Chemistry - Unit2

Thermodynamics Study of conversion of energy between heat and other forms Thermochemistry Relationship between chemical reactions and heat changes Enthalpy H Measure of energy(heat content) Change Final value minus the initial value  –1 Enthalpy change H kJmol Heat energy transferred in a reaction at constant pressure H = (H)Products - (H)Reactants Heat changes depend on conditions in which they are measured(open containers/atmospheric/consta containers/atmospheric/constant nt pressure) θ Standard conditions H 298K 100kPa Internationally Internationally agreed conditions under which a standard ∆ H should be measured Endothermic reactions Heat absorbed, products have more enthalpy than reactants, decrease in temp of surroundings(photosynthesis) Exothermic reactions Heat evolved, products have less enthalpy than reactants, increase in temp of surroundings (oxidation H+(aq) + OH – (aq)  H2O(l)) − Change in physical state is accompanied by ∆ H Allotrope A structurally different form of an element in the same physical state caused by the possibility of more than one arrangement of  atoms(graphite and diamond are allotropes of carbon) G ‘free energy’ difference between the products and reactants when 1 mole of a substance is completely completely burned in O2(excess Standard enthalpy of combustion Hc θ(exothermic) Enthalpy change when air), at 298K 100kPa − Combustion won’t take place under standard conditions but measurement of ∆ H must be made when the conditions at the start and end of the reaction are standard − Energy value of fuel/food based on ∆ Hc since combustion and processes that fuel/food undergoes in the body gives rise to the same  product. 1 cal = 4.18J, calorific values of food important for people controlling their energy energy intake for dietary reasons Standard state of an element The most stable form of the element under standard conditions H2(g), O2(g), Cu(s) Standard enthalpy of formation Hf  θ Enthalpy change when one mole of a compound is formed from its elements, at 298K 100kPa ∆ Hf  of any element in its standard state is zero Enthalpy of neutralisation HN(exothermic) Enthalpy change when one mole of water is formed from a reaction of an acid with a base ∆ Hc of graphite is the same as ∆ Hf  of CO2 C(s, graphite) + O 2(g)  CO2(g) ∆ H θ = −393kJmol  –1 C(s, diamond) + O 2(g)  CO2(g) ∆ H θ = −395kJmol  –1 ∆ Hc of diamond but not ∆ Hf  of CO2 since carbon is not in its standard state Graphite is the standard state for carbon(it’s more thermodynamically thermodynamically stable at 298K) 2Li(s) + ½O2(g)  Li2O(s) ∆ Hf  of Li2O is not the ∆ Hc of lithium since 2 moles of lithium are involved in the equation

Enthalpy of fusion of H 2O Enthalpy of vapourisation of H2O

∆ H for the process H2O(s)  H2O(l) ∆ H for the process H2O(l)  H2O(g)

1°C ≡ 1K  Heat transfer(J) = m(g) x c x T Specific heat capacity (c) (Jg –1 °C –1) Amount of heat required to raise the temperature of 1g of substance by 1K  Temperature Measurement of KE of particles(independent of the amount) Heat Measurement of total energy in a substance(dependent on the amount) Calorimetry Measurement of heat transferred to known mass of another substance and measuring temp rise Calorimeter Apparatus used to measure heat given off in a chemical reaction Why ∆ T may not be accurate: accurate: • Loss of substance(ethanol) substance(ethanol) by evaporation • Heat transferred to calorimeter/lost calorimeter/lost to surroundings instead of the water(avoided by calibrating apparatus appropriately) appropriately) • Incomplete combustion combustion due to inadequate inadequate supply of of O2 leading to CO or C(indicated by deposit of soot on the bottom of calorimeter) 1st law of thermodynamics Energy can’t be created or destroyed, only converted from one form to another  Hess’s law ∆ H for a reaction is independent of the route it takes provided that the temperatures, pressures and physical states of the reactants and products are the same − ∆ H of reverse reaction is the same but with opposite sign

experimentally, if statements weren’t true − Hess’s law allows for calculation of enthalpy changes for reactions which can’t be measured experimentally, it’d be possible to create energy without any consumption of material

• • • • • • •

150g 23°C water in a glass beaker and stirred • After certain certain time time final temp noted Spirit burner reweighed • ∆ m of spirit burner gives mass of ethanol burned (0.9g) Heat gained by water in calorimeter calorimeter = mxcx∆ T = 150g x 4.2Jg –1 °C –1 x 20°C = 12600J Heat produced by burning 0.9g of ethanol ethanol = 12.6kJ  –1 Mr(C2H5OH) = 46gmol Ethanol used = 0.9g/46gmol  –1 = 0.01956mols So heat produced by burning burning 1 mol of ethanol = 12.6 x 1/0.01956 = 644kJ  –1 ∆ Hc = −640kJmol

• Note temp, 50cm3 1moldm –3 HCl in insulated polystyrene cup(beaker from expanded polystyrene) • Add 50cm3 1.1moldm –3 NaOH(excess NaOH(excess to ensure complete reaction)which is at same temp • Stir continuously continuously and note max max temp reached reached HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) Assuming no heat losses to surroundings and c of solution is 4.2Jg  –1 °C  –1 Heat absorbed by solution = m x c x ∆ T = 100g x 4.2Jg  –1 °C  –1 x 6.5°C = 2730J Acid= Acid= 0.05mol, 0.05mol, Heat given given by 1 mol mol of acid acid = 2730J/0.05m 2730J/0.05mol ol = 54.6kJmo 54.6kJmoll  –1 ∆ H N = −55kJmol  –1 − Heat loss to surroundings increases with slower reactions as heat lost over a longer period − The greater the heat loss to the surroundings the greater the correction of the temperature and the steeper the line • 1st reagent placed in polystyrene cup, temperature noted at 1min intervals for 4min stirring continuously • 2nd reagent added, temperature noted more frequently until max reached • As solution starts to to cool, temperature recording recording and stirring continued for 5min • Check that sign of ∆ H is correct • If equation is multiplied, also also multiply ∆ H value • ∆ Hf  of elements is 0 Conversion of graphite to requires high temperatures and pressures as huge amount of  energy is needed to disrupt bonds before atoms can  be rearranged into the diamond structure(with structure(with release of all but 2kJmol  –1 of the energy put in) (1)Calculate ∆ H for N2O4(g)  2NO2(g) 2NO2(g)  2NO(g) + O2(g) ∆ H θ = +109kJmol  –1 ½N2(g) + ½O2(g)  NO(g) ∆ H θ = +90kJmol  –1  N2(g) + 2O2(g)  N2O4(g) ∆ H θ = +8kJmol  –1

(1) H = [sum of  H f  products] [sum of  H θf  reactants] (2)∆ H θc(NH3)? ∆ H θf  NH  NH3(g)= −46.1kJmol  –1 ∆ H θf H2O(g)= −242kJmol θ

 –1

(2) 4NH3(g) + 3O2(g)  2N2(g) + 6H2O(g) {6x(−242) + 2x0} − {4x(−46) + 3 x0} = −1268kJmol  –1 ∆ H θc(NH3) = −1268/4 = -317 kJmol  –1 (1)(a)Find ∆ Hf  θ(CO)using a Hess’s law cycle, C(graphite) + ½O2(g) → CO(g)

(C(graphite))= –394 kJmol kJmol –1 ∆  H cθ(C(graphite))= e .g . C

(∆ H

c om b

+

1/ 2

C a rb o n )

O

2

C O

(∆ H (∆ H

c om b

form

∆  H cθ(CO(g))= –283 kJmol –1 C O )

C a r b o n m o n o x id e )

C O 2 (1 ) (a) = −394 −(−283) = −111kJmol –1 (b)Suggest why it’s not possible to find ∆ Hf (CO) directly (b)(some)CO2 is always produced in the reaction

Enthalpy of dissociation Enthalpy change when 1 mole of a gaseous substance is broken up into free gaseous atoms (measure of strength of covalent bonds) − Bond breaking is endothermic, need energy to break bonds Bond forming is exothermic, energy energy released when bonds are formed θ  –1 1664/4 = 416kJmol  –1 − Average bond enthalpy CH4(g)C(g) + 4H(g) ∆ H = +1664kJmol (specific bond enthalpies for the 4C −H bonds are different)

H = [sum of average bond enthalpies of reactants]

[ sum of average bond enthalpies of products]

(1)Calculate ∆ Hf (H (H2O) H2(g) + ½O2(g)H2O(l) E(H−H)(g) = 436kJmol  –1; E(O=O)(g) = 49 498kJmol  –1; E(O−H)(g) = 464kJmol –1 (a)∆ H = [E(H−H) + ½E(O=O)] −[2E(O−H)] = [436 + 249] − 928 = −243kJmol  –1 ∆ H for H2O(g)  H2O(l); ∆ H = −44 −44kJmol  –1; −243 + (−44) = −287kJmol –1 (b)Suggest why the value obtained in (a)may not be accurate (b)Average values used in bond enthalpies (2)When hydrogen reacts with chlorine in a container of fixed volume the pressure increases but the number of molecules has not changed. What is the sign of ∆ H? (2)H2(g) + Cl2(g)  2HCl(g) As the number of molecules doesn’t change during the reaction, the only reason for an increase in pressure can be an increase in temperature. temperature. This means that the reaction reaction is exothermic and ∆ H is negative (3)Is ∆ Hc(H2) same as ∆ Hf  (H2O)? (3)Yes, provided the conditions are the same H2(g) + ½O2(g)  H2O(l) (4)Is ∆ Hc(CO) the same as ∆ Hf (CO (CO2)? (4)Ent (4)Enthal halpy py chan changes ges are are not not the the same same even even thou though gh they they both both produc producee 1 mole mole of CO2 θ (5)Define ∆ Hf  (urea) (5) • Enthalpy change for the formation of 1 mol of urea, from its elements, in their standard states/100kPa states/100kPa 298K  (6)(a) Find ∆ H for: 2C(graphite) + 2H2(g) + O2(g) → CH3COOH(l) (C(graphite))= –394kJmol –1 ∆ Hc(C(graphite))=

