


To lower the melting point of the electrolyteAluminium oxide from about 2015oC to 900oC


iiiName the substance used for similar purpose in the Down cell


Calcium chlorideCaCl2


ivAn alloy of sodium and potassium is used as coolant in nuclear reactorsExplain


Nuclear reactors generate a lot of heat energy sodium and potassium alloy reducelower the high temperature in the reactors


vAluminium metal is used to make cooking utensils in preference to other metalsExplain


Aluminium


i is a very good conductor of electricity because it has three delocalized electrons in its metallic structure


iiis cheapmalleableductile and has high tensile strength


iiion exposure to fireheat form an impervious layer that prevent it from rapid corrosion


3Study the scheme below and use it to answer the questions that follow


aIdentify


isolid residue L


iiSolid N


Aluminium hydroxide AlOH3


iiiFiltrate M


Sodium tetrahydroxoaluminate NaAlOH4 and sodium silicate NaSiO3


ivSolid P


Aluminium oxide Al2O3


vGas Q


viProcess K1


Filtration


viiProcess K2


Electrolysis


bWrite the equation for the reaction taking place in the formation of solid P from solid N


2AlOH3  Al2O3 s  3H2Ol


cName a substance added to solid N before process Process K2 take place


CryoliteSodium tetrahydroxoaluminate NaAlOH4


dState the effect of evolution of gas Q on


iprocess K2


Oxygen produced at the anode reacts with the carbon anode to form carbonIV oxide which escape The electrolytic process needs continuous replacement of the carbon anode


iithe environment


Oxygen produced at the anode reacts with the carbon anode to form carbonIV oxide which escape to the atmosphereCO2 is a green house gas that cause global warming


eAn aluminium manufacturing factory runs for 24 hours If the total mass of aluminium produced is 27000kg


iCalculate the current used Faraday constant96500Coulombs Al270


iiassuming all the gas produced react with 200kg of anode calculate the loss in mass of the electrodeMolar gas volume at room temperature  24dm3C120


Working


Equation at Cathode Al3l  3e  All


27g Al  3 Faradays  3 x 96500C


27000kg x 1000 g  27000kg x 1000 g x 3 x 96500C 27g


289500000000 Coulombs


Current  Quantity of electricity 289500000000 Coulombs Time in seconds 24 x 60 x 60


Equation at Anode 2O2l  4e  O2g


4 Faradays  4 x 96500C24dm3 O2g


289500000000 Coulombs  289500000000 Coulombs x 24dm3 4 x 96500C


Chemical equation at anode


O2g  C s  CO2g


Method 1


24dm3 of O2g  120g Carbon


18000000dm3 of O2g  18000000dm3 x 12  9000000g  9000kg 24dm3 1000g


Loss in mass of the carbon graphite anode  9000kg


NBMass of the carbon graphite anode remaining 27000kg  9000kg 18000kg


The flow chart below shows the extraction of iron metalUse it to answer the questions that follow


aIdentify


igas P


iiSolid Q


Carboncokecharcoal


iiiSolid R


ivSolid V


Limestonecalcium carbonateCaCO3


vSolid S


IronFe


bWrite the chemical equation for the reaction for the formation of


iSolid S


Fe2O3s  3COg  2Fes  3CO2g


iiCarbonIIoxide


Cs  CO2 g  2CO g


iiiSlag


SiO2s  CaOs  CaSiO3s


Al2O3 s  CaOs  Ca Al2O4s


ivGas P


Cs  O2 g  CO2 g


cState two uses of


Iron is used in making


igates pipes engine blocks rails charcoal iron boxes lamp posts because it is cheap


iinails cutlery scissors sinks vats spanners steel rods and railway points from steel


Steel is an alloy of iron with carbon andor Vanadium Manganese Tungsten Nickel Chromium


It does not rustcorrode like iron


iiSlag


i tarmacing roads


ii cement manufacture


iii as building construction material


3You are provided with sulphuricVIacid 2M aqueous ammonia and two ores suspected to contain copper and iron Describe with explanation how you would differentiate the two ores


Crush the two ores separately in using a mortar and pestle to reduce the particle sizeincrease the surface area


