Air from the atmosphere is passes through electrostatic precipitatorsfilters to remove unwanted gases like Nitrogen Carbon IV oxide dust smoke which may poison the catalyst The ammonia air mixture is compressed to 9 atmospheres to reduce the distance between reacting gases


The mixture is passed through the heat exchangers where a temperature of 850oC900oC is maintained


The first reaction takes place in the catalytic chamber where Ammonia reacts with the air to form Nitrogen II Oxide and water


Optimum condition in Ostwalds process


Chemical equation


4NH3 g  5O2 g  PtRh  4NO g  6H2O g H  950kJ


The reaction is reversible and exists in dynamic equilibrium where the products reform back the reactants The following factors are used to increase the yieldamount of Nitrogen II oxide


iRemoving Nitrogen II oxide gas once formed shift the equilibrium forward to the right to replace the Nitrogen II oxide


Morehigher yield of Nitrogen II oxide is attained as reactants try to return the equilibrium balance


iiIncrease in pressure shift the equilibrium backward to the left where there are less volumemolecules


Lesslower yield of Nitrogen II oxide is attained


Very low pressures increases the distance between reacting NH3 and O2 molecules


An optimum pressure of about 9 atmospheres is normally used


Cooling the mixture condenses the water vapour to liquid water


iiiIncrease in temperature shift the equilibrium backward to the left because the reaction is exothermic H  950kJ


Nitrogen II oxide and water vapour formed decomposes back to Ammonia and Oxygen to remove excess heat therefore a less yield of Nitrogen II oxide is attained


Very low temperature decreases the collision frequency of Ammonia and Oxygen and thus the rate of reaction too slow and uneconomical


An optimum temperature of about 900oC is normally used


ivPlatinum can be used as catalyst


Platinum is very expensive It is


promoted with Rhodium to increase the surface areaarea of contact


addedcoated on the surface of asbestos to form Platonized asbestos to reduce the amountquantity used


The catalyst does not increase the yield of Nitrogen II Oxide but it speed up its rate of formation


Nitrogen II oxide formed is passed through an oxidation reaction chamber where more air oxidizes the Nitrogen II Oxide to Nitrogen IV Oxide gas


Chemical equation


2NO g  O2 g  2NO2 g


Nitrogen IV Oxide gas is passed up to meet a downward flow of water in the absorption chamber The gas reacts with water to form a mixture of Nitric V and Nitric III acids


2NO2 g  H2O l  HNO2 as  HNO3 as


Excess air is bubbled through the mixture to oxidize Nitric III HNO2 as to Nitric VHNO3 as


O2 g  2HNO2 as  2HNO3 as


Overall chemical equation in the absorption chamber


O2 g  4NO2 g  2H2O l  4HNO3 as


The acid is 65 concentrated It is made 100 concentrated by either


i fractional distillation or


ii added to concentrated sulphuric VI acid to remove the 35 of water


A factory uses 630 kg of 68 pure nitric V acid per day to produce an ammonium fertilizer for an agricultural county If the density of the acid is 142 gcm3 calculate


i the concentration of the acid used in moles per litre


Molar mass HNO3  63


Method 1


Moles of HNO3 in 1cm3  Mass in 1cm3 142  142  00225 moles


Molar mass HNO3 63


Molarity  Moles x 100000225 moles x10000  225molesdm3M


1 cm3


100  225molesdm3M


68  68 x 225  153M molesdm3


Method 2


Moles of HNO3 in 1000cm3  Mass in 1000cm3 142 x1000


225397 molesdm3M


100  225397 molesdm3M


68  68 x 225397  15327 molesdm3


ii the volume of ammonia gas at rtp used H10 N140 O160 one mole of gas  24 dm3 at rtp


Chemical equation


HNO3 as  NH3 g  NH4NO3 as


Mole ratio HNO3 as NH3 g  1 1


1 mole HNO3 as  24dm3 NH3 g


15327 mole HNO3 as 15327 mole x 24 dm3  367848dm3


iii the number of crops which can be applied the fertilizer if each crop requires 40g


HNO3 aq  NH3 g  NH4NO3 aq


Molar mass NH4NO3 80 g


Mole ratio HNO3 NH4NO3  1 1


Mass of HNO3 in 630 kg  68 x 63 4284kg


1 mole HNO3 aq 63g  80g NH4NO3


4284x1000 g HNO3 aq  4284x1000 g x 80


Mass of fertilizer  54400g  13600 crops


Mass per crop 40


E NITRATE V NO3 and NITRATE III NO2 Salts


Nitrate V NO3 and Nitrate III NO2 are salts derived from Nitric VHNO3 and Nitric IIIHNO2 acids Both HNO3 and HNO2 are monobasic acids with only one ignitable hydrogen in a molecule


Only KNO2 NaNO2 and NH4NO2 exist All metallic nitrate V salts exist


All Nitrate V NO3 and Nitrate III NO2 are solubledissolve in water


aEffect of heat on Nitrate V NO3 and Nitrate III NO2 salts Test for presence of Nitrate V NO3 ions in solid state


1 All Nitrate III NO2 salts are not affected by gentle or strong heating except ammonium nitrate III NH4NO2


Ammonium nitrate III NH4NO2 is a colourless solid that decompose to form Nitrogen gas and water


Chemical equation


NH4NO2 s  H2O l  N2 g


This reaction is used to prepare small amounts of Nitrogen in a school laboratory


2 All Nitrate V NO3 salts decompose on strong heating


Experiment


Put  spatula full of sodium nitrate V into a test tube Place moist bluered litmus papers on the mouth of the test tube Heat strongly when test tube is slanted


Test the gases produced using glowing splint


Caution i Wear safety gas mask and hand gloves


iiLead II nitrate V decomposes to Lead II oxide that reacts and fuses with the test tube permanently


Repeat with potassium nitrateV copperII nitrateV LeadIInitrateV silver nitrateV Zinc nitrateV Magnesium nitrateV and Ammonium nitrateV


Observations


Cracking sound


Brown fumesgas produced except in potassium nitrate V and Sodium nitrate V


Glowing splint relightsrekindles but feebly in Ammonium nitrateV


Black solid residue with copperII nitrateV


White residuesolid with sodium nitrateV potassium nitrateVsilver nitrateV Magnesium nitrateV


Yellow residuesolid when hot but white on cooling with Zinc nitrateV


Brown residuesolid when hot but yellow on cooling with LeadIInitrateV


Explanation


1 Potassium nitrateV and Sodium nitrateV decomposes on strong heating to form potassium nitrateIII and Sodium nitrateIII producing Oxygen gas Oxygen gas relightsrekindles a glowing splint


Chemical equation


2KNO3s  2KNO2s  O2 g


2NaNO3s  2NaNO2s  O2 g


2Heavy metal nitrateVsalts decomposes to form the oxide brown nitrogen IV oxide and Oxygen gas


CopperIIoxide is blackZinc oxide is yellow when hot and white when coolcold LeadIIoxide is yellow when coldcool and brown when hotheated


Hydrated copperIInitrate is blue On heating it melts and dissolves in its water of crystallization to form a green solution When all the water of crystallization has evaporatedthe nitrateVsalt decomposes to black CopperIIoxide and a mixture of brown nitrogenIVoxide gas and colourless Oxygen gas


2CuNO32s  2CuO s  4NO2g  O2s


2CaNO32s  2CaO s  4NO2g  O2s


2ZnNO32s  2ZnO s  4NO2g  O2s


2MgNO32s  2MgO s  4NO2g  O2s


2PbNO32s  2PbO s  4NO2g  O2s


2FeNO32s  2FeO s  4NO2g  O2s


Silver nitrateVand MercuryIInitrate decomposes to the corresponding metal and a mixture of brown nitrogenIVoxide gas and colourless Oxygen gas


2AgNO3 s  2Ag s  2NO2g  O2s


HgNO32s  Hgl  2NO2g  O2s


The productionevolution of brown fumes of NitrogenIVoxide gas on heating a salt is a confirmatory test for presence of NO3 ions of heavy metals


bBrown ring test Test for presence of NitrateV NO3 ions in aqueous solution state


Experiment


Place 5cm3 of Potassium nitrateVsolution onto a clean test tube Add 8 drops of freshly prepared IronIIsulphateVIsolution Swirl shake


Using a test tube holder to firmly slant and hold the test tube carefully add 5cm3 of Concentrated sulphuric VI acid down along the side of test tubeDo not shake the test tube contents


Caution Concentrated sulphuric VI acid is highly corrosive


Observation


Both Potassium nitrateVand freshly prepared IronIIsulphate VIdo not form layers


On adding Concentrated SulphuricVIacidtwo layers are formed


A brown ring is formed between the layers


Explanation


All nitrateVsalts are soluble They form a miscible mixture when added freshly prepared IronIIsulphateVIsolution Concentrated sulphuricVIacid is denser than the miscible mixture thus settle at the bottom


At the junction of the layers the acid reacts with nitrateVsalts to form NitricVacidHNO3 NitricVacidHNO3 is reduced to Nitrogen IIoxide by the IronIIsulphateVI salt to form the complex compound NitrosoironIIsulphateVIFeSO4NO  NitrosoironIIsulphateVI is brown in colourIt forms a thin layer at the junction between concentrated sulphuric VIacid and the miscible mixture of freshly prepared IronII sulphateVI and the nitrateVsalts as a brown ring


Chemical equation


FeSO4aq  NOg  FeSO4NOaq


NitrosoironIIsulphateVIcomplex


The brown ring disappear if shaken because concentrated sulphuric VIacid mixes with the aqueous solution generating a lot of heat which decomposes NitrosoironIIsulphateVIFeSO4NO to ironIIsulphateVI and NitrogenIIoxide


FeSO4NOaq FeSO4aq  NOg


IronIIsulphateVI solution is easilyreadily oxidized to ironIIIsulphateVI on exposure to airoxygen The brown ring test thus require freshly prepared IronII sulphateVI solution


cDevardas alloy test Test for presence of NitrateV NO3 ions in aqueous solution state


Experiment


Place 5cm3 of Potassium nitrateVsolution onto a clean test tube Add 5 drops of sodium hydroxide solution Swirl shake Add a piece of aluminium foil to the mixtureHeatTest any gases produced using both blue and red litmus papers


Observation Inference


Effervescencebubblesfizzing


colourless gas that has a pungent smell of urine NO3


Blue limus paper remain blue


Red litmus paper turn red


Explanation


The Devardas alloy test for NO3 ions in solution was developed by the Italian scientist Artulo Devarda18591944


When a NO3salt is added sodium hydroxide and aluminium foil effervescence of ammonia gas is a confirmatory test for NO3 ions


CHEMISTRY OF SULPHUR


ASULPHUR S


Sulphur is an element in Group VI Group 16of the Periodic table  It has atomic number 16 and electronic configuration 16 and valency 2 divalent and thus forms the ion S2


A Occurrence


Sulphur mainly occurs


i as free element in Texas and Louisiana in USA and Sicily in Italy


iiHydrogen sulphide gas in active volcanic areas eg Olkaria near Naivasha in Kenya


iiias copper pyritesCuFeS2 Galena PbSZinc blendeZnSand iron pyritesFeS2 in other parts of the world


B Extraction of Sulphur from Fraschs process


Suphur occurs about 200 metres underground The soil structure in these areas is usually weak and can easily cave in


Digging of tunnels is thus discouraged in trying to extract the mineral


Sulphur is extracted by drilling three concentric round pipes of diameter of ratios 28 18 centimeters


Superheated water at 170oC and 10atmosphere pressure is forced through the outermost pipe


The high pressures ensure the water remains as liquid at high temperatures instead of vapour of vapour gas


The superheated water melts the sulphur because the melting point of sulphur is lower at about at about 115oC


A compressed air at 15 atmospheres is forced pumped through the innermost pipe


The hot air forces the molten sulphur up the middle pipe where it is collected and solidifies in a large tank


It is about 99 pure


Diagram showing extraction of Sulphur from Fraschs Process


C Allotropes of Sulphur


1 Sulphur exists as two crystalline allotropic forms


iRhombic sulphur


iiMonoclinic sulphur


Rhombic sulphur and Monoclinic sulphur have a transition temperature of 96oCThis is the temperature at which one allotrope changes to the other


2 Sulphur exists in noncrystalline forms as


iPlastic sulphur


Plastic sulphur is prepared from heating powdered sulphur to boil then pouring a thin continuous stream in a beaker with cold water A long thin elastic yellow thread of plastic sulphur is formed If left for long it turn to bright yellow crystalline rhombic sulphur


iiColloidal sulphur


Colloidal sulphur is formed when sodium thiosulphate Na2S2O3 is added hydrochloric acid to form a yellow precipitate


D Heating Sulphur


A molecule of sulphur exists as puckered ring of eight atoms joined by covalent bonds as S8


On heating the yellow sulphur powder melts at 113oC to clear amber liquid with low viscosity and thus flows easily


On further heating to 160oC the molten liquid darkens to a brown very viscous liquid that does not flow easily


