Sri Lankan School30 1. No Mark Schemes available.2.C[1]3.B[1]4.D[1]5.A[1]6.A[1]7.D[1]13.C[1]

15.C[1] 16.(a)A1 (b)D1[2]17.A[1] 18.C[1] 19.(a)D1 (b)B1 (c)C1[3]20.(a)(i)2Mg(NO3)2 2MgO + 4NO2 + O2Correct formulae (1)Balancing (1)ALLOW multiples or equation divided by 2 Second mark on correctspecies only Ignore state symbols even if incorrectALLOWN2O4Extra oxygen molecules on both sides in a balanced equation2 (ii)Stand alone marksMg2+ / Magnesium ion smaller or fewer electron shells / greatercharge density (1)ORMagnesium ion has same charge (as calcium ion) but is smaller (1)Causes more polarisation /distortion of nitrate / anion (electron clouds)/ NO (bond)(1)ORMgO produced has stronger lattice (1)ORproduction of MgO is more exothermic (1)OR reverse argument based on Ca2+2Magnesium / calcium / atoms / molecules (b)2NaNO3 2NaNO2 + O2ALLOW multiples or equation divided by 2 Ignore state symbols even ifincorrectALLOWExtra oxygen molecules on both sides in a balanced equation1 (c)No as.double bond would be shorter (than single bond) / shorter than dative(covalent) bond.ALLOWStructure has double and single bonds (between N and O)Double and single bonds have different lengths1Implication that the single covalent and dative covalent bonds have different lengths(d)(i)Mark independently Goes darker (brown) (1)ALLOWGoes brownerIgnore comments on mixture first becoming paler if volume increasesEquilibrium moves in the endothermic direction (1)OREquilibrium moves left as forward reaction is exothermic (1)For second mark ALLOWEquilibrium moves left to counteract addition of heat / increase intemperature(1)ORReaction removes added heat by moving left (1)2Brown (gas evolved) (ii)Equilibrium moves right (ALLOW forwards) (so NO2 concentrationdecreases) (1)ORReaction reduces pressure (1)As fewer moles / molecules(ALLOW particles) (of gas) on RHS (1)Stand alone marks2 (e)At T2 more molecules/collisions have energy greater than (or equal to) EA (1)This can be shown on the diagram by indicating areas to right of vertical lineEnergy must be at least EA for successful collision / for reaction (1)OR So more collisions have sufficient energy to react (1)Ignore references to the average energy and speed of the molecules2[12] 21.(a)(i)A hydrocarbon (solvent) / volasil / named hydrocarbon solvent /tetrachloromethane Formulae1EthanolAlkenes (ii)Red / brown /orange / amber / yellow Or any combinationNo TE on incorrect / no reagent1(b)(i)Oxidation number of S in H2SO4 = (+)6Oxidation number of S in SO2 = (+)4 (1)Oxidation number had decreased (1)ALLOWS has gained electrons for second markSecond mark stands alone provided oxidation numbers havedecreased, even if calculated wrongly2Just S has gained electrons without calculating oxidation numbers (ii)Black / (shiny) grey solid (1)Purple / violet / pink vapour / fumes (1)Smell of (bad) eggs (1)Yellow solid (1)ALLOWBrown liquid (1)Any two2Purple solid (iii)Oxidation number of S has reduced more / to 2 (in H2S) (1)OROxidation number of S is lower in H2S (than in SO2)If ON of S in H2S is calculated it must be correct1 (c)People can choose whether to take extra fluorideALLOWFluoride is not released into the environment1Fluoride can be monitored[8] 30.D[1]

31.C[1]