∆ Hc(H2(g))= –286kJmol –1

COOH(l))= –874kJmol –1 ∆ Hc(CH3COOH(l))=

(a)∆  H =  H = [2(∆  H c(C)) + 2(∆  H c(H2))] − [∆  H c(CH3COOH)] = −486 kJ mol –1

(b)What is the ∆ H obtained in (a) called? (b) ∆ Hf 

30 29 T e m p e r a tu r e / ºC 28 27 26 25 24 23 22 21 20 0

4

8

12

16

20

24 28 32 36 V o lu m e o f N a O H (a q ) / c m

40  – 3

(7)(a) 20cm3 1moldm –3copper salt(aq) in a polystyrene polystyrene cup. Burette filled filled with 2moldm –3 NaOH(aq) 2cm3 NaOH(aq) was run into the copper salt(aq) and temp measured measured immediately. As soon as possible a further 2cm3 of NaOH(aq) was run in and temp measured again, process continued until 36cm3 of NaOH(aq) had been added (i)Explain why the temp reaches a max and then falls slightly on addition of further NaOH(aq) (i)Reaction is complete, addition of cooler NaOH causes temp to fall (ii)Calculate (ii)Calculate the amount of copper ions that have reacted (ii)20× 1/1000 =0.02mol (iii)Write (iii)Write the formula of the copper hydroxide that is produced (iii)Cu(OH) (iii)Cu(OH) 2 (b)Identify a source of error in this experiment, and say what you would do to reduce its effect (b) • Poor mixing, use(magnetic use(magnetic stirrer/swirl cup)between cup)between additions, to ensure even temp/reaction faster so less heat loss with time • Solutions at different different initial temperatures, allow them to stabilise stabilise at RT • Measure temperature temperature more often. Allows for for more accurate accurate ∆ Τ from graph (8)A student calculates ∆ Hcθ (C2H5OH) = 853.54966 kJ mol –1 Give 3 criticisms of the value giving reasons (8) • Shown as standard value. value. Experiment not conducted conducted under ‘standard’ conditions conditions • Too many d.ps/signi d.ps/significa ficant nt figure figures. s. Accuracy Accuracy of appara apparatus tus doesn doesn’t ’t warra warrant nt • Not shown as negati negative. ve. Exothermi Exothermicc reacti reaction on

Organic chemistry The study of the chemistry of carbon compounds compounds with • similar chemical chemical properties properties • same functional groups • a general formula formula where Homologous series A set of compounds successive members differ by CH2 Structural formula How the various atoms are bonded to one another within the molecule - Factors affecting reactivity in organic compounds • single or double bonds • bond polarity • bond enthalpy - Larger alkanes release release a lot more energy per mole because because they have more bonds to react react - Carbon can catenate(form catenate(form stable covalent bonds with with itself) - Organic compounds thermodynamically thermodynamically unstable in the presence of oxygen oxygen CH4(l) + 2O2(g) CO2(g) + 2H2O(g) (-)∆ H But activation energies of the reactions with oxygen are high so organic compounds are kinetically stable at temperatures on earth If alkane and oxygen mixed first explosion will result on ignition Carbon 2s 2p Carbon 2s 2p  ground state excited   state - If one electron is promoted from the 2s orbital to the 2p orbital, 4 unpaired electrons become available - Energy to do this is more than compensated for by the energy released in the formation of 4 bonds instead of 2 - Electrons not all equal since they are in different types types of orbital(s & p, methane has 3 bonds of different length from the other one, so electrons are hybridised) Isomer Same molecular formula, different structural formulae

Structural isomerism Occurs when 2 or more different structural formulae can be written for the same molecular formula Chain isomers Different arrangements of carbon skeleton Similar chemical properties, differ in physical properties(Mt)because of change in shape of molecule

 Positional isomers Same skeleton and functional group, side chains/functional groups are in different positions on the carbon chain Differ in physical properties

 Functional group isomers Same atoms arranged into different functional groups Differ in physical & chemical chemical properties properties

Evidence that the 2 bonds in the C=C double bond are not the same: • Bond energy energy of C=C (612kJmol  –1) is greater than C-C (348kJmol  –1) but not as twice as big hence pi bond is weaker than the sigma  bond • Grea Greate terr str stren engt gth h of C=C C=C bon bond d sup suppo port rted ed by shor shorte terr bond bond leng length th(h (hen ence ce gre great ater er over overla lap) p) • Exis Existe tenc ncee of geom geomet etri ricc iso isome mers rs Stereoisomerism Molecules have same molecular formula, same structural Stereoisomerism Stereoisomerism found in any molecule of the type: formula, but atoms have a different 3d arrangement(orientation arrangement(orientation in space). Differ in physical properties Geometric Isomerism Occurs when there’s restricted rotation about a bond(C=C double bond where each of the two C atoms carries 2 different atoms/groups)differ in physical properties(different positions of groups, chains affects shape, dipoles, intermolecular forces) Single sigma bond  Free rotation about this bond without any reduction in degree of overlap  Double bond  Restricted rotation about C=C double bond because rotation would lead to a decrease in overlap of p orbitals that give the  pi bond. Requires energy energy to break the bond and doesn’t happen at RT. RT. Heating geometric geometric isomers may cause their their interconversion.

Nucleophiles Species which seek out + centres. A molecule, atom or ion which can donate a lone pair of electrons to form a new dative covalent bond Electrophiles Species which seek out – centres. An electron deficient molecule, atom or ion, capable of accepting a lone pair of electrons to form a new dative covalent bond  Aromatic compounds Always contain rings, don’t show the properties expected of compounds with double bonds(benzene)  Aliphatic compounds Don’t contain rings, contain double bonds and show the expected reactions eg alkenes Alkanes CnH2n+2 Simplest homologous series, saturated hydrocarbons (every C atom has 4 single bonds with other atoms and it’s impossible for carbon to make more than 4 bonds hence alkanes are saturated) n Formula Name Bt °C Mt °C Colourless gases Methane used in homes for cooking, heating 1 CH4 Methane -162 -182 2 C2H6 Ethane -89 -183 Propane/butane, mobile sources of heat/light 3 C3H8 Propane -42 -188 for camping 4 C4H10 Butane -0.5 -138

5 6 7 8 9 10

C5H12 C6H14 C7H16 C8H18 C9H20 C10H22

Pentane Hexane Heptane Octane  Nonane Decane

36 69 98 126

-130 -95 -91 -57

C5 – C15 colourless liquids, liquid alkanes used in petrol for cars C15 + white waxy solids - Main sources of alkanes from crude oil, natural gas - Organic materials manufactured manufactured from alkanes, detergents, plastics, plastics, synthetic fibres - Inorganic materials manufactured manufactured from alkanes, hydrogen from processed processed alkanes is used to make ammonia

Mt of alkanes depends on size & shape: • Alkanes have covalent bonds within molecules molecules and intermolecular van der waals forces • A branched chain alkane has a lower Mt than straight chain isomer as branched chain alkanes can’t pack as closely together and have smaller molecular surface surface areas so van der waals forces are reduced. Therefore Mt decreases as branching increases increases - Fractional distillation distillation of crude oil: Separation of mixture mixture of alkanes and hydrocarbons hydrocarbons into groups of compounds with similar similar Bts Alkyl groups-C groups-CnH2n + 1 Not capable of independent existence but occurs within other molecules, CH 3 methyl group, CH2CH3 ethyl group - Names based on longest continuous C chain  Nomenclature A systematic way of naming chemical compounds Alkyl group names come before name of longest C chain preceded, by a number to indicate C atom at which substitution occurred Structural Isomerism In alkanes, only way in which different structures can be obtained is by rearranging the C chain • Straight chain isomer C atoms joined joined together in a continuous chain(bending chain doesn’t change length of C chain) • Branched chain isomer isomer C atoms form ‘side chains’ chains’ which can’t be of greater greater length than main chain 3 structural structural isomer of C5H12 CH3CH2CH2CH2CH3 CH3 CH3 | | 2,2-dimethylpropane Bt10°C Pentane Bt36°C CH3CH2CHCH3 CH3CCH3 CH3C(CH3)3 CH3(CH2)3CH3 2-methylbutane Bt28°C | CH3CH2CH(CH3)2 CH3 • Alkanes non-polar, not reacting reacting with polar chemicals(doesn’t dissolve in water) water) • Alkanes react with with non-polar substances given enough enough energy • Greenhouse effect(Increases effec t(Increases greenhouse greenhou se gases(CO2))which absorb IR radiation and stop Earth’s IR radiation getting out) Burning fuels earth warms up slowly, climate changes, polar ice caps melt leading to flooding. Control global warming by using cars less, replacing fossil fuels with other sources of energy (natural energy, wind, water) • Power stations add sulphur oxides to the air(scrubbers air(scrubbers reduce emissions)which are poisonous causing problems problems for people with asthma, causes acid rain which kills trees, damages buildings, makes lakes acidic killing aquatic life • Incomplete combustion(insuff combustion(insufficient icient O2 supply)produces supply)produces poisonous gas CO, vehicle engines make nitrogen oxides which add to acid rain problem, fuel which comes out without burning (unburned hydrocarbons) escape into the air as pollutants Renewable biofuels From plants, produce CO 2 when burned but plants take in CO2 so if replaced, won’t add to CO2 in the atmosphere. • Biodiesel made from from rapeseed oil, used in vehicles vehicles • Ethanol made by fermenting fermenting sugar cane, mixed mixed with petrol, fuel used in vehicles vehicles Cyclic alkanes Bond angles for smaller rings are different from 109° of the sp 3 CH2 CH2 – CH2 CH2 hybrid orbitals indicating poor overlap of the orbitals and considerable strain on / \ | | / \ the ring. CH2 – CH2 CH2 – CH2 CH2 CH2 - They behave as normal alkanes alkanes concerning the C-H bond but are are more reactive Cyclopropane Cyclobutane | | towards reagents which break the C-C bond CH2 CH2 \ / CH2 Cyclohexane