Add sulphuricVIacid to separate portion of the ore Filter


To a portion of the filtrateadd three drops of 2M aqueous ammonia then axcess


Results


A green precipitate insoluble in excess 2M aqueous ammonia confirms the ore contain Fe2 ion


A brown precipitate insoluble in excess 2M aqueous ammonia confirms the ore contain Fe3 ion


A blue precipitate that dissolve in excess 2M aqueous ammonia to form a deeproyal blue solution confirms the ore contain Cu2 ion


4 Use the flow chart below showing the extraction of Zinc metal to answer the questions that follow


aName


itwo ores from which Zinc can be extracted


Zinc blendeZnS


iitwo possible identity of gas P


SulphurIVoxideSO2 from roasting Zinc blende


CarbonIVoxideCO2 from decomposition of Calamine


bWrite a possible chemical equation taking place in the roasting chamber


2ZnSs  3O2 g  2ZnOs  2SO2g


ZnCO3s  ZnOs  CO2g


cExplain the effect of the byproduct of the roating on the environment


Sulphur IVoxide from roasting Zinc blende is an acidic gas that causes acid rain on dissolving in rain water


CarbonIVoxideCO2 from decomposition of Calamine is a green house gas that causes global warming


diName a suitable reducing agent used in the furnace during extraction of Zinc


CarbonIIoxide


iiWrite a chemical equation for the reduction process


ZnOs  COg  Zns  CO2g


eiBefore electrolysis the products from roasting is added dilute sulphuric VIacid Write the equation for the reaction with dilute sulphuricVIacid


ZnOs  H2SO4 aq  Zn SO4aq  H2g


iiDuring the electrolysis for extraction of Zincstate the


I Anode used


Aluminium sheet


II Cathode used


Lead plate coated with silver


iiWrite the equation for the electrolysis for extraction of Zinc at the


ICathode


Zn2aq  2e  Zns


IIAnode


4OHaq  2H2Ol  O2s  4e


fiWhat is galvanization


Dipping Iron in molten Zinc to form a thin layer of Zinc to prevent iron from rusting


iiGalvanized iron sheet rust after some time Explain


The thin layer of Zinc protect Iron from rusting through sacrificial protection When all the Zinc has reacted with elements of air Iron start rusting


gState two uses of Zinc other than galvanization


Making brassZinccopper alloy


Making german silverZinccoppernickel alloy


As casing for dry cellsbattery


hCalculate the mass of Zinc that is produced from the reduction chamber if 6400kg of Calamine ore is fed into the roaster Assume the process is 80 efficient in each stageZn640C120O160


Molar mass ZnCO3s 124g


Molar mass Zn  64g


Molar mass ZnO  80g


Chemical equation


ZnCO3s  ZnOs  CO2g


Method 1


124g ZnCO3  80g ZnO


6400kg x1000g ZnCO3  6400 x1000 x 80  512000000 g of ZnO


100  512000000 g of ZnO


80  80 x 512000000 g  409600000g of ZnO


ZnOs  COg  Zns  CO2g


80g ZnOs  64g Zns


409600000g of ZnO  409600000g x 64  327680000 g Zn


100  327680000 g Zn


80  80 x 327680000 g Zn  262144000g of Zn


Mass of Zinc produced  262144000g of Zn


5An ore is suspected to bauxite Describe the process that can be used to confirm the presence of aluminium in the ore


Crush the ore to fine powder to increase surface areareduce particle size


Add hot concentrated sulphuricVInitricV acid to free the ions


Filter Retain the filtrate


Add excess aqueous ammonia to a sample of filtrate


A white precipitate confirms presence of either Al3 or Pb2


Add sodium sulphatedilute sulphuricVIto another portion of filtrate


No white precipitate confirms presence of Al3


Or Add potassium iodide to another portion of filtrate


No yellow precipitate confirms presence of Al3


6The flow chart below illustrate the industrial extraction of Lead metal


aiName the chief ore that is commonly used in this process


GalenaPbS


iiExplain what take place in the roasting furnace


ELECTROCHEMISTRY


Electrochemistry can be defined as the study of the effects of electricity on a substance compound and how chemical reactions produce electricity Electrochemistry therefore deals mainly with