32.A[1]33.B[1]35.(a)(i)Use of heat (1)To break down (a reactant)/one reactant into more than one product (1)2(ii)CaCO3(s) CaO(s) + CO2(g)Allow correct multiples1 (iii)Group 2 carbonates are more (thermally) stable as you go down thegroup (1)as the cations get bigger/charge density gets less/cation has more shells (1)So have less of a polarising effect/distortion on the carbonate(ion)/less of a weakening effect on CO (1)2nd and 3rd marks cq on first3Metal gets bigger/element gets biggerCarbonate molecule (b)(i)orange1YellowAny colour in conjunction with orange (ii)(18.0/1000 0.100) = 1.8 103 /0.0018/2 103/0.002IGNORE sf and units even if incorrect1 (iii)(50/1000 0.100) = 5 103 (1)[If candidate fails to divide by 1000 in both (b)(ii) and b(iii) penaliseonly once]Moles HCl reacted = 3.2 103 (can get first mark here if 5 103not shown above)So moles CaO = 1.6 103 (1)IGNORE sfAllow TE from b (ii)2(iv)Mass CaO = (1.6 103 56.1) = 0.0898 g (1)% purity = 0.0898/0.121 100 = 74.2% (1)ORAllow % calculated in terms of moles e.g moles of CaO shouldbe 0.121 56.1 = 0.0021568 (mol) (1)% purity = 0.0016/0.0021568 = 74.2% (1)Accept= (1.6 x 103 56)= 0.0896 g (1)% purity = 0.0896/0.121 100 = 74.0% (1)Allow TE of incorrect moles of CaO from (b)(iii)Allow TE from incorrect mass of CaO if answer is 100%0.09 g and 74.4% is 1 out of 2 (rounding too soon)2Any % purity without 3 sf for second mark (c)(i)(Clean) nichrome/platinum wire/ceramic rod/silica/nickel/chrome rod (1)(In conc.) HCl/HCl(aq)/dilute HCl (1)Heat/place in (blue Bunsen) flame (1)3Metal loop/inoculating loop/glass rod/silver/spatulaPlace in yellow Bunsen flame/burn (ii)Barium/Ba/Ba2+1[16] 38.A[1] 39.C[1] 40.D[1] 41.C[1] 42.B[1] 43.B[1] 44.C[1] 45.D[1] 46.A[1]47.A[1] 48.A[1] 49.(a)(i)Procedure: Only one titration carried out/ no check onaccuracy of titrationOR1000 cm3 volume to large to fit in titration flask (1)Recording: Did not record burette readings to 0.05 cm3/1 decimal place / sufficient precision / recordingonly one significant figure in a titration reading (1)2 (ii)4.65 105 / 4.7 105 / 0.0000465 / 0.000047 (mol)1 (iii)2.3 105 / 0.000023OR candidates answer to (ii) divided by 21 (iv)2.3 105 / 0.000023 mol dm3OR candidates answer to (iii)1 (b)(i)QWCRedox as chlorine removes/gains electrons from the metal(and is reduced) (1)And metal gives/loses electrons to the chlorine (and is oxidised) (1)Redox is essential in order to score both marksThe gain / loss of electrons can be awarded from two ionichalf equations.2 (ii)Chlorine is (highly) toxic/poisonous/irritantOR chlorine has an unpleasant smell (1)1 (iii)Ca(ClO)2 (1)1 (iv)QWCCl is oxidised from +4 (in ClO2) to +5 (in HClO3) (1)and is reduced (from +4) to +1 (in HClO) (1)2(c)QWCAny of the five points below as long as they are logically connectedand use correct scientific terminology plus 1 mark for an equationto a maximum of 6 marks.CFCs are greenhouse gasesbecause their dipole moment changes when they vibrateand so contribute to global warmingdepletion of the ozone layercauses less ozone to absorb UV radiation (from the sun) /increase in UV reaching the earths surfacecauses skin cancer / mutationsCFCs (decompose photolytically to) produce free radicalchlorine atoms/ Cl radicalsRecognition that one Cl radical can cause the destructionof many thousands of ozone molecules / or mention ofchain reactionEquationsCl + O3 ClO + O2ClO + O Cl + O2Either equation or other relevant equation (1)6[17]

51.(a)(i)(pale) green1Accept apple greenAccept yellow(y) greenReject blue green(ii)Crimson1Accept redAccept scarletAccept carmineAccept depth of red colour e.g.Dark redDeep redPale redLight redBright redReject red with any other colour e.g.Brick-redOrange-redYellow-redMagenta (b)BaO(1)= 0.592= 1.1812Accept dividing by 32 scores (0) unless their table is headed by O2, then answer BaO2 scores (1)Correct working leading to answer BaO2 (1)but if this is the case BaO scores (0)Working must be shown and final formula given for 2 marksBaO2 without working 1 mark2Reject any answer dividing by atomic number (0)This leads to Ba2O (c)(i)Ba + 2H2O Ba(OH)2 + H2Ignore state symbols even if they are wrong1Accept multiplesReject equations based on BaO(ii)Gets warmAccept heat producedEffervescence/fizzing/ bubbles/mistAccept bubbles of hydrogenBa sinks/moves up and down /Does not floatGive one mark for observation from each bullet point to max of 23 answers given, one wrong scores (1)3 answers given, two wrong scores zeroIgnore mention of Steam/steamy fumesBa gets smallerBa disappearsGoes cloudy / precipitateGas/hydrogen evolved is not an observation2Reject reference to flameReject meltsDashes about on surface are wrong answers (iii)Red litmus (goes) blue/ () blueandblue litmus unchanged/stays blue/no effect/nothing1[8] 52.(a)(i)4LiNO3 2Li2O + 4NO2 + O2Species (1)Balance (1)Not stand alone conditional on correct species2Accept or fractions/ multiples (ii)2CsNO3 2CsNO2 + O2Correct balanced equation1Accept or fractions/ multiples(b)(i)There must be a comment about both barium andcalcium to score both marksBarium would react to produce a (colourless)/(clear)solution does not give a ppt./ clear (1)Allow Ba and Ca in argumentAccept barium hydroxide dissolvesReject goes colourlessCalcium would go cloudy /give (white) ppt. (1)E.g. Calcium would go cloudy but barium (goes) clear (2)2Reject other colours (ii)Insoluble/ solid/layer / coating of barium sulphateformed (1) allow equn with BaSO4(s)Must say what the coating is since question says useinformation in tableWhich prevents acid getting to surface (of barium) (1)2nd mark conditional on 1st need some idea that asubstance is formed that generates a barrier to further reaction2If candidate uses word ppt must be clear that this is on the surface of the barium or causes interferenceReject BaSO4 unreactiveReject barium disappearsAny reference that implies barium all used up or was a very small piece or acid not in excess or reaction over scores zeroReject references to other layers such as oxide/hydroxide (c)Insoluble (1)1 (d)Ca(s) + 2H+(aq) Ca2+(aq) + H2(g)1 mark for equation1 mark for state symbols2Accept state symbol mark for correct molecular equationCa(s) + 2HCl(aq) CaCl2(aq) + H2 (g) scores (1)[10]53.(a)Any statement that means the number gets lessEgDecrease (in oxidation number of an element)Reduction of ONLowering of ONON becomes more negativeON becomes less positive1Reject just Gain of electrons (b)(i)2NaBr + 3H2SO4 2 NaHSO4 + SO2 + Br2 + 2H2OOR2NaBr + 3H2SO4 2 NaHSO4 + SO2 + Br2 + 2H2OOR2NaBr + 3H2SO4 2 NaHSO4 + 1SO2 + 1Br2 + 2H2O1 (ii)H2SO4 : +6 / 6 / VI / 6+HSO4: +6 / 6/ VI / 6+SO2 : +4/4/IV / 4+H2S : 2 / II / 2All four correct 2 marksAny 3 correct 1 mark2Reject superscript + e.g S6+ (iii)Change in ON of S increases down (halide) group (1)Link all three changes to actual numbers with halide (1)Consequential on answers to part(ii)2Correct answer referring to only two halides scores 1 markIf ref to halogens lose second mark[6]54.(i)Enthalpy change when 1 mol of gaseous ions (1)Accept energy or heatReject any implication of an endothermic processe.g. energy requiredReject .1 mol of gaseous atomsis dissolved such that further dilution causes nofurther heat change (1)Accept added to water/reacts with water instead of dissolvedReject just hydratedReject just completely hydratedIGNORE standard conditionsAccept is dissolved to form an infinitely dilute solutionORIs dissolved in a large/excess/infinite amount of waterMark each aspect independently2(ii)EITHERHSOLN = (HLE + HHYD) (1)Expression quoted or correctly used in at least one ofthe calculations belowAccept answer only with no working (1)HSOLN MgSO4 = (2874) + (1920)= +954 (kJ mol1) (1)HSOLN = BaSO4 = (2374) + (1360)= +1014 (kJ mol1) (1)Accept answer only with no working (1)Enthalpy of solution of MgSO4 less endothermic/moreexothermic/more negative than for BaSO4, so MgSO4more soluble than BaSO4 (or reverse argument) (1)Reject just solubility/Hsoln depends on a balance between lattice and hydration energiesOR(both) lattice energies and hydration enthalpiesdecrease from MgSO4 to BaSO4 (or down group) (1)Accept The hydration energies decrease faster..Reject ()500 and ()560 stated without further explanation(but) lattice energies change less (1)HSOLN = (HLE + HHYD) (1) stated in words or symbolsReject just solubility/Hsolution depends on a balance between lattice and hydration energiesso Hsoln less exothermic/more endothermic/morepositive for BaSO4 so less solubleOR so Hsoln more exothermic/more negative/lessendothermic for MgSO4 so MgSO4 more soluble (1)4[6] 55.(a)(i)Br2(aq) + H2O(l) 2H+(aq) + Br(aq) + BrO(aq)formulae (1)balancing (ignore state symbols) (1)2Accept H+(aq) + Br(aq) + HBrO(aq)/ BrOHH+(aq) + BrO(aq) + HBr (aq)If HBr + HBrO, H+ must be crossed out(ii)reaction is reversible/equilibrium (reaction)can go backward and forward/can go both ways/occurs inboth directions1Accept reversable (1) (iii)bromine has been both oxidised and reduced (1)must mention bromine (Br/Br2 for first mark)from 0 to +1 and 1 (1)2Accept Br oxidation number both increased and decreased /goes up and downReject bromine goes to +1 and 1must show from 0Reject arguments based on OILRIGIncorrect identification of ox/red i.e. ox is 0 1 (iv)Cl2(g) + 2Br(aq) 2Cl(aq) + Br2(aq)formulae (1)balancing and state symbols (1)second mark dependent on first unless correct but non ionicequation givenCl2(g) + 2KBr(aq) 2KCl(aq) + Br2(aq)2Accept Br2(l)Accept multiplesReject Cl2(aq)Reject Br2 (g) Br(aq) (b)(i)Sulphur from +4 to +6 /4+ to 6 + /4 to 6 (1)Bromine from 0 to 1 (1)Accept name or symbol (S or Br or Br2)2Accept oxidation and reduction transposed but correct numbers 1 ( out of 2)Elements correctly identified but incorrect numbers1 (out of 2)Accept sulfur, sulpher, sulfer (ii)Br2 + 2H2O + SO2 4H+ + 2Br + SO421Accept multiples[10]56.(a)(i)Ba + 2H2O Ba(OH)2 + H2IGNORE state symbols1Accept multiplesReject Ba + H2O BaO + H2 (ii)NaCl + H2SO4 NaHSO4 + HClOR2NaCl + H2SO4 Na2SO4 + 2HClIGNORE state symbols1Accept multiplesReject HNaSO4 (b)(i)Green/pale green/apple green1Accept yellow-greenReject any mention of blue e.g. blue green OR any other colour (ii)Red1Accept deep/dark red / carmine/crimson /scarletReject lilacReject any mention of lilac e.g. lilac-red OR any other colour (c)Electrons (absorb heat/energy) and are promoted to higher energylevels (1)as they drop back/down (1)Emit radiation (of characteristic colour)OR emit light (1)3Accept excited/go instead of promotedAccept orbitals/shells instead of energy levelsReject if any reference to absorption spectrae.g. light absorbed (0)Reject (produce) colours (0)

(d)Percentage oxygen (= 45.1)(1) Ar (1)Empirical formula = KO2(1)e.g.Percentage of oxygen = 45.1(1)KO54.945.1(1)39161.412.82KO2 (1)3Accept use of atomic numbers 2 maxAccept use of O2 Mr ~ 32 but only if give formula KO2 (for 3 marks)Reject mole calculation then inverted, no consequential marking on formula[10] 57.(a)H2SO4 + NaCl NaHSO4 + HCl/H2SO4 + 2NaCl Na2SO4 + 2HCl2Either versionState symbols (Ignore these)MultiplesH2SO4 + NaCl NaSO4 + H2 Cl (0)Correct formulae (1) Balanced (1)Second mark depends on first being correct4 correct formulae with an additional existing moleculeeg H2, SO2 Max 1 (b)(i)Sulphur: from +6 to +4 (1)Bromine: from 1 to 0 (1)2Accept sign after value,Roman numeralsIncorrect signs(ii)Increase in ox number of bromine = 2 1 / 2 (1)One S decreases in ox number by 2 (1)Must be clear that one S atom is unchanged/only one Schanges for second mark.