Halogenation Halogen atom replaces 1 or more of the H atoms in an alkane by a substitution reaction (atom/group of atoms in a molecule replaced by another atom/group of atoms) - ALL halogens react with ALL alkanes, alkanes, rate of reaction quicker with Cl than with Br than with I, I reaction results in equilibrium equilibrium - Rate of reaction decreases decreases as the relative molecular molecular mass of the alkane increases increases Free radical substitution reaction substitution involving a free radical(species which have a single unpaired electron, highly reactive) Photochemical reaction Reaction initiated by light, Sunlight(UV)light energy essential for reactions to proceed at a reasonable rate UV C6H14 + Br2 C6H13Br + HBr(steamy acidic fumes) Rapid decolourisation of bromine, if covered in a darkened test tube the colour remains longer  - All C-H bonds equivalent so no way of determining which H atom will be replaced replaced  Initiation reactions Free radicals produced Photo dissociation Cl22Cl•  Homolytic bond fission (Cova (Covalen lent)b t)bond ond splits splits equall equally y to to give give 2 free free radic radicals als X:Y  X• + Y•  Heterolytic bond fission Bond splits unequally and both electrons kept by one atom  Bond fission Bond breaking  Lysis Breakdown  Homo Same  Hetero Different  Heterolytic Bond cleavage where + & – ions produced  Homolytic Bond cleavage where 2 neutral species produced  Propagation reactions Free radicals used up and created in chain reaction Cl• + CH4  CH3• + HCl CH3• + Cl2  CH3Cl + Cl• etc until no more Cl2 / CH4 molecules Termination reactions Free radicals mopped up 2 free radicals join together making a stable molecule, some products forming trace impurities in final sample Lots ots of of poss possiible ble ter term mina inatio tion re reacti actio ons Cl• + Cl• Cl•  Cl2 or Cl• + CH3•  CH3Cl or CH3• + CH3•  CH3Cl + C2H6  More substitutions Dependent on amount of excess chlorine or methane Excess Excess chlorine chlorine Cl• free radical radicalss start attacking attacking chlorometh chloromethane ane giving giving dichlorometh dichloromethane ane CH2Cl2 trichloromethane trichloromethane CHCl3 tetrachloromethane tetrachloromethane CCl4 Excess Excess methane methane Product Product will will be mostly mostly chlor chlorometh omethane ane Alkenes CnH2n Unsaturated molecules because of C=C double bond - Alkenes have lower Mt because less H atoms, so lower van der waals forces but more reactive because of C=C double bond Structural Isomerism Occurs by moving the double bond to different positions in the C chain indicated by the number between the  prefix & -ene, number being the smallest possible counting from each end which takes precedence in numbering of the C atoms of the longest C chain(isomer 3-methylbut-1-ene is not 2-methylbut-3-ene) - 3 possibilities possibilities of C4H8 but-1-ene CH3CH2CH=CH2 (-cis or -trans)but-2-eneCH -trans)but-2-eneCH3CH=CHCH3 Addition reaction 2 molecules react together forming a single product H H H H Electrophilic addition Addition reaction where, electrophile attacks a molecule at a region of high | | RT | | electron density –C=C –C=C– – + A–B A–B  –C–C–  - Electophilic addition addition reaction of alkenes at high electron density(pi bond, double bond is nucleophilic) | |  pi bond breaks, bonds formed with reactant molecule A B Tests for unsaturation C=C bond Pure bromine a safety hazard, avoided by dissolving it in an organic solvent(hexane) RT, shake(as hydrocarbons are immiscible with water) CH3CH=CHCH3 + Br2(aq) CH3CHBrCHBrCH3 decolourised But-2-ene 2,3-dibromobutane(dibromoalkane) CH2=CH2 + H2O + [O] HOCH2CH2OH [O] oxygen from the oxidising agent Ethene ethane-1,2-diol Oxidation of alkenes by purple by purple alkaline KMnO4 (potassium manganate(VII manganate(VII)) )) (warning, other reducing agents give positive results)  –   –  2–  • CH2=CH2 + 2MnO4 + 2OH HOCH2CH2OH + 2MnO4 Manganate ions first reduced to green manganate ions, green solution • 3CH2=CH2 + 2MnO4 – + 4H2O HOCH2CH2OH + 2MnO2 + 2OH –  (neutral or acidic conditions, no OH – /H+on LHS) then to dark brown ppt manganese dioxide Oxidation of alkenes by acidic purple KMnO4 turns colourless colourless,, manganate(VII) ions reduced to manganese(II) ions 5CH2=CH2 + 2H2O + 2MnO4 –  + 6H+ 5HOCH2CH2OH+ 2Mn2+

Alkene with H2 Addition, reduction reaction - Cheaper nickel catalyst catalyst used to convert unsaturated unsaturated oils into saturated saturated fats for use in margarine

Finely divided nickel/platinum catalyst H H 150°C H H \ / High Pressure | | C=C + H2(g)  H–C–C–H / \ | | H H H H Ethene(Alkene) Ethane(Alkane)

RT Electrophilic addition H2C=CH2 + HBr(not aq) CH3CH2Br Ethane Bromoethane(Bromoalkane colourless liquid) H2C=CHCH2CH3 + HBr 2 products BrCH2CH2CH2CH3 1-bromobutane CH3CHBrCH2CH3 2-bromobutane Major product because more stable with more attached alkyl groups Alkenes with H2SO4(catalyst) Electrophilic addition, hydrolysis cold conc H2SO4 H2C=CH2 CH3CH2OH Alkene with H2O(g) Reaction yield low 5%, recycle unreacted gas to get yield 95% 300°C 60atm H3PO4(s) Phosphoric(V) acid catalyst H2C=CH2(g) + H2O(g) CH3CH2OH(g) Poly(ethe Poly(eth ene)‘polythene’ ne)‘pol ythene’ LDPE(Low Density Density Polythene) Polythene) Polymer chains very branched, branched, not packing Addition polymerisation, electrophilic addition reaction closely, amorphous(non crystalline) crystalline) • Strong • Flexible • Deformed by heat (H2C=CH2)n (–CH2 –CH  –CH2 –)n packaging, electrical insulation insulation Monomer ethene(repeating unit, essentially an alkane) - Used in bags, bottles, packaging, - LDPE made by ethene at 2000atm 500K  HDPE(High HDPE(High Density Polythene) Polythene) Polymer chains branched branched little, chains line up  Ziegler Natta catalysts are mixtures of titanium  packing closely, crystalline structure compounds like titanium(III)chloride TiCl 3 or  • Strong • Rigid • Not deformed by heat • Easy to mould titanium(IV)chloride titanium(IV)chloride TiCl 4 and compounds of  - Used in water pipes, petrol petrol tanks, containers, hospital hospital equipment needing aluminium like aluminium triethyl Al(C 2 H   H 5 )  )3 sterilising - HDPE made made by ethene ethene at 25atm 330K Ziegler Natta catalyst - Polymerisation Polymerisation of propene produces stereoregular polymers, polymers, regular geometrical Poly(propene) H CH3 Ziegler Natta H CH3 arrangement of methyl groups in a spiral which stiffens the structure allowing the long | | | | molecules to line up close to one another, increasing Hardness • Wear-resistance, Wear-resistance, strength strength of the the material material • Softening temp ( C=C )n ( –C–C– )n • Hardness - Longer chains means greater van der waals forces which get tangled so less flexibility flexibility | | | | - Used to make ropes, sacking, sacking, carpets, fishing net netss H H H H Alkene with HBr

Poly(chloroethene) PVC H Cl H Cl - Amorphous, large chlorines stick stick out randomly from the chains so they don’t pack closely | | | | - PVC unusually hard & rigid because C–Cl bonds are polarised(Cl polarised(Cl more EN than C)dipole-dipole ( C=C )n ( –C–C– )n int interac eracti tion onss exi exisst bet betw ween een cha chain inss To mak makee PV PVC mor moree fle flexi xibl ble, e, pla plasti sticise ciserrs are are adde added d | | | | To make PVC more hard, mineral fillers are added H H H H - Used for water pipes(rigidity, pipes(rigidity, resistance to wear), rainwear, rainwear, coating on electric cables(at high temps can Chloroethene PVC melt causing short circuits and give toxic chlorine containing compounds) Poly(fluoroethene)PTFE or Teflon - Solid is • Hard, strong • Slippery • High Mt F F F F - PTFE inert because because • C–F bond is strong strong • Resistant to hydrolysis hydrolysis | | | | • Big F atoms protect protect C chain from chemical chemical attack  ( C=C )n ( –C–C– )n - PTFE has high electron electron density due to F atoms atoms and close packing, | | | | Vdw forces stronger than HDPE F F F F - Used in surface coating for non-stick ovenware, low friction friction bearings, seals, pipes, skis, Tetraflu Tetrafluroet roethene hene Poly(tet Poly(tetrafl rafluroe uroethene thene)) stain–proofing of fabrics - Polymers cause environmental environmental problems when disposed, when burned, give off toxic fumes, not biodegradable biodegradable so would accumulate in rubbish tips never to disappear  - Polymers can be recycled(but recycled(but expensive to sort out plastics)break waste polymers polymers into smaller molecules by cracking, use the small molecules as raw materials for making new polymers or other chemicals