This is because the S8 rings break into S8 chain that join together to form very long chains made of over 100000 atoms of Sulphur


The long chains entangle each other reducing their mobility flow and hence increases their viscosity


On continued further heating to above 160oC the viscous liquid darkens but becomes more mobileflows easily and thus less viscous


This is because the long chains break to smallershorter chains


At 444oC the liquid boils and forms brown vapour of a mixture of S8 S6 S2 molecules that solidifies to S8 ring of flowers of sulphur on the cooler parts


Summary of changes on heating sulphur


E Physical and Chemical properties of SulphurQuestions


1 State three physical properties unique to Sulphur


Sulphur is a yellow solid insoluble in water soluble in carbon disulphidetetrachloromethanebenzene poor conductor of heat and electricity It has a melting point of 115oC and a boiling point of 444oC


2 Moistdampwet blue and red litmus papers were put in a gas jar containing airoxygen Burning sulphur was then lowered into the gas jar State and explain the observation made


Observations


Sulphur melts then burns with a blue flame


Colourless gas produced that has a pungent smell


Red litmus paper remains red Blue litmus paper turns red


Explanation


Sulphur burns in air and faster in Oxygen to form SulphurIVOxide gas and tracessmall amount of SulphurVIOxide gas Both oxides react with water to form the corresponding acidic solution ie


i SulphurIVOxide gas reacts with water to form sulphuricIVacid


ii SulphurVIOxide gas reacts with water to form sulphuricVIacid


Chemical equation


Ss  O2g  SO2g SulphurIVOxide gas


2Ss  3O2g  2SO3g SulphurVIOxide gas traces


SO2g  H2Ol  H2 SO3 aq  sulphuricIVacid SO3g  H2Ol  H2 SO4 aq  sulphuricVIacid


3 Iron filings were put in a test tube containing powdered sulphur then heated on a Bunsen flame Stop heating when reaction starts State and explain the observations made Test the effects of a magnet on the mixture before and after heating Explain


Before heating the magnet attracts iron filings leaving sulphur


After heating the magnet does not attract the mixture


After heating a red glow is observed that continues even when heating is stopped


Black solid is formed


Explanation Iron is attracted to a magnet because it is ferromagnetic


When a mixture of iron and sulphur is heated the reaction is exothermic giving out heat energy that makes the mixture to continue glowing even after stopping heating


Black IronIIsulphide is formed which is a compound and thus not ferromagnetic


Chemical equation Fes  Ss  FeSs Exothermic reaction H


Heated powdered heavy metals combine with sulphur to form black sulphides


Cus  Ss  CuSs


Zns  Ss  ZnSs


Pbs  Ss  PbSs


4The set up below show the reaction of sulphur on heated concentrated sulphuricVIacid


iState and explain the observation made


Observation


Yellow colour of sulphur fades


Orange colour of potassium dichromateVIpaper turns to green


Explanation


Hot concentrated sulphuricVIacid oxidizes sulphur to sulphur IVoxide gas The oxide is also reduced to water Traces of sulphur VIoxide is formed


Chemical equation


Ss  3H2 SO4 l  3SO2g  3H2Ol SO3g


Sulphur IVoxide gas turns Orange potassium dichromateVIpaper to green


iiState and explain the observation made if concentrated sulphuric VI acid is replaced with concentrated Nitric V acid in the above set up


Colurless solution formed


Brown fumesgas produced


Hot concentrated NitricVacid oxidizes sulphur to sulphuric VIacid The Nitric V acid is reduced to brown nitrogenIVoxide gas


Ss  6HNO3 l  6NO2g  2H2Ol H2SO4 l


NB


Hydrochloric acid is a weaker oxidizing agent and thus cannot oxidize sulphur like the other mineral acids


5 State three main uses of sulphur


Sulphur is mainly used in


iContact process for the manufactureindustriallarge scale production of concentrated sulphuricVIacid


iiVulcanization of rubber to make it harder tougher stronger and more durable


iiiMaking gun powder and match stick heads


iv As ointments to treat fungal infections


6 Revision Practice


The diagram below represents the extraction of sulphur by Fraschs process Use it to answer the questions that follow


aName the substances that passes through


M Superheated water at 170oC and 10 atmosphere pressure


L Hot compressed air


N Molten sulphur


bWhat is the purpose of the substance that passes through L and M


M Superheated water at 170oC and 10 atmosphere pressure is used to melt the sulphur


L Hot compressed air is used to force up the molten sulphur


c The properties of the two main allotropes of sulphur represented by letters A and B are given in the table below Use it to answer the questions that follow


IWhat are allotropes


Different forms of the same element existing at the same temperature and pressure without change of state


II Identify allotrope


Monoclinic sulphur


B  Rhombic sulphur


III State two main uses of sulphur


Manufacture of sulphuricVIacid


as fungicide


in vulcanization of rubber to make it hardertougher stronger


manufacture of dyes fibres


dCalculate the volume of sulphur IVoxide produced when 04 g of sulphur is completely burnt in excess airS  320 I mole of a gas occupies 24 dm3 at room temperature


Chemical equation


Ss  O2g  SO2g


Mole ratio S SO2  11


Method 1


320 g of sulphur  24 dm3 of SO2g


04 g of sulphur  04 g x 24 dm3  03 dm3


320 g


Method 2


Moles of sulphur used  Mass of sulphur  04  00125 moles


Molar mass of sulphur 32


Moles of sulphur used  Moles of sulphurIVoxide used00125 moles


Volume of sulphurIVoxide used  Moles of sulphurIVoxide x volume of one mole of gas 00125 moles x 24 dm3  03 dm3


BCOMPOUNDS OF SULPHUR


The following are the main compounds of sulphur


i SulphurIVoxide


ii SulphurVIoxide


iii SulphuricVIacid


iv Hydrogen Sulphide


v SulphateIVSO32 and SulphateVI SO42 salts


i SulphurIVoxideSO2


a Occurrence


Sulphur IVoxide is found in volcanic areas as a gas or dissolved in water from geysersand hot springs in active volcanic areas of the world eg Olkaria and Hells gate near Naivasha in Kenya


b School laboratory preparation


In a Chemistry school laboratory Sulphur IVoxide is prepared from the reaction of


Method 1Using Copper and SulphuricVIacid


Method 2Using Sodium SulphateIV and hydrochloric acid


cProperties of SulphurIVoxideQuestions


1 Write the equations for the reaction for the formation of sulphur IVoxide using


iMethod 1


Cus  2H2SO4l  CuSO4aq  SO2g  2H2Ol


Zns  2H2SO4l  ZnSO4aq  SO2g  2H2Ol


Mgs  2H2SO4l  MgSO4aq  SO2g  2H2Ol


Fes  2H2SO4l  FeSO4aq  SO2g  2H2Ol


Calcium Lead and Barium will form insoluble sulphateVIsalts that will cover unreacted metals stopping further reaction thus producing very small amountquantity of sulphur IVoxide gas


iiMethod 2


Na2SO3aq  HClaq  NaClaq   SO2g  2H2Ol


K2SO3aq  HClaq  KClaq   SO2g  2H2Ol


BaSO3s  2HClaq  BaCl2aq   SO2g  H2Ol


CaSO3s  2HClaq  CaCl2aq   SO2g  H2Ol


PbSO3s  2HClaq  PbCl2s   SO2g  H2Ol


LeadIIchloride is soluble on heating thus reactants should be heated to prevent it coatingcovering unreacted PbSO3s


2State the physical properties unique to sulphur IVoxide gas


Sulphur IVoxide gas is a colourless gas with a pungent irritating and choking smell which liquidifies easily It is about two times denser than air


3 The diagram below show the solubility of sulphur IVoxide gas Explain


SulphurIV oxide is very soluble in water


One drop of water dissolves all the Sulphur IV oxide in the flask leaving a vacuum


If the clip is removed atmospheric pressure forces the water up through the narrow tube to form a fountain to occupy the vacuum


An acidic solution of sulphuric IVacid is formed which turns litmus solution red


Chemical equation


SO2g  H2Ol  H2 SO3 aq  sulphuricIVacid turn litmus red


4Dry litmus papers and wetdampmoist litmus papers were put in a gas jar containing sulphurIV oxide gas State and explain the observations made


Observations


iDry Blue litmus paper remains blue


Dry red litmus paper remains red


ii Wetdampmoist blue litmus paper turns red


Moistdampwet red litmus paper remains red


Both litmus papers are then bleached decolorized


Explanation


Dry sulphurIV oxide gas is a molecular compound that does not dissociateionize to release Haqions and thus has no effect on dry bluered litmus papers


Wetdampmoist litmus papers contain water that dissolves react with dry sulphurIV oxide gas to form a solution of weak sulphuricIVacid H2 SO3 aq


Weak sulphuricIVacidH2 SO3 aq dissociates ionizes into free Haqions


H2 SO3 aq  2Haq  SO32 aq


The free Haqions are responsible for turning blue litmus paper turns red showing the gas is acidic


The SO32 aq ions in wetdampmoist sulphurIV oxide gas is responsible for many reactions of the gas


It is easilyreadily oxidized to sulphateVI SO42 aq ions making sulphurIV oxide gas act as a reducing agent as in the following examples


aBleaching agent


Wetdampmoist coloured flowerslitmus papers are bleacheddecolorized when put in sulphurIV oxide gas


This is because sulphurIV oxide removes atomic oxygen from the coloured dye material to form sulphuricVIacid


Chemical equations


iFormation of sulphuricIVacid


SO2g  H2Ol  H2 SO3 aq


iiDecolorizationbleaching of the dyeremoval of atomic oxygen


Method I H2 SO3 aq  dye  O  H2 SO4 aq  dye


coloured colourless


Method II H2 SO3 aq  dye  H2 SO4 aq  dye  O


SulphurIV oxide gas therefore bleaches by reduction removing oxygen from a dye unlike chlorine that bleaches by oxidation adding oxygen


The bleaching by removing oxygen from SulphurIV oxide gas is temporary


This is because the bleached dye regains the atomic oxygen from the atmosphereair in presence of sunlight as catalyst thus regainingrestoring its original colour eg


Old newspapers turn brown on exposure to air on regaining the atomic oxygen


The bleaching through adding oxygen by chlorine gas is permanent


bTurns Orange acidified potassium dichromateVI to green


Experiment


iPass a stream of SulphurIV oxide gas in a test tube containing acidified potassium dichromateVI solution or


iiDip a filter paper soaked in acidified potassium dichromateVI into a gas jar containing SulphurIV oxide gas


Observation


Orange acidified potassium dichromateVI turns to green


Explanation


SulphurIV oxide gas reduces acidified potassium dichromateVI from orange Cr2O72 ions to green Cr3 ions without leaving a residue itself oxidized from SO32 ions in sulphuricIV acid to SO42 ions in sulphuricVI acid


Chemicalionic equation


iReaction of SulphurIV oxide gas with water


SO2g  H2Ol  H2 SO3 aq


iiDissociation ionization of SulphuricIVacid


H2 SO3 aq  2Haq  SO32 aq


iiiOxidation of SO32 aqand reduction of Cr2O72aq


3SO32aq  Cr2O72aq 8Haq  3SO42aq  2Cr3aq  4H2Ol


This is a confirmatory test for the presence of SulphurIV oxide gas


Hydrogen sulphide also reduces acidified potassium dichromateVI from orange Cr2O72 ions to green Cr3 ions leaving a yellow residue


cDecolorizes acidified potassium manganateVII


Experiment


iPass a stream of SulphurIV oxide gas in a test tube containing acidified potassium manganateVII solution or


iiDip a filter paper soaked in acidified potassium manganateVII into a gas jar containing SulphurIV oxide gas


Observation


Purple acidified potassium manganateVII turns to colourless acidified potassium manganateVII is decolorized


Explanation


SulphurIV oxide gas reduces acidified potassium manganateVII from purple MnO4 ions to green Mn2 ions without leaving a residue itself oxidized from SO32 ions in sulphuricIV acid to SO42 ions in sulphuricVI acid


Chemicalionic equation


iiiOxidation of SO32 aqand reduction of MnO4 aq


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


purple colourless


This is another test for the presence of SulphurIV oxide gas


Hydrogen sulphide also decolorizes acidified potassium manganateVII from purple MnO4 ions to colourless Mn2 ions leaving a yellow residue


dDecolorizes bromine water


iPass a stream of SulphurIV oxide gas in a test tube containing bromine water  or


iiPut three drops of bromine water into a gas jar containing SulphurIV oxide gas Swirl