Reduction and oxidation


Electrochemical voltaic cell


Electrolysis electrolytic cell


iREDUCTION AND OXIDATION REDOX


1 In teams of oxygen transfer


i Reduction is removal of oxygen


ii Oxidation is addition of oxygen


iii Redox is simultaneous addition and removal of oxygen


iv Reducing agent is the species that undergoes oxidation therefore gains oxygen


v Oxidizing agent is the species that undergoes reduction therefore loosesdonates oxygen


eg When hydrogen is passed through heated copper II oxide it is oxidised to copper metal as in the equation below


CuO s  H2 g  Cu s  H2O l


Oxidising agent Reducing agent


2 In terms of hydrogen transfer


i Oxidation is the removal of hydrogen


ii Reduction is the addition of hydrogen


iii Redox is simultaneous addition and removal of hydrogen


iv Reducing agent is the species that undergoes oxidation therefore looses donates hydrogen


v Oxidizing agent is the species that undergoes reduction therefore gains hydrogen


eg When hydrogen sulphide gas is bubbled into a gas jar containing chlorine gas it is oxidized loose the hydrogen to sulphur yellow solid The chlorine is reduced gain hydrogen to hydrogen chlorine gas


Cl2 g  H2S g  SS  2HCl g


Oxidizing agent Reducing agent


3 In terms of electron transfer


i Oxidation is donation loss removal of electrons


ii Reduction is gain accept addition of electrons


iii Redox is simultaneous gain accept addition and donation loss removal of electrons


iv Reducing agent is the species that undergoes oxidation therefore looses donates electrons


v Oxidizing agent is the species that undergoes reduction therefore gains accepts electrons


Example


Displacement of metals from their solutions


Place 5cm3 each of Iron II sulphate VI solution into three different test tubes Add about 1g of copper tunings  powder into one test tube then zinc and magnesium powders separately into the other test tubes Shake thoroughly for 2 minutes each Record any colour changes in the table below


Explanation


When a more reactive metal is added to a solution of less reactive metal it displaces it from its solution


When a less reactive metal is added to a solution of a more reactive metal it does not displace it from its solution


Copper is less reactive than iron therefore cannot displace iron its solution


Zinc is more reactive than iron therefore can displace iron from its solution


Magnesium is more reactive than iron therefore can displace iron from its solution


In terms of electron transfer


the more reactive metal undergoes oxidation reducing agent by donatingloosing electrons to form ions


the less reactive metal undergoes reduction oxidizing agent by its ions in solution gaining acceptingacquiring the electrons to form the metal


displacement of metals involves therefore electron transfer from a more reactive metal to ions of another less reactive metal


Examples


Zns  Zn2aq  2e oxidationdonation of electrons


Fe2aq  2e  Fes reductiongain of electrons


Fe2aq  Zns  Zn2aq  Fes redoxboth donation and gain of electrons


Mgs  Mg2aq  2e oxidationdonation of electrons


Fe2aq  Mgs  Mg2aq  Fes redoxboth donation and gain of electrons


Cu2aq  2e  Cus reductiongain of electrons


Cu2aq  Zns  Zn2aq  Cus redoxboth donation and gain of electrons


Fes  Fe2aq  2e oxidationdonation of electrons


2Agaq  2e  2Ags reductiongain of electrons


2Agaq  Fes  Fe2aq  2Ags redoxboth donation and gain of electrons


Cl2g  2e  2Claq reductiongain of electrons


Cl2g  Zns  Zn2aq  2Claq redoxboth donation and gain of electrons


2Mgs  2Mg2aq  4e oxidationdonation of electrons


O2g  4e  2O2aq reductiongain of electrons


O2g  2Mgs  2Mg2aq  2O2aq redoxboth donation and gain of electrons


Note


iThe number of electrons donatedlost MUST be equal to the number of electrons gainedacquired


iDuring displacement reaction the colour of ions salts fades but does not if displacement does not take place eg


aGreen colour of Fe2aq fades if Fe2aq ions are displaced from their solution Green colour of Fe2aq appear if Feiron displaces another saltions from their solution


bBlue colour of Cu2aq fades if Cu2aq ions are displaced from their solution and brown copper deposits appear Blue colour of Cu2aq appear if Cucopper displaces another saltions from their solution


cBrown colour of Fe3aq fades if Fe3aq ions are displaced from their solution Brown colour of Fe3aq appear if Feiron displaces another saltions from their solution to form Fe3aq


iiiDisplacement reactions also produce energyheat The closernearer the metals in the reactivityelectrochemical series the less energyheat of displacement


ivThe higher the metal in the reactivity series therefore the easier to loosedonate electrons and thus the stronger the reducing agent