Ideal fuel should 1 Be abundant  Methane, butane, octane, coal, finite finite resources. Ethanol replaceable replaceable by fermentation of sugars of  vegetable origin, however if earth’s energy needs were to be met by ethanol it is debatable whether enough vegetable matter could be  produced. Hydrogen obtained by electrolysis of water, burning it converts it back to its source, regenerated by electrolysis where oxygen used to  burn it is recovered. But fuel required to produce energy, and more than all the energy is used to recover the fuel reaction) Transport of liquid fue fuell is dangerous but gases more so. 2 Be easy & safe safe to store & move move (high EACT for combustion reaction) - Liquid fuels are easy to store/transport store/transport whereas gases will need to be stored under pressure in a special container as a liquid/in a large container as a gas Hydrogen is difficult, a highly flammable gas, can’t be liquefied under pressure at RT, the more stored the higher the pressure, the stronger and heavier the container must be, so storage & transport of hydrogen is dangerous due to risk of explosion Liquid oxygen & liquid nitrogen are transported on roads daily, light weight insulated containers safely ‘leak away’ excess pressure 3 Be non toxic toxic Hydrogen & methane can be breathed in, in small amounts without harm Butane, octane have narcotic and hallucinogenic properties in small amounts, and poisonous in larger quantities Ethanol poisonous in small amounts, taken continuously causes long term damage to organs of the body 4 Have a high high calorific value (high energy density) Hydrocarbons of increasing increasing molecular mass are superior giving lots of energy due to large amounts of bonds, uncompressed (hydrogen)gases are inferior  ∆ Hc(C8H18) = –5510kJmol –1 density 0.703gcm –3 Calculate the calorific value per gram and per cm3 1 mole C8H18 = 114g 1cm3 of octa octane ne has has a mass mass of 0.70 0.703g 3g 114g 114g of octa octane ne yiel yields ds 5510 5510kJ kJ on comb combus usti tion on  –1 3  –1  –3 1g yields 5510kJ/114g = 48.3kJg = calorific value 1cm yields 0.703g x 48.3kJg = 34.0kJcm = calorific value 5 Give rise to harmless harmless combustion products (little (little pollution) Hydrocarbons can give CO(poisonous) and carbon(soot) if there’s insufficient air or fuel is not correctly mixed High temp of combustion can form toxic nitrogen oxides from the air used to burn the fuel: N2(g) + O2(g) 2NO(g) followed in atmosphere by 2NO(g) + O2(g) 2NO2(g) contributing to formation of acid rain, as nitric acid and by oxidising sulphur dioxide to sulphuric acid H H H H H H (1)(i)Write (1)(i)Write the full structural formula of buta-1,3-diene H C C C C H H C C C C H (ii)Give structural formula of product of reaction of buta-1,3-diene with alkaline solution of potassium manganate(VII) manganate(VII) O H O H O H O H H H (i) (ii)

(2)(a)Explain (2)(a)Explain the difference in reactivity of ethane and ethene with bromine in terms bonding (a)Ethane single bonds/sigma only • C-H must be broken • Ethene also also has sigma and pi bonds • where electrons are more more accessible/pi bond is weaker(and breaks) (3)(a)State with reason reason the empirical formula of polypropene polypropene (a)CH2 as polymer made by addition reaction/no loss of small molecules (4)(a) (4)(a)Wr Write ite equa equatio tion n for comp complet letee combus combustio tion n of hydro hydrogen gen

(a)2H (a)2H2 + O2 → 2H2O (b)Why does methane not react with air unless a flame or spark is applied to the mixture? (b) • Activation energy needed needed • before reaction reaction can proceed at reasonable rate rate (5)What does methane methane do in the industrial production production of ammonia? ammonia? (5) • Source of hydrogen hydrogen • Source of heat (energy)to run process (6)(i)Draw the structural formula of a compound which is an isomer of but-2-ene but which does not show geometric isomerism (ii)Explain why the isomer drawn in (i) does not show geometric isomerism H H

C 2H C

C

5

H

C H C

C

H C

3

H

C

C

C H

3

C H

2

C H

2

C H

2

C H

2

H H C H 3 H H (6)(i) H (ii)One end of C=C bond has 2 identical atoms/groups attached OR if cyclobutane, no C=C (7)Draw full structural formulae for  (i)The organic product of the reaction of ethene C2H4 with

(aq)potassium manganate(VII) manganate(VII) and H2SO4 (ii)3,4-dimethy1hex-2-ene

H H

H H H

C

H C

H C

H

H

C

C

C

H

H

H

C

C

C

H

H

H H

H

C

H

H

H (ii) (8)( (8)(a) a)St Stat atee the the rela relati tion onsh ship ip betw betwee een n 2,2, 2,2,44-tr trim imet ethy hylp lpen enta tane ne and and octa octane ne (a)s (a)str truc uctu tura rall isom isomer erss (b)Octane has to be vaporised before burning in an engine. Determine fuel to air ratio by volume for complete combustion combustion of octane(g) (b)2C8H18 + 25O2 → 16CO2 + 18H2O air is 20%O2 therefore 2:125

(7)(i)

O H

O H

(c)Lead tetraethyl used to be added to petrol to boost its Relative Octane Number but this has now been replaced by compounds such as  benzene or MTBE(not so effective as the lead compound and so need to be added in larger quantities causing solubility problems) (i)Why has the addition of lead tetraethyl to petrol been stopped in the UK? (i)lead is poisonous/ruins catalyst in catalytic converters (ii)How might the difficulty in keeping MTBE in solution in the petrol cause a problem in the running of the car? (ii)RON may not be maintained maintained OR fuel can cause knocking/pre-ignition knocking/pre-ignition (iii)Apa (iii)Apart rt from from solubili solubility, ty, state state one one problem problem associate associated d with the use use of benzene benzene as as an additiv additivee to petrol petrol (iii)ben (iii)benzene zene is carcinoge carcinogenic nic (9)(a)Draw a diagram to show the shape of the chloromethane molecule and explain why it has this shape (b)Explain why the Bt of chloromethane is higher than that of methane

(c)Explain why the Bt of methanol is higher than that of chloromethane H (a)4 pairs of electrons around C arranged to minimise repulsion C (b)chloromethane (b)chloromethane has a (permanent)dipole, methane only has van der Waals forces H C l • attraction(forces) attraction(forces) between between dipoles stronger than Vdw in CH 4  Increase in number of electrons in molecule, causes H (a) increase in VDW forces of attraction between molecules (c)H bonding in methanol between molecules stronger than dipole-dipole/VDW forces (10) Ethane and chlorine react when exposed to light H C H

3

C

H

H H

+

C l

C H

3

C

+

H

C l

C H

3

C

H +

C l

C l

C H

3

C

Cl

+

C l

H H H H step 1 step 2 (a)Explain the movement of the C-H bond electron pair in step 1 (a)1 electron goes to the C atom (to form a radical) the other goes to form a bond with the Cl atom Haloalkanes CnH2n + 1X Compounds formed when a member of the halogen group is substituted into an alkane  Numbe  Numberr indica indicatin ting g haloge halogen n posi positio tion n on C chainchain- haloge halogen n namename- alkane alkane name name H H H H | | | | CH3Cl Chloromethane Carbon–Halogen bond is polar   Cl–C–Cl H–C–C–C–H \ δ+ δ–  CH3CH2Br Bromoethane | | | | CH3CH2CH2Br 1-bromopropane  –  C  X (halogen more EN than carbon) Cl H I H / displacement of bonding electron pair  CH3CHBrCH3 2-bromopropane trichloromethane 2-iodopropane CH2Br  CH3 F Br  | | | | CH3 –CH–CH3 CH3 –C–CH2 –Br  F–C–C–H 1-bromo-2-methylpropane | | | CH3 F Cl 1-bromo-2,2-dimethylpropane 1,3-dimethylcyclopentane 2-bromo-2-chloro-1,1,1-trifluoroethane Functional group An atom/group of atoms/structural feature in a molecule which has chemical properties not shown by an alkane(determines alkane(determines reactions) - All reactions of haloalkanes are reactions of the halogen atom(functional atom(functional group) Atoms other than C and H are more reactive than hydrocarbon chain which can only react like alkanes. alkanes. Carbon–halogen bond easier to break than C–H bonds Structural isomerism • Moving the halogen halogen atom to different different positions on on the C chain • Branching of the the C chain in larger larger molecules Hydrocarbon chain to which a functional group is attached can exist in one of 3 possible forms R 1 R 2 R 3 are alkyl groups which maybe the same or different but must contain at least one C atom - Same types of reaction for all 3 types of haloalkane but difference in rate of reaction - No compound with fewer fewer than 4 C atoms per molecule can can form a tertiary C compound compound H No fewe fewerr tha than n 2H 2H ato atoms ms atta attach ched ed H One H atom attached R 3  No H atom on functional group C atom | to func functtiona ionall grou group p C atom tom | to func unctio tional nal grou group p C atom tom | R 1 –C–X R 1 –C–X R 1 –C–X | –CH2X primary 1° | –CHX se secondary 2° 2° | –CX tertiary 3° H R 2 R 2 Rates of reaction of haloalkane depends on: Bromides Chlorides • Nature of of the halogen Iodides   React quickest because React slowest because - Largest atoms - Smallest atoms - C– C–I bond is longer easier to break - La Larger bond energy - Lower bond energy energy • Type of haloalkane haloalkane 1° compound 2° compound 3° compound   Reacts quickest Reacts slowest - Haloalkanes are polarised molecules, molecules, Mt higher than alkanes of the same length, dipole-dipole interactions interactions exist between chains Elimination reaction Elements of a simple molecule(H2O)are removed from the organic molecule and not replaced by any other  atom/group of atoms Nucleophilic substitution δ+ C atom can be attacked by a nucleophile OH – , CN – , NH3 nucleophiles which react with haloalkanes :OH –  prov provid ides es a pai pairr of of ele elect ctro rons ns for for C C–Br C–Br bond bond brea breaks ks  –   –  heterolytically, heterolytically, both electrons from the bond taken by Br  then OH bonds to C Test for haloalkanes nucleophilic substitution reaction • Warm haloalkane haloalkane with NaOH(aq) CnH2n + 1X + OH – (nucleophile) CnH2n + 1OH + X – (halide ion) • Silver nitrate test, Acidify Acidify with (dil)nitric (dil)nitric acid to remove excess OH –  which could react with Ag + • Add silver silver nitrate(aq) nitrate(aq) Ag+(aq) + X – (aq) AgX(s) Result: Result: - AgCl, AgCl, White White ppt, dissolves dissolves in (dil)NH (dil)NH3 to give a colourless solution - AgBr, Cream ppt, partially partially dissolves dissolves in (dil)NH3 but dissolves in (conc)NH3 to give a colourless solution - AgI, Yellow ppt, insoluble in in NH3 solution of any concentration C–Cl bonds in compounds used as herbicides, weedkillers weedkillers for crops, insecticides, DDT, C–Cl bond is sufficiently inert to give compound longish life but survival in environment causes problems as DDT is toxic to insect eating birds which accumulates toxic compound in  body fat