Yellow bromine water turns to colourless bromine water is decolorized


SulphurIV oxide gas reduces yellow bromine water to colourless hydrobromic acid HBr without leaving a residue itself oxidized from SO32 ions in sulphuric IV acid to SO42 ions in sulphuricVI acid


iReaction of SulphurIV oxide gas with water


SO2g  H2Ol  H2 SO3 aq


iiDissociation ionization of SulphuricIVacid


H2 SO3 aq  2Haq  SO32 aq


SO32aq  Br2 aq  H2Ol  SO42aq  2HBraq


yellow colourless


This can also be used as another test for the presence of SulphurIV oxide gas


Hydrogen sulphide also decolorizes yellow bromine water to colourless leaving a yellow residue


eReduces IronIII Fe3 salts to IronII salts Fe2


Experiment


iPass a stream of SulphurIV oxide gas in a test tube containing about 3 cm3 of Iron IIIchloride solution or


iiPlace about 3cm3 of Iron IIIchloride solution into a gas jar containing SulphurIV oxide gasSwirl


Observation


Yellowbrown Iron IIIchloride solution turns to green


Explanation


SulphurIV oxide gas reduces Iron IIIchloride solution from yellowbrown Fe3 ions to green Fe2 ions without leaving a residue itself oxidized from SO32 ions in sulphuricIV acid to SO42 ions in sulphuricVI acid


Chemicalionic equation


iiiOxidation of SO32 aqand reduction of Fe3 aq


SO32aq  2Fe3 aq 3H2Ol  SO42aq  2Fe2aq  2Haq


yellow green


fReduces NitricVacid to NitrogenIVoxide gas


iPass a stream of SulphurIV oxide gas in a test tube containing about 3 cm3 of concentrated nitricVacid or


iiPlace about 3cm3 of concentrated nitricVacid into a gas jar containing SulphurIV oxide gas Swirl


Brown fumes of a gas evolvedproduced


SulphurIV oxide gas reduces concentrated nitricVacid to brown nitrogenIVoxide gas itself oxidized from SO32 ions in sulphuricIV acid to SO42 ions in sulphuricVI acid


SO2g  2HNO3 l  H2 SO4 l  NO2 g


brown fumesgas


gReduces Hydrogen peroxide to water


Experiment


iPass a stream of SulphurIV oxide gas in a test tube containing about 3 cm3 of 20 volume hydrogen peroxide Add four drops of Barium nitrateVor Barium chloride followed by five drops of 2M hydrochloric acid 2M nitricV acid


Observation


A white precipitate is formed that persist remains on adding 2M hydrochloric acid 2M nitricV acid


Explanation


SulphurIV oxide gas reduces 20 volume hydrogen peroxide and itself oxidized from SO32 ions in sulphuricIV acid to SO42 ions in sulphuricVI acid


When Ba2 ions in Barium NitrateV or Barium chloride solution is added a white precipitate of insoluble Barium salts is formed showing the presence of of either SO32 SO42 CO32 ions ie


Chemicalionic equation


SO32aq  Ba2 aq  BaSO3s


white precipitate


SO42aq  Ba2 aq  BaSO4s


CO32aq  Ba2 aq  BaCO3s


If nitricVhydrochloric acid is added to the three suspected insoluble white precipitates above the white precipitate


i persistremains if SO42aqions BaSO4s is present


iidissolves if SO32aqions BaSO3s and CO32aqions BaCO3sis present This is because


I BaSO3s reacts with NitricVhydrochloric acid to produce acidic SO2 gas that turns Orange moist filter paper dipped in acidified Potassium dichromate to green


Chemical equation


BaSO3s 2Haq  Ba2 aq  SO2g  H2Ol


I BaCO3s reacts with NitricVhydrochloric acid to produce acidic CO2 gas that forms a white precipitate when bubbled in lime water


BaCO3s 2Haq  Ba2 aq  CO2g  H2Ol


5SulphurIVoxide also act as an oxidizing agent as in the following examples


aReduction by burning Magnesium


Experiment


Lower a burning Magnesium ribbon into agas jar containing SulphurIVoxide gas


Observation


Magnesium ribbon continues to burn with difficulty


White ash and yellow powderspeck


Explanation


SulphurIVoxide does not support burningcombustion Magnesium burns to produce enough heat energy to decompose SulphurIVoxide to sulphur and oxygen


The metal continues to burn on Oxygen forming white Magnesium oxide solidash


Yellow specks of sulphur residue form on the sides of reaction flaskgas jar


During the reaction SulphurIVoxide is reducedoxidizing agentwhile the metal is oxidized reducing agent


SO2g  2Mgs  2MgOs  Ss


white ashsolid yellow speckpowder


bReduction by Hydrogen sulphide gas


Put two drops of water into a gas jar containing dry SulphurIVoxide gas


Bubble hydrogen sulphide gas into the gas jar containing SulphurIVoxide gas


Or


Invert a gas jar full of hydrogen sulphide gas over the gas jar containing SulphurIVoxide gas Swirl


Yellow powderspeck


SulphurIVoxide oxidizes hydrogen sulphide to yellow specks of sulphur residue and itself reduced to also sulphur that form on the sides of reaction flaskgas jar


A little moisturewater act as catalyst speeds up the reaction


Chemical equation


SO2g  2H2Sg  2H2Ol  3Ss


yellow speckpowder


6SulphurIVoxide has many industrial uses State three


iIn the contact process for the manufacture of SulphuricVIacid


iiAs a bleaching agent of pulp and paper


iiiAs a fungicide to kill microbes


ivAs a preservative of jam juices to prevent fermentation


ii SulphurVIoxideSO3


a Occurrence


Sulphur VIoxide is does not occur free in natureatmosphere


b Preparation


In a Chemistry school laboratory Sulphur VIoxide may prepared from


Method 1Catalytic oxidation of sulphurIVoxide gas


SulphurIVoxide gas and oxygen mixture are first dried by being passed through Concentrated SulphuricVIacid


The dry mixture is then passed through platinised asbestos to catalysespeed up the combination to form Sulphur VIoxide gas


Sulphur VIoxide gas readily solidify as silky white needles if passed through a freezing mixture ice cold water


The solid fumes out on heating to a highly acidic poisonous gas


Chemical equation


2SO2g  O2g platinised asbestos 2SO3 g


Method 2 Heating IronIIsulphateVI heptahydrate


When green hydrated IronIIsulphateVI heptahydrate crystals are heated in a boiling tube it loses the water of crystallization and colour changes from green to white


FeSO47H2Os  FeSO4s  7H2Ol


green solid white solid


On further heating the white anhydrous IronIIsulphateVI solid decomposes to a mixture of Sulphur VIoxide and Sulphur IVoxide gas


Sulphur VI oxide readily  easily solidify as white silky needles when the mixture is passed through a freezing mixtureice cold water


IronIIIoxide is left as a brown residuesolid


2FeSO4 s  Fe2O3s  SO2 g  SO3g


green solid brown solid


Caution


On exposure to air Sulphur VIoxide gas produces highly corrosive poisonous fumes of concentrated sulphuricVIacid and thus its preparation in a school laboratory is very risky


c Uses of sulphurVIoxide


One of the main uses of sulphurVIoxide gas is as an intermediate product in the contact process for industrialmanufacturelarge scaleproduction of sulphuricVIacid


iii SulphuricVIacidH2SO4


a Occurrence


Sulphuric VIacidH2SO4 is one of the three mineral acids There are three mineral acids


NitricVacid


SulphuricVIacid


Hydrochloric acid


Mineral acids do not occur naturally but are prepared in a school laboratory and manufactured at industrial level


bThe Contact process for industrial manufacture of H2SO4


I Raw materials


The main raw materials for industrial preparation of SulphuricVIacid include


iSulphur from Fraschs process or from heating metal sulphide ore like GalenaPbSZinc blendeZnS


iiOxygen from fractional distillation of air


iiiWater from riverslakes


II Chemical processes


The contact process involves four main chemical processes


iProduction of Sulphur IVoxide


As one of the raw materials Sulphur IVoxide gas is got from the following sources


I Burningroasting sulphur in air


Sulphur from Fraschs process is roastedburnt in air to form Sulphur IVoxide gas in the burners


Chemical equation


Ss  O2g  SO2 g


II Burningroasting sulphide ores in air


Sulphur IVoxide gas is produced as a by product in extraction of some metals like


Lead from LeadIIsulphideGalenaPbS


Zinc from zincIIsulphideZinc blende ZnS


Copper from Copper iron sulphideCopper pyrites CuFeS2


On roastingburning large amount quantity of sulphurIVoxide is generatedproduced


i2PbS s  3O2 g  2PbOs  2SO2 g


ii2ZnS s  3O2 g  2ZnOs  2SO2 g


ii2CuFeS2 s  4O2 g  2FeOs  3SO2 g  Cu2Os


SulphurIVoxide easilyreadily liquefies and thus can be transported to a far distance safely


iiPurification of SulphurIVoxide


SulphurIVoxide gas contain dust particles and ArsenicIVoxide as impurities These impurities poisonimpair the catalyst by adhering oncovering its surface


The impurities are removed by electrostatic precipitation method


In the contact process Platinum or VanadiumVoxide may be used VanadiumVoxide is preferred because it is


i cheaperless expensive


ii less easily poisoned by impurities


iiiCatalytic conversion of SulphurIVoxide to SulphurVIoxide


Pure and dry mixture of Sulphur IVoxide gas and Oxygen is heated to 450oC in a heat exchanger


The heated mixture is passed through long pipes coated with pellets of Vanadium Voxide catalyst


The close contact between the reacting gases and catalyst give the process its name


Vanadium Voxide catalyse the conversionoxidation of SulphurIVoxide to SulphurVIoxide gas


Chemical equation


2SO2 g  O2g  V2O5  2SO2 g


This reaction is exothermic H and the temperatures need to be maintained at around 450oC to ensure that


ireaction ratetime taken for the formation of SulphurVIoxide is not too slowlong at lower temperatures below 450oC


ii SulphurVIoxide gas does not decompose back to SulphurIVoxide gas and Oxygen gas at higher temperatures than 450oC


ivConversion of SulphurVIoxide of SulphuricVIacid


SulphurVIoxide is the acid anhydride of concentrated SulphuricVIacid SulphurVIoxide reacts with water to form thick mist of fine droplets of veryhighly corrosive concentrated SulphuricVIacid because the reaction is highly exothermic


To prevent this Sulphur VIoxide is a passed up to meet downward flow of 98 SulphuricVIacid in the absorption chambertower


The reaction forms a very viscous oily liquid called Oleumfuming Sulphuric VI acid pyrosulphuric VI acid


H2SO4 aq  SO3 g  H2S2O7 l


Oleumfuming Sulphuric VI acid pyrosulphuric VI acid is diluted carefully with distilled water to give concentrated sulphuric VI acid


H2S2O7 l  H2O l  2H2SO4 l


The acid is stored ready for marketsale


III Environmental effects of contact process


SulphurVIoxide and SulphurIVoxide gases are atmospheric pollutants that form acid rain if they escape to the atmosphere


In the Contact process about 2 of these gases do not form sulphuric VI acid


The following precautions preventminimize pollution from Contact process


irecycling back any unreacted SulphurIVoxide gas back to the heat exchangers


iidissolving SulphurVIoxide gas in concentrated sulphuric VI acid instead of water


This prevents the formation of fine droplets of the corrosive toxicpoisonous fumes of concentrated sulphuric VI acid


iiiscrubbingThis involves passing the exhaust gases through very tall chimneys lined with quicklimecalcium hydroxide solid


This reacts with Sulphur VIoxide gas forming harmless calciumIIsulphate IV CaSO3


Chemical equation


CaOH2 aq  SO2g  CaSO3 aq  H2O g


IV Uses of SulphuricVIacid


Sulphuric VI acid is used


i in making dyes and paint


iias acid in Leadacid accumulatorbattery


iii for making soapless detergents


iv for making sulphate agricultural fertilizers


VI Sketch chart diagram showing the Contact process


c Properties of Concentrated sulphuric VI acid i Concentrated sulphuric VI acid is a colourless oily liquid with a density of 184gcm3It has a boiling point of 338oC


ii Concentrated sulphuric VI acid is very soluble in water


The solubility dissolution of the acid very highly exothermic


The concentrated acid should thus be diluted slowly in excess water


Water should never be added to the acid because the hot acid scatters highly corrosive fumes out of the container


iii Concentrated sulphuric VIacid is a covalent compound It has no free H ions


Free H ions are responsible for turning the blue litmus paper red Concentrated sulphuric VI acid thus do not change the blue litmus paper red


iv Concentrated sulphuric VIacid is hygroscopic It absorbs water from the atmosphere and do not form a solution


This makes concentrated sulphuric VI acid very suitable as drying agent during preparation of gases


vThe following are some chemical properties of concentrated sulphuric VI acid


I As a dehydrating agent


Experiment I


Put about four spatula end full of brown sugar and glucose in separate 10cm3 beaker


Carefully add about 10cm3 of concentrated sulphuric VI acid Allow to stand for about 10 minutes


Observation


Colour in brown sugar change from brown to black


Colour in glucose change from white to black


10cm3 beaker becomes very hot


Explanation


Concentrated sulphuric VI acid is strong dehydrating agent


It removes chemically and physically combined elements of waterHydrogen and Oxygen in ratio 21from compounds


When added to sugar glucose a vigorous reaction that is highly exothermic take place