[Look for oxidation no. written under elements in equation]2Accept increase in oxidation number of Br = decrease in oxidation number of S, without specifying values (1)Reject explanations in terms of electrons (c)(i)Going down groupNumber of electrons increases (1)Accept reverse argument going up groupReject arguments based on quantum shells.So Van der Waals force (between molecules) increases (1)Ignore comments on radius of atom2Reject vdw for Van der Waals (ii)Boiling point between 200 and 300 (K) (1)73 to +27 if value quoted in CHydrogen bonding is present (1)Stronger forces between molecules /stronger intermolecularforces (than in other hydrogen halides.) (1)3Accept B pt 155 175(K) with explanation that there are fewer electrons in HF for maximum 1 mark.Accept boiling point in correct range, with comment on much stronger dipole in HF and stronger intermolecular forces (2)[11] 58.(i)Red/brick-red/orange-red (1)NOT Orange on its ownYellow (1)2ALLOW orange (ii)electrons promoted (by heat/flame to a higher level) (1)NOT electrons excitedfall back down/return (1)emit light (1)3[5]62.(a)Ca + 2H2O Ca(OH)2 + H2formula Ca(OH)2 (1)correct equation (1)ignore state symbolsincorrect symbol for calcium, penalise onceAny one from each line (max 2)Gets warm (1)Effervescence / fizzing/bubbles / mist/steam / bobs up & down (1)white ppt / white solid / cloudy / milky / white suspension (1)Ca disappears / gets smaller / dissolves (1)If more than two answers given and one or more wrong max 14 (b)Increases1 (c)(i)24.4 / 40 = 0.6117.1 / 14 = 1.2258.5 / 16 = 3.66if rounded to 1dp, must be correct(0.61 / 0.61) = 1(1.22 / 0.61) = 2(3.66 / 0.61) = 6(Therefore it is CaN2O6)penalise use of atomic number once OR first correct % (1), next two correct (1) e.g.(1)(1)2(ii)Cation/group 2 ion (radius) larger (1)same charge stated or shown (1)[lower charge density/charge:size ratio of ion award (1)of first two marks]polarises / distortsanion / nitrate / negative ion (1)NOT just polarisingALLOWLE of oxide and nitrate decrease down the group (1)LE of oxide decreases faster (1)So nitrate becomes more stable relative to oxide (1)3[10] 63.(a)Substance which accepts/gains electrons (from another species) /which removes electrons1 (b)(i)Fluorine / F2ACCEPT Flourine / Flurine / FlorineNOT F or Fl21 (ii)(Red / brown / orange (or combination) and / or volatile) liquid1 (c)Red/brown / orange or combinations of these coloursNOT yellow or any other coloursSteamy / misty (fumes)NOT whiteIf incorrect product linked to observation (0)1 (d)+1 / 1+ / +I / I+ / I+5 / 5+/ +V / V+ / V+ can be sub or superscript2(e)2OH + Cl2 Cl + OCl + H2OOR6OH + 3Cl2 5Cl + ClO3 + 3H2OChlorine species ie Cl2 , Cl , OCl or Cl2 , Cl, ClO3 (1)ALLOW Cl2, NaCl, NaOCl / NaClO3Balancing (1)Correct ionic equation only, spectator ions (0)Explanation in terms of oxidation number e.g. chlorine(allow Cl2 / Cl) is oxidised 0 to +1 (1) and is reducedfrom 0 to 1 (1)ALLOW If chlorine goes from 0 to +1 and 0 to 1 (1 out of 2)Consequential on the disproportionation equation4 (f)(i)Cl(g) + e Cl (g)species (1)state symbols (1) only for correct equation andX(g) + e X (g) max 12 (ii)(ion and electron) both negatively chargedOR electron added to a negative ion(energy required to overcome) repulsion2[14] 65.(a)3OCl 2Cl + ClO3 (1)chlorine (in OCl) is (simultaneously) oxidised from +1 to +5 (1)and reduced from +1 to 1 (1)If only oxidation numbers given max 1 (out of 2)If oxidation numbers omitted max 1 (out of 2)3 (b)(i)blue / black to colourless1(ii)no. moles used = 12.5 0. 