2-bromopropane (haloalkane) CH3CHBrCH3 + OH –  Heat under reflux, hydrolysis(halogen atom displaced by OH group)

Haloalkane reaction with NaOH/KOH

KOH/NaOH(aq) KOH/NaOH(ethanol) Aqueous conditions favour nucleophilic substitution, Anhydrous conditions favour elimination, OH –  acts as a nucleophile OH –  acts as a base  –  Propan-2-ol(Alcohol)CH3CHOHCH3 + Br Propene(Alkene) CH3CH=CH2 + Br –  + H2O 1-chloropropane CH3CH2CH2Cl(l) + NaOH(aq)  propan-1-ol CH3CH2CH2OH(aq) + NaCl(aq)  –   –  CH3CH2CH2Cl + OH CH3CH2CH2OH + Cl CH3CHBrCH3 + KOH(ethanol) CH3CH=CH2 + KBr + H2O Depending on which H atom is removed it’s possible to form 2 different alkenes in the same reaction H Br Br H | | Heat under reflux | | Heat under reflux CH2CHCH2CH3 + KOH(ethanol) CH2=CHCH2CH3 or CH3CHCHCH3 + KOH(ethanol) CH3CH=CHCH3 2-bromobutane but-1-ene 2-bromobutane but-2-ene  –   –  Haloalkane reaction with NH3(ethanol) Nucleophilic substitution reaction :OH : NH  NH3 nucleophiles, :OH stonger base than : NH  NH3 heat in sealed container heated in sealed container   (ethanol)H3N: + RI (primary amine)RNH2 + HI CH3CH2Br + NH3(ethanol) CH3CH2NH2 + HBr ethylamine For every ammonia molecule reacting in this way one maybe prevented from reacting by the acid produced H3N: + HI NH4+ I  –  Ammonia ion no longer a nucleophile, thus minimum of 2 moles of ammonia to every mole of haloalkane 2H3N + RI RNH2 + NH4I More ammonia must be used because amine product is a nucleophile RN:H2 + RI (secondary amine) R 2N:H + HI - Anhydrous conditions, ammonia ammonia dissolved in alcohol not water as water is another competing nucleophile NH3 + H2O NH4+ + OH –  - Huge excess of cheap ammonia used, reaction normally done in a closed vessel under pressure because of  • volatility of ammonia ammonia • need to heat - Boiling under reflux not suitable for reactions reactions of haloalkanes with ammonia because, ammonia is a volatile material material boiling well  below RT and escaping from top of condenser as Bt of ammonia is well below temp of water in cooling jacket of condenser  Haloalkane reaction with KCN(ethanolic) Heat under reflux, Nucleophilic substitution CH3CH2I + CN  –  CH3CH2CN CH3CHBrCH3 + KCN(ethanol) CH3CHCNCH3 + KBr Iodoethane(Haloalkane) Iodoethane(Halo alkane) Nucleophile Nucleophile Propanenitrile(Cyanides/Ni Propanenitrile( Cyanides/Nitriles) triles) Heat acid, Hydrolysis (Nitrile)CH3CH2CN + 2H2O (Carboxylic acid)CH3CH2COOH + NH3 (1)(a)Why is the rate of reaction slower with bromobutane than with iodoethane (a)C–Br bond stronger stronger than C–I • Ea for C–Br is higher than C–I C–I (b)CH3CHBrCH2CH3 + KOH CH3CHOHCH2CH3 + KBr Experiment repeated repeated except 2-iodobutane replaced replaced 2-bromobutane

Explain effects that this change would have on rate of reaction (b)Rate increased C-I bond weaker(than C-Br bond)/lower bond)/lower bond energy (2)Product C2H4Br 2 is a bromoalkane. Suggest the structural structural formulae of each of the products products of the reaction of C2H4Br 2 with the reag reagen ents ts giv given en bel below ow and and ide ident ntif ify y the the type type of of reac reacti tion on inv invol olve ved d (i)N (i)NaO aOH( H(aq aq)P )Pro rodu duct ct?? Type Type of of reac reacti tion on?? (ii)NaOH(ethanol) (ii)NaOH(ethanol) (heated under reflux) Product? Type of reaction? H

H

H

C

C

O H O H

H

or

H

H

H

C

C

B r

O H

C H H H (1)

C

C

H

o r

H

H

H

C

C

C H

3

C B r

C

H

(1)

C H 3C H

3

H H

A

(i) nucleophilic substitution (ii) elimination (iii)Suggest, (iii)Suggest, giving the reagents and conditions, how compound A could be converted in 2 steps into compound B (iii)Step 1 is production of halogen intermediate(HCl)at RT Step 2 alcohol or hydrogen sulphate sulphate followed by alcoholic KCN • heat under reflux reflux 1 2 Aldehydes & Ketones CnH2nO R  & R  are alkyl groups which maybe the same or different Aldehydes Aldehydes Alkanal Ketones Ketones HCHO Methanal C atom in functional group CH3COCH3 CH3CHO Ethanal CH3CH2COCH3 CH3CH2CHO Propanal CH3CH2CH2COCH3 CH3CH2CH2CHO Butanal CH3CH2COCH2CH3 1 1 2 (CH ) CHCHO 2-methylpropanal 3 2 R  can be a H atom R  & R  must contain at least

C

C

H

3

C N

H B

Alkanone Propanone Butanone Pentan-2-one Pentan-3-one

one C atom Test for carbonyl(C=O)group(aldehydes & ketones) Add excess of(2, 4-dinitrophenylhydrazine)Brady 4-dinitrophenylhydrazine)Brady’s ’s reagent solution and ppt of orange/yellow orange/yellow Test for aldehydes(-CHO) group(not ketones) Aldehydes are good reducing agents unlike ketones –CHO + [O]  -COOH • Fehling’s/Benedict’s Fehling’s/Benedict’s solution both both reduced from blue from blue Cu2+ complexes  brick-red Cu2O (copper(I) oxide) + • Tollen’s reagent reagent [Ag(NH [Ag(NH3)2] when warmed is reduced to silver  silver (silver (silver coats inside of apparatus) (Making Tollen’s reagent: few drops of dil NaOH to silver nitrate solution, then adding dil ammonia solution until brown ppt dissolves) • Heated under reflux, potassium potassium dichromate(VI) dichromate(VI) solution changes from orange  green Carboxylic Acids CnH2n + 1COOH Alkanoic Acid n = 0 HCOOH Methanoic acid n = 1 CH3COOH Ethanoic acid CH3CH2COOH Propanoic acid CH3CH2CH2COOH Butanoic acid Alcohols CnH2n + 1OH  Number inserted before –ol indicates position of –OH(functional group)on C chain CH3OH Methanol Fuel(unleaded petrol), plastics, dyes CH3CH2OH Ethanol Alcoholic drinks, methylated drinks, fuel, as a solvent in perfumes/cosmetics

CH3CH2CH2OH Propan-1-ol CH3CHOHCH3 Propan-2-ol 1° alcoh al cohol ol C atom which carries the –OH 2° alcoh al cohol ol C atom which carries the –OH 3° alco al cohol hol C atom which carries group attached to only 1 alkyl group group attached to only 2 alkyl groups the –OH group attached to 3 alkyl groups Combustion, oxidation reaction CH3CH2OH(l) + 3O2(g) 2CO2(g) + 3H2O(g) Test for –OH compound Sample of alcohol in a clean dry test tube(steamy acidic fumes with any –OH compound, water contains  –OH group producing fumes of HCl which invalidates test) RT RT ROH + PCl5(s) RCl + POCl3 + HCl CH3CH2OH + PCl5(s) CH3CH2Cl + POCl3 + HCl Phosphorus pentachloride Ethanol Chloroethane Heat under reflux 2P + 3I2 2PI3(l) PI3(l) + 3ROH(l) H3PO3(l) + 3RI(l) Iodoalkane Moist red phosphorus Phosphorus trihalide (distilled off)  Nucleophilic substitution reaction Hal –  nucleophile, attracted towards polarised polarised C atom in Cδ+ –Oδ–  and –OH snaps off  ROH + HX RX + H2O - HI acid not a laboratory laboratory reagent since it’s rapidly rapidly oxidised in air  in the place where reaction is occurring ) alcohol mixed with Na/KBr + concH 2SO4 - HBr made made in situ( situ(in Reflux KBr + (conc)H2SO4 KHSO4 + HBr HBr(g) + CH3CH2OH(l) CH3CH2Br(l) + H2O(l) 3° alcohols react reasonably rapidly with conc HCl but 1°,2° alcohols react slow OH Cl | Shake at RT | CH3 –  – C – CH3 + conc HCl CH3 –  – C – CH3 + H2O | | CH3 CH3 2-methyl-propan-2-ol 2-chloro-2-methylpropane 3° alcohol 3° haloalkane -OH with Na produces alkoxides 2CH3CH2OH(l) + 2Na(s) 2CH3CH2O – Na+ + H2(g) The longer the alcohol chain, the less reactive it is with Na Ethanol Ionic sodium ethoxide(colourless solution) Polar –OH groups on alcohols helps them to form H bonds H bonds form between –OH and H2O Larger the alcohols, the less miscibility in water, larger alcohols are mostly non-polar C chains, so less attraction for polar H 2O because of H bonding alcohols have high Bt compared to non-polar compounds(alkanes compounds(alkanes of similar size, weaker Vdw forces) Isomeric alkenes with more than one adjacent CH group Dehydration (alcohol should have an H atom on α–C atom(C atom next to H OH H H that which carries the –OH)) | | | | Elimination reaction Butan-2-ol Butan2-ol H–C–C– H–C–C–C–C–H C–C–H | | | | H H H H 170°C excess(conc)H 2SO4/70°C H3PO4 phosphoric(V)acid