The sugarglucose is charred to black mass of carbon because the acid dehydrates the sugarglucose leaving carbon


Caution


This reaction is highly exothermic that start slowly but produce fine particles of carbon that if inhaled cause quick suffocation by blocking the lung villi


Chemical equation


Glucose C6H12O6s concH2SO4 6C s  6H2Ol


white black


Sugar C12H22O11s concH2SO4 12C s 11H2Ol


brown black


Experiment II


Put about two spatula end full of hydrated copperIIsulphateVIcrystals in a boiling tube Carefully add about 10cm3 of concentrated sulphuric VI acid Warm


Observation


Colour change from blue to white


Concentrated sulphuric VI acid is strong dehydrating agentIt removes physically combined elements of waterHydrogen and Oxygen in ratio 21from hydrated compounds


The acid dehydrates blue copperIIsulphate to white anhydrous copperIIsulphate


CuSO45H2Os concH2SO4 CuSO4 s  5H2Ol


blue white


Experiment III


Put about 4cm3 of absolute ethanol in a boiling tube Carefully add about 10cm3 of concentrated sulphuric VI acid


Place moistdampwet filter paper dipped in acidified potassium dichromateVIsolution on the mouth of the boiling tube Heat strongly


Caution


Absolute ethanol is highly flammable


Colourless gas produced


Orange acidified potassium dichromate VI paper turns to green


Explanation


It removes chemically combined elements of waterHydrogen and Oxygen in ratio 21from compounds


The acid dehydrates ethanol to ethene gas at about 170oC


Ethene with CC double bond turns orange acidified potassium dichromate VI paper turns to green


Chemical equation


C2H5OHl concH2SO4170oC  C2H4 g  H2Ol


NB This reaction is used for the school laboratory preparation of ethene gas


Experiment IV


Put about 4cm3 of methanoic acid in a boiling tube Carefully add about 6 cm3 of concentrated sulphuric VI acid Heat gently


This should be done in a fume chamberopen


Observation


Concentrated sulphuric VI acid is strong dehydrating agent It removes chemically combined elements of water Hydrogen and Oxygen in ratio 21from compounds


The acid dehydrates methanoic acid to poisonoustoxic carbonIIoxide gas


HCOOHl concH2SO4  COg  H2Ol


NB This reaction is used for the school laboratory preparation of small amount carbon IIoxide gas


Experiment V


Put about 4cm3 of ethan12dioicoxalic acid in a boiling tube Carefully add about 6 cm3 of concentrated sulphuric VI acid Pass any gaseous product through lime water Heat gently


Caution


Colourless gas produced


Gas produced forms a white precipitate with lime water


Explanation


Concentrated sulphuric VI acid is strong dehydrating agent


It removes chemically combined elements of water Hydrogen and Oxygen in ratio 21from compounds


The acid dehydrates ethan12dioicoxalic acid to a mixture of poisonoustoxic carbonIIoxide and carbonIVoxide gases


Chemical equation


HOOCCOOHl concH2SO4  COg  CO2g  H2Ol


NB This reaction is also used for the school laboratory preparation of small amount carbon II oxide gas


Carbon IV oxide gas is removed by passing the mixture through concentrated sodiumpotassium hydroxide solution


II As an Oxidizing agent


Experiment I


Put about 2cm3 of Concentrated sulphuric VI acid into three separate boiling tubes Place a thin moistdampwet filter paper dipped in acidified potassium dichromate VIsolution on the mouth of the boiling tube Put about 05g of Copper turnings Zinc granule and Iron filings to each boiling tube separately


Observation


Effervescencefizzingbubbles


Blue solution formed with copper


Green solution formed with Iron


Colourless solution formed with Zinc


Colourless gas produced that has a pungent irritating choking smell


Gas produced turn orange moistdampwet filter paper dipped in acidified potassium dichromate VIsolution to green


Explanation


Concentrated sulphuric VI acid is strong oxidizing agent


It oxidizes metals to metallic sulphateVI salts and itself reduced to sulphurIVoxide gas


Sulphur IV oxide gas turn orange moistdampwet filter paper dipped in acidified potassium dichromate VIsolution to green


CuSO4aq is a blue solution ZnSO4aq is a colourless solution FeSO4aq is a green solution


Chemical equation


Cus  2H2SO4aq  CuSO4aq  SO2g  2H2Ol


Zns  2H2SO4aq  ZnSO4aq  SO2g  2H2Ol


Fes  2H2SO4aq  FeSO4aq  SO2g  2H2Ol


Experiment II


Put about 2cm3 of Concentrated sulphuric VI acid into two separate boiling tubes Place a thin moistdampwet filter paper dipped in acidified potassium dichromate VIsolution on the mouth of the boiling tube


Put about 05g of powdered charcoal and sulphur powder to each boiling tube separately


Warm


Observation


Black solid charcoal dissolvesdecrease


Yellow solid sulphur dissolvesdecrease


Concentrated sulphuric VI acid is strong oxidizing agent It oxidizes nonmetals to non metallic oxides and itself reduced to sulphurIVoxide gas Sulphur IV oxide gas turn orange moistdampwet filter paper dipped in acidified potassium dichromate VIsolution to green


Charcoal is oxidized to carbonIVoxide Sulphur is oxidized to SulphurIVoxide


Cs  2H2SO4aq  CO2aq  2SO2g  2H2Ol


Ss  2H2SO4aq  3SO2g  2H2Ol


III As the least volatile acid


Study the table below showing a comparison in boiling points of the three mineral acids


1Which is the least volatile acid Explain


SulphuricVIacidH2SO4 because it has the largest molecule and joined by Hydrogen bonds making it to have the highest boiling pointleast volatile


2 Using chemical equations explain how sulphuricVIacid displaces the less volatile mineral acids


iChemical equation


KNO3s  H2SO4aq  KHSO4l  HNO3g


NaNO3s  H2SO4aq  NaHSO4l  HNO3g


This reaction is used in the school laboratory preparation of NitricV acid HNO3


iiChemical equation


KCls  H2SO4aq  KHSO4s  HClg


NaCls  H2SO4aq  NaHSO4s  HClg


This reaction is used in the school laboratory preparation of Hydrochloric acid HCl


d Properties of dilute sulphuricVIacid


Dilute sulphuricVIacid is made when about 10cm3 of concentrated sulphuric


VI acid is carefully added to about 90cm3 of distilled water


Diluting concentrated sulphuric VI acid should be done carefully because the reaction is highly exothermic


Diluting concentrated sulphuric VI acid decreases the number of moles present in a given volume of solution which makes the acid less corrosive


On diluting concentrated sulphuricVI acid water ionizes dissociates the acid fullywholly into twodibasicfree Haq and SO42aqions


H2SO4 aq  2Haq  SO42aq


The presence of free Haqions is responsible for


iturn litmus red because of the presence of free Haqions


iihave pH 123 because of the presence of many free Haqions hence a strongly acidic solution


iiiReaction with metals


Experiment


Place 5cm3 of 02M dilute sulphuricVIacid into four separate clean test tubes Add about 01g of Magnesium ribbon to one test tube Cover the mixture with a finger as stopper Introduce a burning splint on top of the finger and release the finger stopper Repeat by adding Zinc Copper and Iron instead of the Magnesium ribbon


Observation


No effervescence bubbles fizzing with copper


Effervescence bubbles fizzing with Iron Zinc and Magnesium


Colourless gas produced that extinguishes burning splint with a pop sound


Colourless solution formed with Zinc and Magnesium


Green solution formed with Iron


Explanation


When a metal higher than hydrogen in the reactivityelectrochemical series is put in a test tube containing dilute sulphuricVIacid effervescence bubbling fizzing takes place with evolution of Hydrogen gas


Impure hydrogen gas extinguishes burning splint with a pop sound


A sulphate VI salts is formed Iron Zinc and Magnesium are higher than hydrogen in the reactivityelectrochemical series


They form Iron IIsulphateVI Magnesium sulphateVI and Zinc sulphateVI


When a metal lower than hydrogen in the reactivityelectrochemical series is put in a test tube containing dilute sulphuricVIacid there is no effervescence bubbling fizzing that take place


Copper thus do not react with dilute sulphuricVIacid


Chemicalionic equation


Mgs  H2SO4aq  MgSO4aq  H2g


Mgs  2Haq  Mg2 aq  H2g


Zns  H2SO4aq  ZnSO4aq  H2g


Zns  2Haq  Zn2 aq  H2g


Fes  H2SO4aq  FeSO4aq  H2g


Fes  Haq  Fe2 aq  H2g


NBi CalciumLead and Barium forms insoluble sulphateVIsalts that covercoat the unreacted metals


iiSodium and Potassium react explosively with dilute sulphuricVIacid


ivReaction with metal carbonates and hydrogen carbonates


Experiment


Place 5cm3 of 02M dilute sulphuricVIacid into four separate clean boiling tubes Add about 01g of sodium carbonate to one boiling tube Introduce a burning splint on top of the boiling tube Repeat by adding Zinc carbonate Copper IIcarbonate and IronIICarbonate in place of the sodium hydrogen carbonate


Observation


Effervescence bubbles fizzing


Colourless gas produced that extinguishes burning splint


Colourless solution formed with Zinc carbonate sodium hydrogen carbonate and sodium carbonate


Green solution formed with IronIICarbonate


Blue solution formed with CopperIICarbonate


Explanation


When a metal carbonate or a hydrogen carbonates is put in a test tube containing dilute sulphuricVIacid effervescence bubbling fizzing takes place with evolution of carbonIVoxide gas carbonIVoxide gas extinguishes a burning splint and forms a white precipitate when bubbled in lime water


A sulphate VI salts is formed


Chemicalionic equation


ZnCO3s  H2SO4aq  ZnSO4aq  H2Ol  CO2g


ZnCO3s  2Haq  Zn2 aq  H2Ol  CO2g


CuCO3s  H2SO4aq  CuSO4aq  H2Ol  CO2g


CuCO3s  2Haq  Cu2 aq  H2Ol  CO2g


FeCO3s  H2SO4aq  FeSO4aq  H2Ol  CO2g


FeCO3s  2Haq  Fe2 aq  H2Ol  CO2g


2NaHCO3s  H2SO4aq  Na2SO4aq  2H2Ol  2CO2g


NaHCO3s  Haq  Na aq  H2Ol  CO2g


Na2CO3s  H2SO4aq  Na2SO4aq  H2Ol  CO2g


NH42CO3s  H2SO4aq  NH42SO4 aq  H2Ol  CO2g


NH42CO3 s  Haq  NH4 aq  H2Ol  CO2g


2NH4HCO3aq  H2SO4aq  NH42SO4 aq  H2Ol  CO2g


NH4HCO3aq  Haq  NH4 aq  H2Ol  CO2g


NB


Calcium Lead and Barium carbonates forms insoluble sulphateVIsalts that covercoat the unreacted metals


vNeutralizationreaction of metal oxides and alkalisbases


Experiment I


Place 5cm3 of 02M dilute sulphuricVIacid into four separate clean boiling tubes Add about 01g of copperIIoxide to one boiling tube Stir


Repeat by adding Zinc oxide calcium carbonate and Sodium IIOxide in place of the CopperIIOxide


Observation


Blue solution formed with CopperIIOxide


Colourless solution formed with other oxides


Explanation


When a metal oxide is put in a test tube containing dilute sulphuricVIacid the oxide dissolves forming a sulphate VI salt


Chemicalionic equation


ZnOs  H2SO4aq  ZnSO4aq  H2Ol


ZnOs  2Haq  Zn2 aq  H2Ol


CuOs  H2SO4aq  CuSO4aq  H2Ol


CuOs  2Haq  Cu2 aq  H2Ol


MgOs  H2SO4aq  MgSO4aq  H2Ol


MgOs  2Haq  Mg2 aq  H2Ol


Na2Os  H2SO4aq  Na2SO4aq  H2Ol


Na2Os  2Haq  2Na aq  H2Ol


K2CO3s  H2SO4aq  K2SO4aq  H2Ol


K2Os  Haq  2K aq  H2Ol


NB


Calcium Lead and Barium oxides forms insoluble sulphateVIsalts that covercoat the unreacted metals oxides


Experiment II


Fill a burette with 01M dilute sulphuricVIacid Pipette 200cm3 of 01Msodium hydroxide solution into a 250cm3 conical flask Add three drops of phenolphthalein indicator Titrate the acid to get a permanent colour change Repeat with01M potassium hydroxide solution inplace of 01Msodium hydroxide solution


Observation


Colour of phenolphthalein changes from pink to colourless at the end point


Explanation


Like other mineral acids dilute sulphuricVIacid neutralizes basesalkalis to a sulphate salt and water only


Colour of the indicator used changes when a slight excess of acid is added to the base at the end point


Chemical equation


2NaOHaq  H2SO4aq  Na2SO4aq  H2Ol


OHs  Haq  H2Ol


2KOHaq  H2SO4aq  K2SO4aq  H2Ol


2NH4OHaq  H2SO4aq  NH42SO4aq  H2Ol


iv Hydrogen sulphideH2S


a Occurrence


Hydrogen sulphide is found in volcanic areas as a gas or dissolved in water from geysers and hot springs in active volcanic areas of the world eg Olkaria and Hells gate near Naivasha in Kenya