4 aIn terms of oxidation number


i Oxidation is increase in oxidation numbers


ii Reduction is decrease in oxidation numbers


iii Redox is simultaneous increase in oxidation numbers of one speciessubstance and a decrease in oxidation numbers of another speciessubstance


iv Reducing agent is the species that undergoes oxidation therefore increases its oxidation number


v Oxidizing agent is the species that undergoes reduction therefore increases its oxidation number


bThe ideaconcept of oxidation numbers usesapplies the following simple guideline rules


Guidelines rules applied in assigning oxidation number


1Oxidation number of combined Oxygen is always 2 except in peroxides Na2O2H2O2 where its Oxidation number is 1


2Oxidation number of combined Hydrogen is always 1except in Hydrides NaHKH where its Oxidation number is 1


3All atoms and molecules of elements have oxidation number 0 zero


4All combined metals and nonmetals have oxidation numbers equal to their valency oxidation state eg


5Sum of oxidation numbers of atoms of elements making a compound is equal zero0 eg


Using this rule an unknown oxidation number of an atom in a compound can be determined as below


a CuSO4 has


one atom of Cu with oxidation number 2 refer to Rule 4


one atom of S with oxidation number 6  refer to Rule 4


six atoms of O each with oxidation number 2 refer to Rule 4


Sum of oxidation numbers of atoms in CuSO4  2  6  2 x 6  0


b H2SO4 has


two atom of H each with oxidation number 1 refer to Rule 2


four atoms of O each with oxidation number 2 refer to Rule 4


Sum of oxidation numbers of atoms in H2SO4  2  6  2 x 4  0


c KMnO4 has


one atom of K with oxidation number 1 refer to Rule 4


one atom of Mn with oxidation number 7  refer to Rule 4


Sum of oxidation numbers of atoms in KMnO4  1  7  2 x 4  0


Determine the oxidation number of


INitrogen in


NO  x  2  0 thus x  0  2   2


The chemical name of this compound is thus NitrogenIIoxide


NO2  x  2 x2 0 thus x  0  4   4


The chemical name of this compound is thus NitrogenIVoxide


N2O  2x  2  0 thus 2x  0  2  22 1


The chemical name of this compound is thus NitrogenIoxide


II Sulphur in


SO2  x  2 x2 0 thus x  0  4   4


The chemical name of this compound is thus SulphurIVoxide


SO3  x  2 x3 0 thus x  0  6   6


The chemical name of this compound is thus SulphurVIoxide


H2SO4  1 x 2  x  2 x 4 thus x 0 2 8 6


The chemical name of this compound is thus SulphuricVIacid


H2SO3  1 x 2  x  2 x 3 thus x 0 2 6 4


The chemical name of this compound is thus SulphuricIVacid


III Carbon in


CO2  x  2 x2 0 thus x  0  4   4


The chemical name of this compound is thus carbonIVoxide


CO  x  2  0 thus x  0  2   2


The chemical name of this compound is thus carbonIIoxide


H2CO3  1 x 2  x  2 x 3 thus x 0 2 6 4


The chemical name of this compound is thus CarbonicIVacid


IVManganese in


MnO2  x  2 x2 0 thus x  0  4   4


The chemical name of this compound is thus ManganeseIVoxide


KMnO4  1  x  2 x 4 thus x 0 1 8 7


The chemical name of this compound is thus Potassium manganateVII


VChromium in


Cr2O3  2x  2 x 3 0 thus 2x  0  6  6  2 3


The chemical name of this compound is thus ChromiumIIIoxide


K2Cr2O7  1 x 2  2x  2 x7 0


thus 2x  0  2 14  12  2 6


The chemical name of this compound is thus Potassium dichromateVI


K2CrO4  1 x 2  x  2 x4 0


thus 2x  0  2 8  12  2 6


The chemical name of this compound is thus Potassium chromateVI


6The sum of the oxidation numbers of atoms of elements making a charged radicalcomplex ion is equal to its charge