Method 1 Heating alcohol with excess conc H 2SO4 (dehydrating agent in elimination reaction) Alkene produced collected over water  Method 2 Hot alcohol vapour passed over a hot catalyst of  aluminium oxide(vapour phase dehydration, air must be excluded)Al2O3 catalyst(large catalyst(large surface area for reaction, crushing into blocks/powder) Al2O3 Ethanol CH3CH2OH Ethene CH2=CH2 + H2O(g) Catalyst conc H 2SO4 is a strong oxidising agent and oxidises some of the alcohol to CO2 and is reduced itself to SO2 both gases needing removal from the alkene, therefore therefore gases passed through NaOH(aq). NaOH(aq). Alkene is collected over water 

[O] = (one atom of) oxygen has been added from an oxidising agent • Reactants aren’t mixed mixed in bulk at start because of vigour of of the reaction. Ethanol and conc H2SO4 slowly added from a separating funnel to [O] • 1° alcohol converted to an aldehyde if excess alcohol is used(so there’s insufficient oxidising agent to carry out 2nd stage) and aldehyde formed is distilled off immediately before further oxidation(aldehyde oxidation(aldehyde boils at lower temp than alcohol). Fractional distillation distillation for  increasing purity of ethanal and obtaining a good specimen 3CH3CH2OH + Cr2O72–  + 8H+ 3CH3CHO + 2Cr3+ + 7H2O ethanol ethanal • 1° alcohol converted directly to carboxylic acid by heating under reflux with excess[O]ensuring reaction does not stop at aldehyde stage  simplified  3CH3CH2OH + 2Cr2O72–  + 16H+ 3CH3COOH + 4Cr3+ + 11H2O CH3CH2OH + 2[O] 3CH3COOH + H2O ethanol ethanoic acid Yield obtained x 100 % Yield = Theoretical Yield Organic preparations are designed to consume a material completely because • Material difficult difficult to remove remove unchanged from the the product • Material is expensive Calculate the theoretical theoretical yield yield of bromoethane from 12g of potassium potassium bromide CH3CH2OH + KBr + H 2SO4  CH3CH2Br + KHSO4 + H2O Mr (KBr) (KBr) = 119gmol  –1 Amount of KBr = 12g/119gmol  –1 = 0.101mol = Amount of CH 3CH2Br  Mr (CH (CH3CH2Br) = 109gmol  –1 Theoretical yield = 109gmol  –1 x 0.101mol = 11g If 5g of bromoethane is obtained then %Yield = 5 x 100/11 = 45% (1)Alcohol Z heated with (conc)sulphuric acid, gas Y produced which reacts with bromine solution decolourising it. Draw functional group in in Y (1)C=C

C 3H 6 Propene

step 1

C 3H

7

B r ( m a jo r p r o d u c t )

S

s te p 2

K M n O 4 in alkali

a q ue o u s N a O H C 3H

Q

8

O

P

s te p 3 oxidation C H 3C O C H

(a)(i) (a)(i)Gi Give ve the the reagen reagentt and the the condi conditio tions ns need needed ed for for step step 1 (a)(i (a)(i)HB )HBr(g r(g)) (ii)State the type of reaction in, step 1, the conversion of S to P (ii)electrophilic addition, nucleophilic substitution/hydrolysis (b)(i)Give the reagent and the conditions needed for step 2 (b)(i)170°C (conc)H2SO4/70°C H3PO4/aluminium oxide heat (ii)Give the reagents and the conditions needed for step 3 (ii)H2SO4 acidified potassium dichromate(VI) dichromate(VI) heat under reflux (c)Give the structural structural formula formula for Q (c)CH3CH(OH)CH 2OH (d)Draw the full structural formula showing all the bonds for the isomer of   butan-2-ol that is a tertiary alcohol H H

3

H C

H

C H

H

3

or

H

(d)Methylpropan–2–ol

C

C

C

H

O H

H

H

C H

3

C

C H

3

O H

Four of the structural isomers of C 4H10O are alcohols. One of these isomers is butan-2-ol (a)Draw the structural formulae of 2 other alcohols with molecular formula C 4H10O and name them H H

H

H

H

C

C

C

C

H H (a) Butan-1-ol

H

H

H

O H

H

H

H H

C

H H

C

C

C

H

O H

H

H

H

(2)-methylpropan-1-ol,

H H

C

H H

C

C

C

H

H

H

O H

(2)-methylpropan-2-ol

(b)butan-2-ol heated with H2SO4 acid and potassium dichromate(VI), name the product and name type of reaction (b)butan-2-one, oxidation/redox K 2 C r 2 O 7 in •None of the compounds in the scheme shows cis-trans isomerism d i l u t e s u l p h u r ic •D reacts with KCN to form 2-methylpropanonitrile C 3 H 8O acid C 3H 6O •An isomer of A will form C by the same route but will not produce B by reaction with potassium A B dichromate(VI) dichromate(VI) acidified with (dil) H2SO4 Instead it makes E, C 3H6O2 Identify using a name or structural formulae:A,B,C,D,E formulae:A,B,C,D,E c o n c s u l p h u r ic a c i d

C

 A Propan-2-ol

 B Propanone

C  Propene

 D 2-bromopropane

 E  Propanoic acid

D

H B r

(a)P (a)Pro ropa pann-11-ol ol to 2-br 2-brom omop opro ropa pane ne in 2 stag stages es?? (a)C (a)CH H3CH2CH2OH → CH3CH=CH2 → CH3CHBrCH 3 One of the isomers of C4H10O is the alcohol 2-methylpropan-2-ol (b)Draw the structural formula of the final organic product of the which has the structural formula reaction when each of the three alcohols in (a)(i) is heated under  C H 3 reflux with a solution of potassium dichromate(VI) in (dil)H 2SO4 C H

C

3

C H

3

H

O H

(a)Draw structural formulae of 3 other structural isomers of  C4H10O which are also alcohols H

H

H

H

H

C

C

C

C

H

H

H

H

O H

(a)

H

H

H

H

H

C

C

C

C

H

H

O H H

H

(b)

H

H

H

H

H

C

C

C

C

H

H

H

H

H

H

H

H

C

C

C

C

H

H

O H H

O H

H

H

H

H

H

H

O H

C

C

C

C

H

H

H

H

H

C

C

C

C

H

H

O

H

H

C H

C

C

C

O

H

H

O H

O (1)

H H (1)

H H H

H

C

H

H

C

C

C

H

H

H

O H

H

H

C H

C

C

C

H

H

H

3

H O H

H

3

(1)

Propanone Bt 56°C prepared by oxidising propan-2-ol Bt 82°C (H 2SO4 potassium dichromate(VI)) Boil mixture for 15minutes (a)What safety precaution precaution in addition to wearing eye protection must be taken when adding the concH2SO4? (a)Gloves/add slowly/cool while adding NOT adding NOT lab coats/be careful not to spill on hands/do in fume cupboard  (b)Outline how you would obtain propanone from this aqueous mixture after it had been boiled for 15 minutes (b)(Fractionally)distil, (b)(Fractionally)distil, collect fraction that distils at 55-57°C

• Catalysts provide provide an alternative route route for a reaction which has a lower Eact than normal route, thus more molecules having enough energy to overcome the Eact - Catalyst has no effect effect on ∆ H of the reaction or amounts of   products - Catalysts used in petroleum petroleum industry(longer industry(longer chain alkanes are cracked into shorter more useful molecules using zedite catalyst) S2O82– (aq) + 2I – (aq)  2SO42– (aq) + I2(aq) Catalysed reaction: Step1 S2O82– (aq) + 2Fe2+(aq)  2SO42– (aq) + 2Fe3+(aq) Step2 2Fe3+(aq) + 2I – (aq)  2Fe2+(aq) + I2(aq)

Catalyst

Factors which affect rate of chemical reaction • Concentration of reactants in solution • Temperature •  Pressure of any gases present present • Surface area of any solid reactants •  Light (certain (certain reactions) • Catalysts substances which increases rate of chemical reaction without being chemically changed themselves 2 theories of kinetics, collision theory and transition state theory Collision theory Before 2 particles react they must collide, only a small fraction of the total collisions results in a reaction because: Molecules must have correct Direction of approach (Steric factor )2 factor )2 molecules traveling in approx same direction with high KE may not produce a high energy collision Orientation If bulk of molecule protects functional group from attack in a high energy collision then a reaction may not occur  Activation energy Certain minimum amount of KE that must be provided to reactants in a chemical reaction so they can start a reaction (reach an activated state from which products can form) Reaction rate increased if: • Concentration, pressure increased  More particles in a given volume, collisions occur more frequently •  Surface area increased  More collisions between solid surface and other reactant • Temperature increased  Proportion of molecules having Eact increased, KE’s of molecules are increased along with frequency of  collisions, overall increase in number of effective of effective collisions per second •  Shaking a container  helps to increase the rate of heterogenous reactions(solid reactions(solid settling out from a liquid) Shaking brings the reactants together increasing frequency of collision Maxwell Boltzmann distributions of molecular energy in a Maxwell Boltzmann distribution Way in which energies are sample of gas at T1 & T2 distributed, molecules in a gas/liquid don’t all have the same KE since they don’t all have the same speed, only a few molecules will have very low/high energies most being around the most common value represented by the peak 