It is present in rotten eggs and human excreta


b Preparation


Hydrogen sulphide is prepared in a school laboratory by heating Iron II sulphide with dilute hydrochloric acid


c Properties of Hydrogen sulphideQuestions


1 Write the equation for the reaction for the school laboratory preparation of Hydrogen sulphide


Chemical equation FeS s  2HCl aq  H2S g FeCl2 aq


2 State three physical properties unique to Hydrogen sulphide


Hydrogen sulphide is a colourless gas with characteristic pungent poisonous smell of rotten eggs It is soluble in cold water but insoluble in warm water It is denser than water and turns blue litmus paper red


3 Hydrogen sulphide exist as a dibasic acid when dissolved in water Using a chemical equation show how it ionizes in aqueous state


H2Saq  Haq  HSaq


H2Saq  2Haq  S2 aq


Hydrogen sulphide therefore can form both normal and acid salts eg


Sodium hydrogen sulphide and sodium sulphide both exist


4 State and explain one gaseous impurity likely to be present in the gas jar containing hydrogen sulphide above


Hydrogen H2


IronIIsulphide contains Iron as impurity The iron will react with dilute hydrochloric acid to form ironIIchloride and produce hydrogen gas that mixes with hydrogen sulphide gas


5 State and explain the observations made when a filter paper dipped in LeadII ethanoate Lead II nitrateV solution is put in a gas jar containing hydrogen sulphide gas


Observations


Moist LeadII ethanoate Lead II nitrateV paper turns black


Explanation


When hydrogen sulphide is bubbled in a metallic salt solution a metallic sulphide is formed


All sulphides are insoluble black salts except sodium sulphide potassium sulphide and ammonium sulphides


Hydrogen sulphide gas blackens moist Lead II ethanoate Lead II nitrateV paper


The gas reacts with Pb2 in the paper to form black LeadIIsulphide


This is the chemical test for the presence of H2S other than the physical smell of rotten eggs


Chemical equations


Pb2aq  H2S  PbS  2Haq


black


Fe2aq  H2S  FeS  2Haq


Zn2aq  H2S  ZnS  2Haq


Cu2aq  H2S  CuS  2Haq


2Cuaq  H2S  Cu2S  2Haq


6 Dry hydrogen sulphide was ignited as below


i State the observations made in flame A


Hydrogen sulphide burns in excess air with a blue flame to form sulphurIVoxide gas and water


Chemical equation 2H2Sg  3O2g  2H2Ol  2SO2g


Hydrogen sulphide burns in limited air with a blue flame to form sulphur solid and water


Chemical equation 2H2Sg  O2g  2H2Ol  2Ss


7 Hydrogen sulphide is a strong reducing agent that is oxidized to yellow solid sulphur as precipitate The following experiments illustrate the reducing properties of Hydrogen sulphide


aTurns Orange acidified potassium dichromateVI to green


Experiment


iPass a stream of Hydrogen sulphide gas in a test tube containing acidified potassium dichromate VI solution or


iiDip a filter paper soaked in acidified potassium dichromate VI into a gas jar containing Hydrogen sulphide gas


Observation


Orange acidified potassium dichromate VI turns to green


Yellow solid residue


Explanation


Hydrogen sulphide gas reduces acidified potassium dichromateVI from orange Cr2O72 ions to green Cr3 ions leaving a yellow solid residue as itself is oxidized to sulphur


Chemicalionic equation


4H2Saq  Cr2O72aq 6Haq  4Saq  2Cr3aq  7H2Ol


This test is used for differentiating Hydrogen sulphide and sulphur IVoxide gas


SulphurIVoxide also reduces acidified potassium dichromateVI from orange Cr2O72 ions to green Cr3 ions without leaving a yellow residue


bDecolorizes acidified potassium manganateVII


iPass a stream of SulphurIV oxide gas in a test tube containing acidified potassium manganateVII solution or


iiDip a filter paper soaked in acidified potassium manganateVII into a gas jar containing Hydrogen Sulphide gas


Purple acidified potassium manganateVII turns to colourless acidified potassium manganateVII is decolorized


Hydrogen sulphide gas reduces acidified potassium manganateVII from purple MnO4 ions to green Mn2 ions leaving a residue as the gas itself is oxidized to sulphur


5H2Sg  2MnO4 aq 6Haq  5S s  2Mn2aq  8H2Ol


purple colourless


This is another test for differentiating Hydrogen sulphide and SulphurIV oxide gas


SulphurIV oxide also decolorizes acidified potassium manganateVII from purple MnO4 ions to colourless Mn2 ions leaving no yellow residue


cDecolorizes bromine water


Experiment


iPass a stream of Hydrogen sulphide gas in a test tube containing bromine water  or


iiPut three drops of bromine water into a gas jar containing Hydrogen sulphide gas Swirl


Observation


Yellow bromine water turns to colourless bromine water is decolorized


Yellow solid residue


Explanation


Hydrogen sulphide gas reduces yellow bromine water to colourless hydrobromic acid HBr leaving a yellow residue as the gas itself is oxidized to sulphur


Chemicalionic equation


H2 Sg  Br2 aq  S s  2HBraq


yellow solution yellow solid colourless


dReduces IronIII Fe3 salts to IronII salts Fe2


iPass a stream of Hydrogen sulphide gas in a test tube containing about 3 cm3 of Iron IIIchloride solution or


iiPlace about 3cm3 of Iron IIIchloride solution into a gas jar containing Hydrogen sulphide gas Swirl


Yellowbrown Iron IIIchloride solution turns to green


Yellow solid


Hydrogen sulphide gas reduces Iron IIIchloride solution from yellowbrown Fe3 ions to green Fe2 ions leaving a yellow residueThe gas is itself oxidized to sulphur


H2Saq  2Fe3 aq  S s  Fe2aq  2Haq


yellow solution yellow residue green


eReduces NitricVacid to NitrogenIVoxide gas


Experiment


iPass a stream of Hydrogen sulphide gas in a test tube containing about 3 cm3 of concentrated nitricVacid or


iiPlace about 3cm3 of concentrated nitricVacid into a gas jar containing Hydrogen sulphide gas Swirl


Observation


Brown fumes of a gas evolvedproduced


Yellow solid residue


Explanation


Hydrogen sulphide gas reduces concentrated nitricVacid to brown nitrogenIVoxide gas itself oxidized to yellow sulphur


Chemicalionic equation


H2Sg  2HNO3 l  2H2Ol  S s  2NO2 g


yellow residue brown fumes


fReduces sulphuricVIacid to Sulphur


iPass a stream of Hydrogen sulphide gas in a test tube containing about 3 cm3 of concentrated sulphuricVIacid or


iiPlace about 3cm3 of concentrated sulphuric VI acid into a gas jar containing Hydrogen sulphide gas Swirl


Hydrogen sulphide gas reduces concentrated sulphuricVIacid to yellow sulphur


3H2Sg  H2SO4 l  4H2Ol  4S s


yellow residue


gReduces Hydrogen peroxide to water


Experiment


iPass a stream of Hydrogen sulphide gas in a test tube containing about 3 cm3 of 20 volume hydrogen peroxide


Observation


Hydrogen sulphide gas reduces 20 volume hydrogen peroxide to water and itself oxidized to yellow sulphur


H2Sg  H2O2 l  2H2Ol  S s


8Name the salt formed when


iequal volumes of equimolar hydrogen sulphide neutralizes sodium hydroxide solution


Sodium hydrogen sulphide


Chemicalionic equation


H2Sg  NaOH l  H2Ol  NaHS aq


ii hydrogen sulphide neutralizes excess concentrated sodium hydroxide solution


Sodium sulphide


H2Sg  2NaOH l  2H2Ol  Na2S aq


Practice


Hydrogen sulphide gas was bubbled into a solution of metallic nitrateVsalts as in the flow chart below


aName the black solid CopperIIsulphide


bIdentify the cation responsible for the formation of


I Blue solution Cu2aq


II Green solution Fe2aq


III Brown solution Fe3aq


cUsing acidified potassium dichromateVI describe how you would differentiate between sulphurIVOxide and hydrogen sulphide


Bubble the gases in separate test tubes containing acidified Potassium dichromateVI solution


Both changes the Orange colour of acidified Potassium dichromateVI solution to green


Yellow solid residuedeposit is formed with Hydrogen sulphide


4H2Saq  Cr2O72aq 6Haq  4Saq  2Cr3aq  7H2Ol


3SO32aq  Cr2O72aq 8Haq  3SO42aq  2Cr3aq  4H2Ol


dState and explain the observations made if a burning splint is introduced at the mouth of a hydrogen sulphide generator


Observation


Gas continues burning with a blue flame


Explanation Hydrogen sulphide burns in excess air with a blue flame to form sulphurIVoxide gas and water


Chemical equation 2H2Sg 3O2g  2H2Ol  2SO2 g


vSulphate VI SO42and SulphateIV SO32 salts


1 Sulphate VI SO42 salts are normal and acid salts derived from Sulphuric VIacid H2SO4


2 SulphateIV SO32 salts are normal and acid salts derived from Sulphuric IVacid H2SO3


3 Sulphuric VIacid H2SO4 is formed when sulphurVIoxide gas is bubbled in water


The acid exist as a dibasic acid with two ionisable hydrogen It forms therefore the Sulphate VI SO42 and hydrogen sulphate VI HSO4 salts


ie


H2SO4 aq  2Haq  SO42aq


H2SO4 aq  Haq  HSO4 aq


All Sulphate VI SO42 salts dissolve in waterare soluble except Calcium II sulphate VI CaSO4 Barium II sulphate VI BaSO4 and Lead II sulphate VI PbSO4


All Hydrogen sulphate VI HSO3 salts exist in solutiondissolved in water Sodium I hydrogen sulphate VI NaHSO4 Potassium I hydrogen sulphate VI KHSO4 and Ammonium hydrogen sulphate VI NH4HSO4 exist also as solids


Other Hydrogen sulphate VI HSO4 salts do not exist except those of Calcium II hydrogen sulphate VI Ca HSO42 and Magnesium II hydrogen sulphate VI Mg HSO42


4 Sulphuric IVacid H2SO3 is formed when sulphurIVoxide gas is bubbled in water


The acid exist as a dibasic acid with two ionisable hydrogen It forms therefore the Sulphate IV SO32 and hydrogen sulphate VI HSO4 salts


H2SO3 aq  2Haq  SO32aq


H2SO3 aq  Haq  HSO3 aq


All Sulphate IV SO32 salts dissolve in waterare soluble except Calcium II sulphate IV CaSO3 Barium II sulphate IV BaSO3 and Lead II sulphate IV PbSO3


All Hydrogen sulphate IV HSO3 salts exist in solutiondissolved in water Sodium I hydrogen sulphate IV NaHSO3 Potassium I hydrogen sulphate IV KHSO3 and Ammonium hydrogen sulphate IV NH4HSO3 exist also as solids


Other Hydrogen sulphate IV HSO3 salts do not exist except those of Calcium II hydrogen sulphate IV Ca HSO32 and Magnesium II hydrogen sulphate IV Mg HSO32


5The following experiments show the effect of heat on sulphateVI SO42and sulphateIV SO32 salts


Experiment


In a clean dry test tube place separately about 10g of


ZincIIsulphate VI IronIIsulphateVI CopperIIsulphateVISodium I sulphate VI Sodium I sulphate IVHeat gently then strongly Test any gases produced using litmus papers


Observations


Colourless droplets of liquid forms on the cooler parts of the test tube in all cases


White solid residue is left in case of Zinc IIsulphateVISodium I sulphate VI and Sodium I sulphate IV


Colour changes from green to brown yellow in case of Iron IIsulphateVI


Colour changes from blue to white then black in case of Copper II sulphate VI


Blue litmus paper remain and blue and red litmus paper remain red in case of ZincIIsulphateVI Sodium I sulphate VI and Sodium I sulphate IV


Blue litmus paper turns red and red litmus paper remain red in case of Iron IIsulphateVI and Copper II sulphate VI


Explanation


iAll Sulphate VI SO42 salts exist as hydrated salts with water of crystallization that condenses and collects on cooler parts of test tube as a colourless liquid on gentle heating eg


K2SO410H2Os  K2SO4s  10H2Ol


Na2SO410H2Os  Na2SO4s  10H2Ol


MgSO47H2Os  MgSO4s  7H2Ol


CaSO47H2Os  CaSO4s  7H2Ol


ZnSO47H2Os  ZnSO4s  7H2Ol


FeSO47H2Os  FeSO4s  7H2Ol


Al2SO436H2Os  Al2SO43 s  6H2Ol


CuSO45H2Os  CuSO4s  5H2Ol


All Sulphate VI SO42 salts do not decompose on heating except Iron II sulphate VI and Copper II sulphate VI


iIron II sulphate VI decomposes on strong heating to produce acidic sulphur IVoxide and sulphurVIoxide gases IronIIIoxide is formed as a brown yellow residue


Chemical equation


2FeSO4 s  Fe2O3s  SO2g  SO3g


This reaction is used for the school laboratory preparation of small amount of sulphurVIoxide gas


Sulphur VI oxide readily easily solidifies as white silky needles when the mixture is passed through freezing mixtureice cold water


Sulphur IV oxide does not


ii CopperIIsulphateVI decomposes on strong heating to black copper II oxide and Sulphur VI oxide gas


2CuSO4 s  CuOs  SO3g


6 The following experiments show the test for the presence of sulphate VI SO42and sulphateIV SO32 ions in a sample of a saltcompound


ExperimentsObservations


aUsing LeadIInitrateV


I To about 5cm3 of a salt solution in a test tube add four drops of LeadIInitrateVsolution Preserve


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


Observation 1


Observation 2


IIIaTo the preserved sample observation 1 in II above Heat to boil


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


bUsing BariumIInitrateV BariumIIchloride


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


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


Explanations


Using LeadIInitrateV


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


Chemicalionic equation


Pb2aq  Cl aq  PbCl2s


Pb2aq  SO42 aq  PbSO4 s


Pb2aq  SO32 aq  PbSO3 s


Pb2aq  CO32 aq  PbCO3 s


iiWhen the insoluble precipitates are acidified with nitricV acid


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


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


PbSO3 s  2Haq  H2 O l  Pb2aq  SO2 g


PbCO3 s  2Haq  H2 O l  Pb2aq  CO2 g


iiiWhen LeadIIchloride and LeadIIsulphateVI are heatedwarmed


LeadIIchloride dissolves in hot wateron boilingrecrystallizes on cooling


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


ivWhen sulphurIVoxide and carbonIVoxide gases are produced


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


Chemical equation


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


purple colourless


3SO32aq  Cr2O72aq 8Haq  3SO42aq  2Cr3aq  4H2Ol


Orange green


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


CaOH2aq  CO2 g  CaCO3s  H2Ol


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


Using BariumIInitrateV BariumIIChloride


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


Chemicalionic equation


Ba2aq  SO42 aq  BaSO4 s


Ba2aq  SO32 aq  BaSO3 s


Ba2aq  CO32 aq  BaCO3 s


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


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


BaSO3 s  2Haq  H2 O l  Ba2aq  SO2 g


BaCO3 s  2Haq  H2 O l  Ba2aq  CO2 g


iii When sulphurIVoxide and carbonIVoxide gases are produced


Chemical equation


purple colourless


Orange green


Summary test for Sulphate VI SO42and SulphateIV SO32 salts


Practice revision question


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


aIdentify the


I Sodium salt solution


Sodium sulphateIVNa2SO3


II White precipitate


Barium sulphateIVBaSO3


III Gas G


Sulphur IVOxide SO2


IV Colourless solution H


Barium chloride BaCl2


bWrite an ionic equation for the formation of IWhite precipitate


Ionic equation Ba2aq  SO32aq  BaSO3s


IIGas G


Ionic equation BaSO3s 2Haq  SO2 g  H2O l  Ba2aq


III Green solution from the orange solution


Orange green


2 Study the flow chart below and answer the questions that follow


iWrite equation for the reaction taking place at


IThe roasting furnace 1mk


2FeS2 s  5O2 g  2FeOs  4SO2 g


IIThe absorption tower 1mk


H2SO4 l  SO3 g  H2S2O7l


IIIThe diluter 1mk


H2S2O7l  H2 Ol  2H2SO4 l


iiThe reaction taking place in chamber K is


SO2 g  12O2 g SO3 g


I Explain why it is necessary to use excess air in chamber K


To ensure all the SO2 reacts


IIName another substance used in chamber K


VanadiumVoxide


3aDescribe a chemical test that can be used to differentiate between sodium sulphate IV and sodium sulphate VI


Add acidified Barium nitrateVchloride


White precipitate formed with sodium sulphate VI


No white precipitate formed with sodium sulphate IV


bCalculate the volume of sulphur IV oxide formed when 120 kg of copper is reacted with excess concentrated sulphuricVIacidCu  635 1 mole of a gas at stp 224dm3


Chemical equation


Cus  2H2SO4l  CuSO4aq H2Ol  SO2 g


Mole ratio Cus SO2 g  11


Method 1


1 Mole Cu 635 g  1 mole SO2  224dm3


120 x 1000 g  120 x 1000 g x 224dm3


635 g


Method 2


Moles of Cu   120 x 1000  g 18897639 moles


Moles SO2  Moles of Cu  18897639 moles


Volume of SO2  Mole x molar gas volume  18897639 moles x 224


aIdentify the


ication responsible for the green solution T


iipossible anions present in white precipitate R


CO32 SO32 SO42


bName gas V


Sulphur IVoxide


cWrite a possible ionic equation for the formation of white precipitate R


Ba2 aq  CO32 aq  BaCO3s


Ba2 aq  SO32 aq  BaSO3s


Ba2 aq  SO42 aq  BaSO4s


ORGANIC CHEMISTRY 1  2


Introduction to Organic chemistry


Organic chemistry is the branch of chemistry that studies carbon compounds present in living things once living things or syntheticmanmade


Compounds that makes up living things whether alive or dead mainly contain carbon Carbon is tetravalent


It is able to form stable covalent bonds with itself and many nonmetals like hydrogen nitrogen oxygen and halogens to form a variety of compounds This is because


i carbon uses all the four valence electrons to form four strong covalent bond


iicarbon can covalently bond to form a single double or triple covalent bond with itself


iiicarbon atoms can covalently bond to form a very long chain or ring


When carbon covalently bond with Hydrogen it forms a group of organic compounds called Hydrocarbons


AHYDROCARBONS HCs


Hydrocarbons are a group of organic compounds containing made up of hydrogen and carbon atoms only


Depending on the type of bond that exist between the individual carbon atoms hydrocarbon are classified as


i Alkanes


ii Alkenes


iii Alkynes


aNomenclatureNaming


These are hydrocarbons with a general formula CnH2n2 where n is the number of Carbon atoms in a molecule


The carbon atoms are linked by single bond to each other and to hydrogen atoms


They include


Note


1The general formulamolecular formular of a compound shows the number of each atoms of elements making the compound eg


Decane has a generalmolecular formula C10H22 this means there are 10 carbon atoms and 22 hydrogen atoms in a molecule of decane


2The structural formula shows the arrangementbonding of atoms of each element making the compound eg


Decane has the structural formula as in the table above this means the 1st carbon from left to right is bonded to three hydrogen atoms and one carbon atom


The 2nd carbon atom is joinedbonded to two other carbon atoms and two Hydrogen atoms


3Since carbon is tetravalent each atom of carbon in the alkane MUST always be bonded using four covalent bond four shared pairs of electrons


4Since Hydrogen is monovalent each atom of hydrogen in the alkane MUST always be bonded using one covalent bondone shared pair of electrons


5One member of the alkane differ from the nextprevious by a CH2 group


eg


Propane differ from ethane by one carbon and two Hydrogen atoms form ethane Ethane differ from methane also by one carbon and two Hydrogen atoms


6A group of compounds that differ by a CH2 group from the next previous consecutively is called a homologous series


7A homologous series


i differ by a CH2 group from the next previous consecutively


iihave similar chemical properties


iiihave similar chemical formula that can be represented by a general formula eg alkanes have the general formula CnH2n2


ivthe physical properties egmeltingboiling pointsshow steady gradual change


8The 1st four alkanes have the prefix methethprop and but to represent 123 and 4 carbons in the compound All other use the numeral prefix pentHexhept  etc to show also the number of carbon atoms


9If one hydrogen atom in an alkane is removed an alkyl group is formedeg


bIsomers of alkanes


Isomers are compounds with the same molecular general formula but different molecular structural formula


Isomerism is the existence of a compounds having the same generalmolecular formula but different structural formula


The 1st three alkanes do not form isomersIsomers are named by using the IUPACInternational Union of Pure and Applied Chemistry system of nomenclaturenaming


The IUPAC system of nomenclature uses the following basic rulesguidelines


1Identify the longest continuous carbon chain to getdetermine the parent alkane


2Number the longest chain form the end of the chain that is near the branches so as the branch get the lowest number possible


3 Determine the position number and type of branches Name them as methyl ethyl propyl etc according to the number of carbon chains attached to the parent alkane Name them fluorochlorobromoiodo if they are halogens


4Use prefix ditritetrapentahexa to show the number of branches attached to the parent alkane


Practice on IUPAC nomenclature of alkanes


aDraw the structure of


Procedure


1 Identify the longest continuous carbon chain to getdetermine the parent alkane


Butane is the parent name CH3 CH2 CH2 CH3


2 Number the longest chain form the end of the chain that is near the branches so as the branch get the lowest number possible


The methyl group is attached to Carbon 2


3 Determine the position number and type of branches Name them as methyl ethyl propyl etc according to the number of carbon chains attached to the parent alkane ie


Position of the branch at carbon 2


Number of branches at carbon 1


Type of the branch methyl hence


Molecular formula


CH3 CH CH2 CH3  CH3 CH CH3  CH2CH3


Structural formula


H H H H


H C C C C H


H H H


H C H


H


Procedure


Number of branches at carbon 2


Type of the branch twomethyl hence


Molecular formular


CH3 C CH2 CH3  CH3 C CH3 2 CH2CH3


iii 223trimethylbutane


The methyl group is attached to Carbon 2 and 3


Position of the branch at carbon 2 and 3


Number of branches at carbon 3


Type of the branch three methyl hence


CH3 C CH CH3  CH3 C CH3 3 CH2CH3


CH3 CH3


Structural formula


H H


H C C C H


H C C H


H


H C H


iv 111222hexabromoethane


Molecular formula


CBr3 CBr3


Br Br


Br C C Br


v 111tetrachloro22dimethylbutane


CCl 3 C CH3  C Cl 3 C CH3 2 CH3


Cl


Cl C Cl


cOccurrence and extraction


Crude oil natural gas and biogas are the main sources of alkanes


iNatural gas is found on top of crude oil deposits and consists mainly of methane


iiBiogas is formed from the decay of waste organic products like animal dung and cellulose When the decay takes place in absence of oxygen  6075 by volume of the gaseous mixture of methane gas is produced


iiiCrude oil is a mixture of many flammable hydrocarbonssubstances Using fractional distillation each hydrocarbon fraction can be separated from the other The hydrocarbon with lower smaller number of carbon atoms in the chain have lower boiling point and thus collected first


As the carbon chain increase the boiling point viscosity ease of flow and colour intensity increase as flammability decrease Hydrocarbons in crude oil are not pure They thus have no sharp fixed boiling point


Uses of different crude oil fractions


dSchool laboratory preparation of alkanes


In a school laboratory alkanes may be prepared from the reaction of a sodium alkanoate with solid sodium hydroxidesoda lime


Chemical equation


Sodium alkanoate  soda lime  alkane  Sodium carbonate


CnH2n1COONas  NaOHs  C n H2n2  Na2CO3s


The H in NaOH is transferredmoves to the CnH2n1 in CnH2n1COONas to form C n H2n2


Examples


1 Methane is prepared from the heating of a mixture of sodium ethanoate and soda lime and collecting over water


Sodium ethanoate  soda lime  methane  Sodium carbonate


CH3COONas  NaOHs  C H4  Na2CO3s


The H in NaOH is transferredmoves to the CH3 in CH3COONas to form CH4


2 Ethane is prepared from the heating of a mixture of sodium propanoate and soda lime and collecting over water


Sodium propanoate  soda lime  ethane  Sodium carbonate


CH3 CH2COONas  NaOHs  CH3 CH3  Na2CO3s


The H in NaOH is transferredmoves to the CH3 CH2 in CH3 CH2COONa s to form CH3 CH3


3 Propane is prepared from the heating of a mixture of sodium butanoate and soda lime and collecting over water


Sodium butanoate  soda lime  propane  Sodium carbonate


CH3 CH2CH2COONas  NaOHs  CH3 CH2CH3  Na2CO3s


The H in NaOH is transferredmoves to the CH3 CH2 CH2 in CH3 CH2CH2COONa s to form CH3 CH2CH3


4 Butane is prepared from the heating of a mixture of sodium pentanoate and soda lime and collecting over water


Sodium pentanoate  soda lime  butane  Sodium carbonate


CH3 CH2 CH2CH2COONasNaOHs  CH3 CH2CH2CH3  Na2CO3s


The H in NaOH is transferredmoves to the CH3CH2 CH2 CH2 in CH3 CH2CH2 CH2COONa s to form CH3 CH2 CH2CH3


Laboratory set up for the preparation of alkanes


dProperties of alkanes


I Physical properties


Alkanes are colourless gases solids and liquids that are not poisonous


They are slightly soluble in water


The solubility decrease as the carbon chain and thus the molar mass increase


The melting and boiling point increase as the carbon chain increase


This is because of the increase in vanderwaals intermolecular forces as the carbon chain increase