- As temperature increases • Curve broadens out • Peak value decreases moving moving towards a higher energy value value • Area under curve represents represents total number of molecules molecules in sample and is therefore constant

• Curve starts at (0,0) (0,0) because no molecules have 0 energy energy • Area under the curve beyond beyond Eact represents number of  molecules having energies greater than or equal to Eact which increases with temperature and rate of reaction Transition state theory As 2 molecules approach each other, repulsion between their electron clouds will push them apart unless they have sufficient KE to overcome the repulsion. If they do get sufficiently close to each other, a rearrangement of electron clouds will occur so that some bonds are broken and new  bonds form. While this is happening a highly unstable species species is formed in which some bonds are partially broken/formed(activated broken/formed(activated complex) and KE of collision is converted into PE

Thermodynamic stability A mixture is thermodynamically thermodynamically unstable Either  unstable Either as as the reaction is very exothermic Or energy Or energy level of   products below energy level of reactants - A substance(mixture) mostly converted converted into something else at equilibrium is thermodynamically thermodynamically unstable(exothermic unstable(exothermic reaction, products more stable than reactants) Free energy needs to considered in determining determining whether or not a reaction is spontaneous(forward reaction) reaction) thermodynamically feasible reactions Kinetic stability Reaction is kinetically stable when Eact is high (When reactants fail to undergo thermodynamically they are kinetically stable) (1)(a)If a mixture is thermodynamically thermodynamically stable, can it be kinetically stable? (1)(a)No, kinetic stability describes describes a condition in which a thermodynamically unstable unstable substance/mixture fails to react. If a substance/mixture substance/mixture is thermodynamically thermodynamically stable it isn’t going to react(to give the products with which its stability is being compared) (b)Explain the terms thermodynamic and kinetic stability with reference to the combustion of graphite (b)• Reactants are are at a higher higher energy level(than products) • So CO2 products are thermodynamically stable with respect to reactants • C(+O2)activation energy high enough to prevent appreciable reaction at RT so mixture/C(+O mixture/C(+O2) is kinetically stable  –1 (c)CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ∆  H c(CH4(g))= –890 kJ mol Methane doesn’t burn unless lit

Use this information to explain the difference between thermodynamic and kinetic stability (c) • CH4(and O2)/reactants thermodynamically thermodynamically unstable with respect to products • Since reactants reactants are at at a higher energy level(than level(than products) • Reactants/methane, Reactants/methane, oxygen are kinetically kinetically stable due to high Ea (d)Why would a reaction expected to take place, proceed slowly as to appear never to happen? (d)• Reaction has has high Eact • Reactants kinetically kinetically stable (e)CH4 (l) + 2O2 (g)  CO2 (g) + 2H2O (g) ∆  H θ = -890kJmol  –1 Why would you expect the reaction to take place? (e)Products more thermodynamically stable than reactants (c)A mixture of nitrogen and hydrogen is kinetically stable at 25°C but kinetically unstable at 400°C. Explain why (c)• At 25°C few collisions have E ≥ Ea/sufficient energy to react • At higher temp(average)energy of molecules increases • At 400°C more molecules/collisions have E ≥ Ea/sufficient energy to react Reversible reaction A reaction that doesn’t go to completion and occurs in both the forward and reverse direction Rate of reaction from left to right starts at a certain level but decreases as the concentrations of the reactants decrease. decrease. Reverse reaction will not start start until some  products have formed. Point reached when forward forward and reverse reactions reactions will be occurring at the same rate, where concentrations of substances will remain constant but reactions haven’t stopped Dynamic equilibrium Rate of forward reaction and reverse reactions equal and there are no concentration changes • Dynamic equilibrium equilibrium will only be be achieved in a closed system(rates system(rates of  condensation & evaporation are equal, if gas escaped then reverse reaction couldn’t occur) • Same equilibrium equilibrium achieved provided temperature temperature is constant Position of equilibrium Extent of a reaction when equilibrium is established. established. If reaction uses more than 50% of reactants before reaching equil then POE lies to RHS Factors which might affect POE: POE : Changing concentration on POE  nA + mB + xC pP + yQ Increasing concentration concentration of a reactant and POE moves to RHS. Increasing concentration concentration of A means more A will react with B & C giving more P & Q until equilibrium is restored. Argument applies safely to concentration NOT amount, A + B C + D Adding more A(all gases at atmospheric pressure)increases pressure)increases total vol, conc of A increases and reduces concentrations of all other species Changing  pressure  pressure on POE  • Only affects affects gaseous equilibria equilibria • And only if there is a change change in total number of molecules Increasing pressure on an equilibrium mixture pushes POE towards side with smaller number of molecules Increasing pressure moves POE to RHS in this reaction N2(g) + 3H2(g) 2NH3(g) 4 molecules 2 molecules Changing temperature on POE  Affects reactions which involve a ∆ H If temperature raised raised POE moves in the endothermic endothermic direction In an endothermic endothermic reaction reaction hydrogen formed favours favours high temperatures temperatures H2O(g) + CO(g) H2(g) + CO2(g) ∆ H = + 41kJmol  –1 Rate of attainment attainment of equilibrium • Increase in concentration, concentration, temperature, pressure(if pressure(if gases), increases increases rate of attainment of equilibrium equilibrium • Rates of both forward and reverse reactions increase(lower increase(lower activation routes for both)so catalyst catalyst will increase rate at which equilibrium is established but POE remains unaltered

Catalytic converter in the exhaust system of a car engine 2NO(g) + 2CO(g) 2CO(g) N2(g) + 2CO2(g) (i)Which way will the POE shift if temp temp were lowered (i) • To RHS RHS • Exothermic direction (ii)Gases from from engine aren’t cooled before entering entering converter, why? why? (ii)• Rate of reaction would be too slow if cooled • Yield too small small (a)Effect of catalyst catalyst on on rate of reaction? reaction? (a)• Alternative routes • Lower E act • Increase in rate rate because more successful successful collisions (b)Why is the catalyst in the form of a gauze/mesh? (b)Increased surface area (c)Explain why: When a tiny electric spark is produced in a mixture of methane and oxygen at 10°C the heat transferred is NOT sufficient to raise the temperature of the mixture by even 1°C yet the reaction occurs with explosive violence (c)When a tiny electric spark passes through the mixture mixture molecules in immediate vicinity obtain obtain enough energy to react. The resulting highly exothermic reaction raises the temperature of the surrounding molecules which also react and a wave of reaction passes outward from the spark until reaction is complete (d)Suggest why neutralisation of HCl by NaOH solution is virtually instantaneous (d)Enormous speed of neutralisation of acids by alkalis as E act is low, since no bonds need to be broken and reaction occurs by collision of oppositely charged ions which which are drawn together together by electrostatic electrostatic attraction attraction H+(aq) + OH –  (aq)  H2O(l) (e)Why do concentrations concentrations of substances in an equilibrium mixture remain constant? (e)Rates of forward and back reactions the same (f)Industrial catalysts(platinum) catalysts(platinum) are finely divided, and fine wire or mesh is preferred to powder, why? (f)Fine powders, unless “stuck” on a support, either block the flow of gases or tend to be blown away and may contaminate the product (g)Although speed is important in industry there is often quite a low upper limit to the temperature of industrial reactions, why? (g)Many industrial reactions reactions are exothermic equilibria. Raising the temperature temperature increases the reaction rate but makes the POE less favourable. A compromise has to be found between these conflicting effects(other effects(other methods of increasing the rate maybe used, such as increasing the pressure/concentration, using catalysts) (h)Sketch Maxwell-Boltzmann Maxwell-Boltzmann distribution representing energies of the molecules in the Ostwald reaction system at a given temp

Fraction o f  m o l ec u le s

E ac a t

E au n c a t

(h)

Energy

2g of Mg ribbon reacts with 100cm³ of H2SO4 acid 1moldm – 3 (a)Explain why the hydrogen is produced at a faster rate at the beginning of the experiment than it is at the end of the experiment • Higher conc of acid • Greater surface area area of magnesium • More collisions per second second and therefore a faster rate rate  –1 Haber Bosh process N2(g) + 3H2(g) 2NH3(g) ∆ H = 92kJmol 200atm 400°C Iron catalyst Raw materials: CH4(g) + H2O(g) or  CO(g) + 3H2(g) C(s) + H2O(g) CO(g) + H2(g) natural gas steam Ni catalyst hydrogen obtained Coal CO would poison the catalyst, CO removed through air injection, CO oxidised to CO2 and removed Economic factors factors in increasing rate of reaction reaction & yield: • Containers operating operating at high pressures are expensive expensive to build and maintain, high costs exceed value of extra product. Reduction in temp slows down rate at which equilibrium is attained attained but catalysts usually last longer at lower temps - Catalysts increase increase rate of reaction & rate of attainment of equil but doesn’t affect POE, they’re they’re susceptible to poisoning by impurities so incoming gases are purified - Equilibrium mixture mixture formed is passed into refrigeration plant because it allows NH3 to be liquefied and removed, unreacted gases can be recyc recycled led if prod product uct can can be remov removed, ed, thus thus allow allowing ing a conti continuo nuous us flow flow proce process ss (NH (NH3(g)removed, N2(g) + 3H2(g) recycled) - Compromise of conditions pushing POE to RHS RHS balancing against keeping rate of reaction at a reasonable level - Periodically gases gases in Haber plant are ‘purged’(cleared out)and fresh gas put in. Air contains 1% argon which builds up if it isn’t removed(with traces of other noble gases) Uses:NH 3 used in detergents production of nitric acid and fertilisers NH4 NO  NO3 Ostwald process Nitric acid(HNO 3)manufacture 5atm 1000K Platinum rhodium catalyst - Combustion of CH4 gives CO2 + H2O, oxides (-ve)∆ Hf thermodynamically thermodynamically stable with respect to their elements - NH3 gives N2 + H2O, all common oxides of nitrogen have (+ve)∆ Hf less thermodynamically stable with respect to their elements - Ammonia not a flamm flammable able gas in air but will burn/oxidise burn/oxidise in oxygen 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) ∆ H = –1636kJmol  –1 Excess of hot air ensures complete oxidation of NH3 Platinum rhodium catalyst - Too low a temp and slower reaction may not go to completion, presence of NH3 in subsequent stages of nitric acid production disastrous Too high a temp and some NH3 oxidised to nitrogen + water, an economic loss of NH3 - Cooling of gases(cold air)as it leaves the catalyst catalyst before resulting gases are absorbed in cold water   –1 2NO(g) + O2(g) pushing equilibrium to NO2 since reaction is exothermic 2 g) ∆ H = –94kJmol - Passed into water water with excess excess air  4NO2(g) + O2(g) + 2H2O(l) 4HNO3(aq) NH3(aq) + HNO3(aq) NH4NO3(aq) (water soluble)powerful oxidising agent, dangerously explosive ammonium nitrate used in agriculture/fertiliser  agriculture/fertiliser  (1)Ammonia boils at -330°C but the liquefaction plant uses cold water to remove NH3 from the gas stream? (1)NH3 not dissolved in water, gas mixture at 200-300atm where Bt of NH3 is wabove RT thus easily liquefied at temp of cold water  (2)Industrially (2)Industrially this reaction doesn’t usually achieve equilibrium 2NO(g) + O2(g) 2NO2(g) why?