The 1st four straight chain alkanes methaneethanepropane and butaneare therefore gases the nect sixpentane hexane heptaneoctanenonane and decane are liquids while the rest from unidecane11 carbon atoms are solids


The density of straight chain alkanes increase with increasing carbon chain as the intermolecular forces increases


This reduces the volume occupied by a given mass of the compound


Summary of physical properties of alkanes


IIChemical properties


iBurning


Alkanes burn with a bluenonluminous nonsootynonsmoky flame in excess air to form carbonIV oxide and water


Alkane  Air  carbonIV oxide  water excess airoxygen


Alkanes burn with a bluenonluminous nosootynonsmoky flame in limited air to form carbonII oxide and water


Alkane  Air  carbonII oxide  water limited air


Examples


1a Methane when ignited burns with a blue non sooty flame in excess air to form carbonIV oxide and water


Methane  Air  carbonIV oxide  water excess airoxygen


CH4g  2O2g  CO2g  2H2Olg


b Methane when ignited burns with a blue non sooty flame in limited air to form carbonII oxide and water


Methane  Air  carbonII oxide  water excess airoxygen


2CH4g  3O2g  2COg  4H2Olg


2a Ethane when ignited burns with a blue non sooty flame in excess air to form carbonIV oxide and water


Ethane  Air  carbonIV oxide  water excess airoxygen


2C2H6g  7O2g  4CO2g  6H2Olg


b Ethane when ignited burns with a blue non sooty flame in limited air to form carbonII oxide and water


Ethane  Air  carbonII oxide  water excess airoxygen


2C2H6g  5O2g  4COg  6H2Olg


3a Propane when ignited burns with a blue non sooty flame in excess air to form carbonIV oxide and water


Propane  Air  carbonIV oxide  water excess airoxygen


C3H8g  5O2g  3CO2g  4H2Olg


2C3H8g  7O2g  6COg  8H2Olg


iiSubstitution


Substitution reaction is one in which a hydrogen atom is replaced by a halogen in presence of ultraviolet light


Alkanes react with halogens in presence of ultraviolet light to form halogenoalkanes


During substitution


ithe halogen molecule is split into free atomradicals


iione free halogen radicalatoms knock remove one hydrogen from the alkane leaving an alkyl radical


iii the alkyl radical combine with the other free halogen atomradical to form halogenoalkane


ivthe chlorine atoms substitute repeatedly in the alkane Each substitution removes a hydrogen atom from the alkane and form hydrogen halide


vsubstitution stops when all the hydrogen in alkanes are replaced with halogens


Substitution reaction is a highly explosive reaction in presence of sunlight  ultraviolet light that act as catalyst


Examples of substitution reactions


Methane has no effect on bromine or chlorine in diffused lightdark In sunlight  a mixture of chlorine and methane explode to form colourless mixture of chloromethane and hydrogen chloride gas The pale green colour of chlorine gas fades


Chemical equation


1aMethane  chlorine  Chloromethane  Hydrogen chloride


CH4g  Cl2g  CH3Cl g  HCl g


H H


H C H  Cl Cl  H C Cl  H Cl


b Chloromethane  chlorine  dichloromethane  Hydrogen chloride


CH3Cl g  Cl2g  CH2Cl2 g  HCl g


H C Cl  Cl Cl  H C Cl  H Cl


H Cl


c dichloromethane  chlorine  trichloromethane  Hydrogen chloride


CH2Cl2 g  Cl2g  CHCl3 g  HCl g


Cl H


H C Cl  Cl Cl  Cl C Cl  H Cl


c trichloromethane  chlorine  tetrachloromethane  Hydrogen chloride


CHCl3 g  Cl2g  CCl4 g  HCl g


Cl C Cl  Cl Cl  Cl C Cl  H Cl


Cl Cl


Ethane has no effect on bromine or chlorine in diffused lightdark In sunlight  a mixture of bromine and ethane explode to form colourless mixture of bromoethane and hydrogen chloride gas The redbrown colour of bromine gas fades


Chemical equation


aEthane  chlorine  Chloroethane  Hydrogen chloride


CH3CH3g  Br2g  CH3CH2Br g  HBr g


H H H H


H C C H  Br Br  H C C H  H Br


H H H Br


Bromoethane


H Br H Br


H C C H  Br Br  H C C Br  H Br


H C C Br  Br Br  H C C Br  H Br


H Br Br Br


H C C Br  Br Br  Br C C Br  H Br


Br Br Br Br


Br C C Br  Br Br  Br C C Br  H Br


Uses of alkanes


1Most alkanes are used as fuel eg Methane is used as biogas in homes Butane is used as the Laboratory gas


2On cracking alkanes are a major source of Hydrogen for the manufacture of ammoniaHaber process


3In manufacture of Carbon black which is a component in printers ink


4In manufacture of useful industrial chemicals like methanol methanol and chloromethane


ii Alkenes


aNomenclatureNaming


These are hydrocarbons with a general formula CnH2n and C C double bond as the functional group  n is the number of Carbon atoms in the molecule


The carbon atoms are linked by at least one double bond to each other and single bonds to hydrogen atoms


They include


Note


1Since carbon is tetravalent each atom of carbon in the alkene MUST always be bonded using four covalent bond four shared pairs of electrons including at the double bond


2Since Hydrogen is monovalent each atom of hydrogen in the alkene MUST always be bonded using one covalent bondone shared pair of electrons


3One member of the alkene like alkanesdiffer from the nextprevious by a CH2 groupThey also form a homologous series


eg


Propene differ from ethene by one carbon and two Hydrogen atoms from ethene 4A homologous series of alkenes like that of alkanes


i differ by a CH2 group from the next previous consecutively


iihave similar chemical properties


iiihave similar chemical formula represented by the general formula CnH2n


ivthe physical properties also show steady gradual change


5The  C C  double bond in alkene is the functional group A functional group is the reacting site of a moleculecompound


6 The  C C  double bond in alkene can easily be broken to accommodate more two more monovalent atoms The  C C  double bond in alkenes make it thus unsaturated


7 An unsaturated hydrocarbon is one with a double CC or triple  C C  carbon bonds in their molecular structure Unsaturated hydrocarbon easily reacts to be saturated


8A saturated hydrocarbon is one without a double CC or triple  C C  carbon bonds in their molecular structure


Most of the reactions of alkenes take place at the  C  C bond


bIsomers of alkenes


Isomers are alkenes lie alkanes have the same molecular general formula but different molecular structural formula


Ethene and propene do not form isomers Isomers of alkenes are also named by using the IUPACInternational Union of Pure and Applied Chemistry system of nomenclaturenaming


The IUPAC system of nomenclature of naming alkenes uses the following basic rulesguidelines


1Identify the longest continuousstraight carbon chain which contains the C  C double bond getdetermine the parent alkene


2Number the longest chain form the end of the chain which contains the C  C double bond so he C  C double bond lowest number possible


3 Indicate the positions by splitting alkpositionsene eg but2ene pent13diene


4The position indicated must be for the carbon atom at the lower position in the C  C double bondie


But2ene means the double C  C is between Carbon 2and 3


Pent13diene means there are two double bond one between carbon 1 and 2and another between carbon 3 and 4


5 Determine the position number and type of branches Name them as methyl ethyl propyl etc according to the number of alkyl carbon chains attached to the alkene Name them fluorochlorobromoiodo if they are halogens


6Use prefix ditritetrapentahexa to show the number of double C  C bonds and branches attached to the alkene


7Position isomers can be formed when theC  C double bond is shifted between carbon atoms eg


But1ene means the double C  C is between Carbon 1and 2


Both But1ene and But2ene are position isomers of Butene


8Position isomers are moleculescompounds having the same general formular but different position of the functional groupie


Butene has the moleculargeneral formular C4H8 position but can form both But1ene and But2ene as position isomers


9 Like alkanes an alkyl group can be attached to the alkene Chainbranch isomers are thus formed


10Chainbranch isomers are moleculescompounds having the same general formula but different structural formula eg


Butene and 2methyl propene both have the same general formualr but different branching chain


Practice on IUPAC nomenclature of alkenes


Name the following isomers of alkene


H H H H


H C C C C H But1ene


H H


H C C C C H But2ene


H H H H H H


H C C C C C C H 4methylhex1ene


H H H


H C H


H


H H H H H


H C C C C C C H 44dimethylhex1ene


3 H


H C C C C C H 44dimethylpent 1 ene


4 H


H C C C C C H 55dimethylhex2 ene


H C H H H


5 H


H C C C C H 22dimethylbut 2 ene


8H2C CHCH2 CH2 CH3 pent 1 ene


9H2C CCH3CH2 CH2 CH3 2methylpent 1 ene


10H2C CCH3CCH32 CH2 CH3 233trimethylpent 1 ene


11H2C CCH3CCH32 CCH32 CH3 23344pentamethylpent 1 ene


12H3C CCH3CCH3 CCH32 CH3 2344tetramethylpent 2 ene


13 H2C CCH3CCH3 CCH3 CH3 234trimethylpent 13 diene


14 H2C CBrCBr CBr CH3 234tribromopent 13 diene


15 H2C CHCH CH2 But 13 diene


16 Br2C CBrCBr CBr2 112344hexabromobut 13 diene


17 I2C CICI CI2 112344hexaiodobut 13 diene


18 H2C CCH3CCH3 CH2 23dimethylbut 13 diene


cOccurrence and extraction


At indusrial levelalkenes are obtained from the cracking of alkanesCracking is the process of breaking long chain alkanes to smallershorter alkanes an alkene and hydrogen gas at high temperatures


Cracking is a major source of useful hydrogen gas for manufacture of ammonianitricVacidHCl ie


Long chain alkane  smallershorter alkane  Alkene  Hydrogen gas


Examples


1When irradiated with high energy radiationPropane undergo cracking to form methane gas ethene and hydrogen gas


Chemical equation


CH3CH2CH3 g  CH4g  CH2CH2g  H2g


2Octane undergo cracking to form hydrogen gas butene and butane gases


CH3CH2 6 CH3 g  CH3CH2CH2CH3g  CH3 CH2CHCH2g  H2g


dSchool laboratory preparation of alkenes


In a school laboratory alkenes may be prepared from dehydration of alkanols using


i concentrated sulphuricVIacidH2SO4


a aluminiumIIIoxideAl2O3 ie


Alkanol Conc H2SO4  Alkene  Water


Alkanol Al2O3  Alkene  Water eg


1aAt about 180oCconcentrated sulphuricVIacid dehydratesremoves water from ethanol to form ethene


The gas produced contain traces of carbonIVoxide and sulphurIVoxide gas as impurities


It is thus passed through concentrated sodiumpotassium hydroxide solution to remove the impurities


CH3CH2OH l conc H2SO4180oC CH2CH2g  H2Ol


bOn heating strongly aluminiumIIIoxideAl2O3it dehydratesremoves water from ethanol to form ethene


Ethanol vapour passes through the hot aluminium III oxide which catalyses the dehydration


Activated aluminiumIIIoxide has a very high affinity for water moleculeselements of water and thus dehydrates removes water from ethanol to form ethene


Chemical equation


CH3CH2OH l Al2O3strong heat CH2CH2g  H2Ol


2a Propan1ol and Propan2olposition isomers of propanol are dehydrated by conc H2SO4 at about 180oC to propenepropene has no position isomers


CH3CH2 CH2OH l  conc H2SO4180oC  CH3CH2CH2g  H2Ol


Propan1ol Prop1ene


CH3CHOH CH3 l  conc H2SO4180oC  CH3CH2CH2g  H2Ol


Propan2ol Prop1ene


b Propan1ol and Propan2olposition isomers of propanol are dehydrated by heating strongly aluminiumIIIoxideAl2O3 form propene


CH3CH2 CH2OH l  HeatAl2O3  CH3CH2CH2g  H2Ol


CH3CHOH CH3 l  HeatAl2O3  CH3CH2CH2g  H2Ol


3a Butan1ol and Butan2olposition isomers of butanol are dehydrated by conc H2SO4 at about 180oC to But1ene and But2ene respectively


CH3CH2 CH2 CH2OH l  conc H2SO4180oC CH3 CH2CH2CH2g  H2Ol


Butan1ol But1ene


CH3CHOH CH2CH3 l conc H2SO4180oC CH3CHCH CH2g  H2Ol


Butan2ol But2ene


b Butan1ol and Butan2ol are dehydrated by heating strongly aluminium III oxide Al2O3 form But1ene and But2ene respectively


CH3CH2 CH2 CH2OH l  HeatAl2O3  CH3 CH2CH2CH2g  H2Ol


CH3CHOH CH2CH3 l  HeatAl2O3  CH3CHCH CH2g  H2Ol


Laboratory set up for the preparation of alkenesethene


Caution


iEthanol is highly inflammable


iiConc H2SO4 is highly corrosive on skin contact


iiiCommon school thermometer has maximum calibration of 110oC and thus cannot be used It breakscracks


iUsing conentrated sulphuricVIacid


Some broken porcelain or sand should be put in the flask when heating to


iprevent bumping which may break the flask


iiensure uniform and smooth boiling of the mixture


The temperatures should be maintained at above160oC


At lower temperatures another compound ether is predominantly formed instead of ethene gas


iiUsing aluminiumIIIoxide


eProperties of alkenes


I Physical properties


Like alkanes alkenes are colourles gases solids and liquids that are not poisonous


They are slightly soluble in water


The solubility in water decrease as the carbon chain and as the molar mass increase but very soluble in organic solvents like tetrachloromethane and methylbenzene


The melting and boiling point increase as the carbon chain increase


This is because of the increase in vanderwaals intermolecular forces as the carbon chain increase


The 1st four straight chain alkenes ethenepropanebut1ene and pent1eneare gases at room temperature and pressure


The density of straight chain alkeneslike alkanes increase with increasing carbon chain as the intermolecular forces increases reducing the volume occupied by a given mass of the alkene


Summary of physical properties of the 1st five alkenes


II Chemical properties


aBurningcombustion


Alkenes burn with a yellow luminous sooty smoky flame in excess air to form carbonIV oxide and water


Alkene  Air  carbonIV oxide  water excess airoxygen


Alkenes burn with a yellow luminous sooty smoky flame in limited air to form carbonII oxide and water


Alkene  Air  carbonII oxide  water limited air


Burning of alkenes with a yellow luminous sooty smoky flame is a confirmatory test for the presence of the CC double bond because they have higher CH ratio


A homologous series with C  C double or C C triple bond is said to be unsaturated


A homologous series with C C single bond is said to be saturatedMost of the reactions of the unsaturated compound involve trying to be saturated to form a


C C single bond


Examples of burning alkenes


1a Ethene when ignited burns with a yellow sooty flame in excess air to form carbonIV oxide and water


Ethene  Air  carbonIV oxide  water excess airoxygen


C2H4g  3O2g  2CO2g  2H2Olg


b Ethene when ignited burns with a yellow sooty flame in limited air to form carbonII oxide and water


Ethene  Air  carbonII oxide  water limited air


2a Propene when ignited burns with a yellow sooty flame in excess air to form carbonIV oxide and water


Propene  Air  carbonIV oxide  water excess airoxygen


2C3H6g  9O2g  6CO2g  6H2Olg


a Propene when ignited burns with a yellow sooty flame in limited air to form carbonII oxide and water


C3H6g  3O2g  3COg  3H2Olg


bAddition reactions


An addition reaction is one which an unsaturated compound reacts to form a saturated compoundAddition reactions of alkenes are named from the reagent used to cause the addtionconvert the double CC to single CC bond


iHydrogenation


Hydrogenation is an addition reaction in which hydrogen in presence of PalladiumNickel catalyst at high temperatures react with alkenes to form alkanes


Examples


1When Hydrogen gas is passed through liquid vegetable and animal oil at about 180oC in presence of Nickel catalystsolid fat is formed


Hydrogenation is thus used to harden oils to solid fat especially margarine


During hydrogenation one hydrogen atom in the hydrogen molecule attach itself to one carbon and the other hydrogen to the second carbon breaking the double bond to single bond


Chemical equation


H2CCH2  H2 NiPa H3C  CH3


H H H H


C  C  H  H  NiPa  H  C  C  H


2Propene undergo hydrogenation to form Propane


H3C CHCH2  H2 NiPa H3C CH  CH3


H H H H H H


H C C  C  H  H  NiPa H  C  C  C H


H H H H H


3Both But1ene and But2ene undergo hydrogenation to form Butane


But1ene  Hydrogen NiPa Butane


H3C CH2 CHCH2  H2 NiPa H3C CH2CH  CH3


H H H H H H H H


H C C  C  C  H  H  NiPa H  C C  C  C H


H H H H H H H


But2ene  Hydrogen NiPa Butane


H3C CH2 CH CH2  H2 NiPa H3C CH2CH  CH3


H C C  C  C H  H  H  NiPa H  C C  C  C H


4 But13diene should undergo hydrogenation to form Butane The reaction uses two moles of hydrogen moleculesfour hydrogen atoms to break the two double bonds


But13diene  Hydrogen NiPa Butane


H2C CH CHCH2  2H2 NiPa H3C CH2CH  CH3


H C C  C  C H  2H  H  NiPa H  C C  C  C H


H H H H


ii Halogenation


Halogenation is an addition reaction in which a halogen Fluorine chlorine bromine iodine reacts with an alkene to form an alkane


The double bond in the alkene break and form a single bond


The colour of the halogen fades as the number of moles of the halogens remaining unreacted decreasesreduces


One bromine atom bond at the 1st carbon in the double bond while the other goes to the 2nd carbon


Examples


1Ethene reacts with bromine to form 12dibromoethane


Chemical equation


H2CCH2  Br2 H2 Br C  CH2 Br


C  C  Br  Br Br  C  C  Br


Ethene  Bromine 12dibromoethane


2Propene reacts with chlorine to form 12dichloropropane


H3C CHCH2  Cl2 H3C CHCl  CH2Cl


Propene  Chlorine 12dichloropropane


H H H H H H


H C C  C  Cl  Cl H  C  C  C Cl


H H H Cl H


H H H H H H H H


H C C  C  C  I  I H  C C  C  C I


3Both But1ene and But2ene undergo halogenation with iodine to form 12diiodobutane and 23diiodobutane


But1ene  iodine 12 diiodobutane


H3C CH2 CHCH2  I2 H3C CH2CH I  CH2I


But2ene  Iodine 23diiodobutane


H3C CH CHCH2  F2 H3C CHICHI  CH3


H C C  C  C H  I  I H  C C  C  C H


H H H I I H


4 But13diene should undergo halogenation to form Butane The reaction uses two moles of iodine moleculesfour iodine atoms to break the two double bonds


But13diene  iodine 1234tetraiodobutane


H2C CH CHCH2  2I2 H2CI CHICHI  CHI


H C C  C  C H  2I  I H  C C  C  C H


I I I I


iii Reaction with hydrogen halides


Hydrogen halides reacts with alkene to form a halogenoalkane The double bond in the alkene break and form a single bond


The main compound is one which the hydrogen atom bond at the carbon with more hydrogen


Examples


1 Ethene reacts with hydrogen bromide to form bromoethane


Chemical equation


H2CCH2  HBr H3 C  CH2 Br


H H H H


C  C  H  Br H  C  C  Br


Ethene  Bromine bromoethane


2 Propene reacts with hydrogen iodide to form 2iodopropane


H3C CHCH2  HI H3C CHI  CH3


Propene  Chlorine 2chloropropane


H H H H H H


H C C  C  H  Cl H  C  C  C H


H H H Cl H


3 Both But1ene and But2ene reacts with hydrogen bromide to form 2 bromobutane


But1ene  hydrogen bromide 2bromobutane


H3C CH2 CHCH2  HBr H3C CH2CHBr CH3


H H H H H H H H


H C C  C  C  H  Br H  C C  C  C H


H H H H H Br H


But2ene  Hydrogen bromide 2bromobutane


H3C CH CHCH2  HBr H3C CHBrCH2  CH3


H C C  C  C H  Br  H H  C C  C  C H


H H H Br H H


4 But13diene react with hydrogen iodide to form 23 diiodobutane The reaction uses two moles of hydrogen iodide moleculestwo iodine atoms and two hydrogen atoms to break the two double bonds


But13diene  iodine 23diiodobutane


H2C CH CHCH2  2HI2 H3CCHICHI  CH3


H C C  C  C H  2H  I H  C C  C  C H


H I I H


iv Reaction with brominechlorine water


Chlorine and bromine water is formed when the halogen is dissolved in distilled waterChlorine water has the formular HOClhypochlorouschloricIacid Bromine water has the formular HOBrhydrobromicIacid


During the addition reaction the halogen move to one carbon and the OH to the other carbon in the alkene at the CC double bond to form a halogenoalkanol


Bromine water  Alkene  bromoalkanol


Chlorine water  Alkene  bromoalkanol


Examples


1Ethene reacts with bromine water to form bromoethanol


Chemical equation


H2CCH2  HOBr H2 Br C  CH2 OH


H H H H


C  C  Br  OH Br  C  C  OH


Ethene  Bromine water bromoethanol


2Propene reacts with chlorine water to form chloropropan2ol  2chloropropan1ol


IH3C CHCH2  HOCl H3C CHCl  CH2OH


Propene  Chlorine water 2chloropropane


H H H H H H


H C C  C  HO  Cl H  C  C  C OH


H H H Cl H


IIH3C CHCH2  HOCl H3C CHOH  CH2Cl


Propene  Chlorine chloropropan2ol


H C C  C  HO  Cl H  C  C  C Cl


H H H OH H


3Both But1ene and But2ene react with bromine water to form 2bromobutan1ol 3bromobutan2ol respectively


IBut1ene  bromine water 2bromobutan1ol


H3C CH2 CHCH2  HOBr H3C CH2CH Br  CH2OH


H H H H H H H H


H C C  C  C  HO Br H  C C  C  C OH


H H H H H Br H


IIBut2ene  bromine water 3bromobutan2ol


H3C CH CHCH3  HOBr H3C CH2OHCH Br CH3


4 But13diene reacts with bromine water to form Butan13diol


The reaction uses two moles of bromine water molecules to break the two double bonds


But13diene  bromine water 24dibromobutan13diol


H2C CH CHCH2  2HOBr H2COH CHBrCHOH CHBr


H C C  C  C H  2HO  Br H  C C  C  C H


HO Br HO Br


v Oxidation


Alkenes are oxidized to alkanols with duodouble functional groups by oxidizing agents


When an alkene is bubbled into orange acidified potassiumsodium dichromate VI solutionthe colour of the oxidizing agent changes to green


When an alkene is bubbled into purple acidified potassiumsodium manganateVII solution the oxidizing agent is decolorized


Examples


1Ethene is oxidized to ethan12diol by acidified potassiumsodium manganateVII solution acidified potassiumsodium dichromateVI solution


The purple acidified potassiumsodium manganateVII solution is decolorized


The orange acidified potassiumsodium dichromateVI solution turns to green


Chemical equation


H2CCH2 O in HK2Cr2O7 HO CH2  CH2 OH


H H H H


C  C O in HKMnO4 H  C  C  H


H H OH OH


Ethene  O in HKMnO4 ethan12diol


2 Propene is oxidized to propan12diol by acidified potassiumsodium manganateVII solution acidified potassiumsodium dichromateVI solution


H3C CHCH2 O in HKMnO4 H3C CHOH  CH2OH


Propene O in HKMnO4 propan12diol


H H H H H H


H C C  C O in HKMnO4 H  C  C  C OH


H H H OH H


3Both But1ene and But2ene react with bromine water to form butan12diol and butan23diol


IBut1ene  O in HKMnO4 butan12diol


H3C CH2 CHCH2  O H3C CH2CHOH  CH2OH


H H H H H H H H


H C C  C  C  O H  C C  C  C OH


H H H H H OH H


v Hydrolysis


Hydrolysis is the reaction of a compound with wateraddition of HOH to a compound


Alkenes undergo hydrolysis to form alkanols


This takes place in two steps


iAlkenes react with concentrated sulphuricVIacid at room temperature and pressure to form alkylhydrogen sulphateVI


Alkenes  concentrated sulphuricVIacid  alkylhydrogen sulphateVI


iiOn adding water to alkylhydrogen sulphateVI then warming an alkanol is formed


alkylhydrogen sulphateVI  water warm Alkanol


Examples


iEthene reacts with cold concentrated sulphuricVIacid to form ethyl hydrogen sulphateVII


Chemical equation


H2CCH2  H2SO4 CH3  CH2OSO3H


H H H OSO3H


C  C  H2SO4 H  C  C  H


H H H H


Ethene  H2SO4 ethylhydrogen sulphateVI


ii Ethylhydrogen sulphateVI is hydrolysed by water to ethanol


CH3  CH2OSO3H  H2O CH3  CH2OH  H2SO4


H OSO3H H OH


H  C  C  H  H2O H  C  C  H  H2SO4


ethylhydrogen sulphateVI  H2O Ethanol


2 Propene reacts with cold concentrated sulphuricVIacid to form propyl hydrogen sulphateVII


CH3H2CCH2  H2SO4 CH3CH2  CH2OSO3H


H H H H H OSO3H


C  C  C  H  H2SO4 H  C  C  C  H


H H H H H H


Propene  H2SO4 propylhydrogen sulphateVI


ii Propylhydrogen sulphateVI is hydrolysed by water to propanol


Chemical equation


H H OSO3H H H OH


H  C  C  C  H  H2O H  C  C  C  H  H2SO4


propylhydrogen sulphateVI  H2O propanol


vi Polymerizationself addition


Addition polymerization is the process where a small unsaturated monomer alkene  molecule join together to form a large saturated molecule


Only alkenes undergo addition polymerization