(2)Products removed from reaction system, not in the system long enough

Contact process Sulphuric acid manufacture 4atm 440°C vanadium(V)oxide catalyst (V 2O5) or  S(s) + O2(g) SO2(g) 2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) Burn in excess air  sulphide ore heat(roast) 2SO2(g) + O2(g) 2SO3(g) ∆ H = –200kJmol  –1 oxidation V2O5 SO3 reaction with water is an uncontrollable reaction creating a fog of sulphuric acid so H2SO4(l) + SO3(g) H2S2O7(l) Oleum  –1 H2O(l) + H2S2O7(l) 2H2SO4(l) ∆ H = –130kJmol - Provided temperature temperature is not too high little gained by high pressures with the difficulty and cost - Excess air and sufficient pressure to push gases round the plant ensures efficient oxidation oxidation - Competition between between low rates/temp with favourable POE and high rates/temp rates/temp with less favourable POE - SO2 ‘scrubbed’ with water before returning to the atmosphere 2NH3(aq) + H2SO4(aq) (NH4)2SO4(aq) (ammonium salt)fertiliser  salt)fertiliser   NH3(aq) + H+(aq)  NH4+(aq) Ca3(PO4)2(s) + 2H2SO4(aq) Ca(H2PO4)2(s) + 2CaSO4(s)  Natur  Natural al calc calcium ium phosph phosphate ate rock rock Calciu Calcium m dihyd dihydrog rogen en phos phospha phate te Uses:H2SO4 used in dyes, soaps, paint pigments, explosives, fertilisers, detergents, pharmaceuticals Extraction of aluminium Amphoteric oxide Can react like an acid or base forming water and salt Aluminium found raw in aluminosilicates(and aluminosilicates(and igneous rocks though there is no economic way of extracting it from clay) 1 Aluminium extracted from hydrated aluminium oxides(bauxite) Al2O3.H2O and Al2O3.3H2O High negative ∆ Gf  of its oxide ∆ Gf  makes electrolysis the method of extraction Raw material purified before extraction process(impurities in bauxite are iron(III)oxide and silica) Al2O3 reacts because it is amphoteric and dissolves forming a solution Impurities don’t react or dissolve because Fe 2O3 is basic and silica is too unreactive 2 High energy costs from bauxite being crushed & heated under pressure with conc NaOH(aq) Amphoteric aluminium oxide dissolves to give sodium aluminate solution + sodium silicate + iron(III)oxide Silica which is acidic, dissolves Iron(III)oxide doesn’t react with alkali because it’s a basic oxide and is left behind in a ‘red oxide mud’(can be removed by filtration) used to manufacture protective paint for ironwork  3 Blow CO2 Sodium silicate remains in solution Aluminium hydroxide is ppted and changes to insoluble hydrated aluminium oxide which is filtered off, washed and roasted to give pure aluminium oxide used in electrolytic electrolytic extraction of the metal Electrolytic Electrolytic extraction - Aluminium oxide Mt Mt 2040°C is high so unsuitable as as an electrolyte(economically electrolyte(economically because of heat heat energy costs) - Aluminium dissolved dissolved in bath of molten cryolite(NaAlF cryolite(NaAlF6)making electrolyte Mt1000°C by electric current 100000amps and 5V(DC) cell (only approx 2V to decompose oxide rest to overcome electrical resistance) - Carbon(graphite) Carbon(graphite) lining cathode, when DC current is passed through, aluminium forms at cathode and sinks to bottom of the tank  - Carbon(graphite) Carbon(graphite) anode electrodes are pure since aluminium is rarely purified after after production, carbon reacts with oxygen and erodes,  –   –  2O2 (solution) O2(g) + 4e C(s) + O2(g) CO2(g) - Anodes continuously fabricated fabricated by baking carbon paste(using cell heat)preventing heat)preventing need for stopping process when new anodes required - Anodes moved continuously as they erode maintaining maintaining constant dist(5cm) from the aluminium aluminium and to allow for change of depth of  aluminium between removal of batches of metal

- Great demand in electricity electricity of aluminium plant means means cheap and plentiful electricity electricity is desirable(hydroelect desirable(hydroelectricity) ricity) - High cost of aluminium makes recycling recycling economically effective, effective, conserving earths resources and energy, but quality makes it unsuitable for critical uses(manufacture of aircraft alloy) Uses: -Vehicle construction, construction, low density, mechanical mechanical weakness weakness of pure metal requires it to be alloyed alloyed to increase its strength. strength. - Manufacture of electrical cable for overhead overhead power lines, good electrical conductivity, conductivity, low density, cheaper than copper, supported  by a steel core to prevent it stretching stretching and breaking - High reflectivity, reflectivity, malleability means means its used in reflectors of car headlamps (1)Write 2 ionic half-equations to show corrosion of Fe by O2 and water  (1)Fe(s) Fe2+(aq) + 2e –  or

½ O2 + H2O + 2e –  2OH – 

(2)Explain why Fe corrodes faster than aluminium even though aluminium has a more negative standard electrode potential (2)Al covered with a protective layer of oxide iron is not covered by a protective layer/layer layer/layer is porous (3)E (3)Exp xpla lain in why why the the elec electr trol olyt ytee mus mustt be be mol molte ten n (3)S (3)So o tha thatt the the ions ions are are mob mobil ilee

Downs Process Electrolysis Electrolysis of electrolyte brine NaCl(aq) - Cell divided by a diaphragm which allows free passage of ions(under influence influence of electric field) but prevents mixing of products  because chlorine reacts with NaOH Overall reaction occurring in membrane cell 2NaCl + 2H2O 2NaOH + H2 + Cl2 - Before brine is electrolysed electrolysed it is treated with NaOH(or carbonate CO3) to remove traces of iron and calcium salts by precipitation and filtration(undesirable filtration(undesirable cations interfere with ion-exchange action of the membrane) - Brine flows into the anode compartment where the chlorine chlorine is liberated, piped off and used 2Cl  – (aq) – 2e –  Cl2(g) Anodes made of graphite or titanium which resist attack by liberated chlorine - Under influence of applied voltage, Na ions move through the membrane into the cathode compartment compartment where water is provided. Cathodes made of steel resisting attack by NaOH produced - Hydrogen liberated liberated and piped away for storage by reduction of water 2H2O(l) + 2e –  2OH – (aq) + H2(g) - Na ions and OH ions constitute constitute NaOH solution, they they do not form it, they are are it Uses: Manufacture NaOH, H2 and Cl2  NaOH purification of bauxite, manufacture of soap, bleaches Cl2 manufacture of PVC, insecticides, herbicides, bleaches H2 manufacture of HCl/methanol/margarine HCl/methanol/margarine Or rocket fuel/hydrogenation of oils  –  Cl2(g) + 2OH (aq) ClO – (aq) + Cl – (aq) + H2O(l)   NaOH NaOH Sodiu Sodium m chlora chlorate( te(I) I) househ household old bleach bleach  NaOH(aq) is cooled before the reaction since chlorate(I) (active ion in bleach) undergoes disproportionation disproportionation if heated:  –   –   –  3ClO (aq) 2Cl (aq) + ClO3 (aq) (1)Give one piece of everyday evidence that reaction 2NaCl + 2H 2O  2NaOH + H2 + Cl2 can’t occur without electrolysis (1)Salt water does not evolve Cl 2 (2)Sug (2)Sugges gestt why why a cataly catalyst st maybe maybe in in the the form form of a gauze gauze or or mesh mesh (2)Inc (2)Increa reased sed surfac surfacee area/ area/mor moree activ activee sites sites (3)(i)Explain (3)(i)Explain how the process results in the formation of NaOH in the cathode compartment (i)H+ removed or OH – formed • Na+ ions migrate to cathode/through the diaphragm

(ii)Forms hydroxides/ppts/compounds hydroxides/ppts/compounds which block the diaphragm/the cell (ii)Suggest why the brine must be purified to remove Ca and Mg ions (iii)In modern processes, diaphragm diaphragm replaced by membrane which is ion-selective. ion-selective. It will allow Na ions to pass through but will not allow Cl ions through. Suggest advantage of such such a process (iii)Purer product/faster production/no NaCl present in product (4)(i)In production of NaOH why an electrolytic process rather than one where metal is first produced and then reacted with water? (ii)Sodium has to be made electrolytically electrolytically anyway or reaction reaction violent/too exothermic or 2 stages is more expensive to melt NaCl (ii)In production of NaOH why a titanium anode, rather than a steel one? (ii)Steel is more reactive than titanium/titanium titanium/titanium less reactive steel reacts with the chlorine