1 / 1000 = 1. 25 103 (1)no. moles I2 = 1.25 103 / 2 = 6.25 104 (1)no. moles ClO = no. moles 12 (1)no. moles ClO in original 10 cm3 = 10 6.25 104 = 6.25 103 (1)no. moles ClO in 1 dm3 = 100 6.25 103 (1) = 0.6255 (iii)mass Cl2 = 0.625 71= 44.4 (g)mark consequentially on (ii)must be 3s.f. in final answer1 (c)Cl2 is the stronger oxidising agent because Cl2 oxidises S from(+)2 to (+)6 (1)but l2 oxidises S from (+)2 to (+)2.50 (1)2 QWC(d)O2 oxidises KI / iodide to l2. or balanced equation (1)ll2 reacts with starch / paper to give blue / black (1)2[14]

67.O2 + H2O 2OHIGNORE state symbolsALLOW if Mg2+ shown on both sides1[1] 68.(a)Gas / ggreen/pale green/yellow (1)Liquid / lbrown/red-brown / orange / red-orangeNOT red alone (1)Solid / s(dark) grey ALLOW blackNOT purple (1)3IGNORE shiny / silverAny combination of allowed colours (b)(i)KCl + H2SO4 KHSO4 + HClOR2KCl + H2SO4 K2SO4 + 2HClALLOW multiplesIGNORE state symbols1(ii)Oxidation numbers: -1 (+) 6 / (+) VI 0 (+) 4 / (+) IVCharge can be either side of number(1) mark for any two correct oxidation numbers (2)Oxidising Agent: (concentrated) H2SO4 (1)NOT diluteOxidation no. of bromine / bromide / Br changes from -1 to 0 / risesOROxidation number of sulphur/ S changes from +6 to +4 / falls (1)ALLOW T.E. for incorrect oxidation numbers in the correct direction4onlyIGNORE electrons if in correct direction4th mark not awarded if incorrect oxidising agent given EXCEPT sulphur[8] 69.(a)(i)% of oxygen = 45.1% (1)54.9/39 = 1.41 and 45.1/16 = 2.82 (1)1.41/1.41 = 1 and 2.82/1.41 = 2 (hence KO2) / 1.41 : 2.82 1 : (1)2MUST have some working3Correct inductive reasoning (3)(ii)-0.5 / / -.51 (b)KNO3 because K+ / potassium ion has larger radius / is larger - ion essential (1)but same charge - stated or K+ and Li+ given[lower charge density scores 1 out of the first two marks]Charge density on its own (1) UNLESS term is explained (2)polarises/distorts nitrate/negative ion/anion less (1)OR weakens bonds in nitrate lessNOT weakens ionic bondIf LiNO3 more stable (0)3[4]

72.Diagram showing correct covalent and hydrogen bonds (1)Linear around H and water shown V shaped (1)+ H and O (1)due to difference in electronegativities / because both atoms small /description of involvement of lone pair (1)4[4]73.(a)(i) OR all dots/crossesshared pair (1)correct outer shell (1) consequential on 1stmark2(ii)Because HI has more electrons (1) NOT iodine/iodideNOT because atoms are bigger/heavierit has stronger/larger induced dipole / vdW / London / dispersionforces (1)more energy is required to separate the molecules/break/overcome vdWforces (1)3(b)(i)HI + H2O H3O+ + IIGNORE state symbolsNOT HI H+(aq)+I(aq)1(ii)It forms (hydrated) hydrogen/hydroxonium ionsAny reference to H+ will sufficeNOT proton donor1(c)(i)CaO(s) + 2HCl(aq) CaCl2(aq) + H2O(l)equation (1)state symbols consequential on correct equation (1)2(ii)Because the surface of the calcium oxide gets coated with insoluble/sparingly soluble / impermeable calcium sulphateA protective layer of . impermeable and coated1[10]74.Magnesium or beryllium1[1]75.(a)2p63s23p63d104s2(1) 4p65s2(1)2(b)(i)Sr(g) Sr+(g) + eFormulae (1)State symbols (1)2(ii)ALL increasing (1)Jump between second and third larger than between any other pair (1)2(c)Provide red colour1(d)(i)Sr2+1(ii)Sr(OH)21(e)(i)Sr(s) + 2H2O(I) Sr(OH)2(aq or s) + H2(g)Formula, H2 and balancing (1)State symbols (1)2(ii)Sr(OH)2(s) + 2HCl(aq) SrCl2(aq) + 2H2O(I)Formulae and balancing (1)State symbols (1)2(f)Any number from 8 to 12 inclusive1[14]76.ALLOW multiples in (i), (ii) and (iii) and (c)(a)(i)Ca Ca 2+ + 2e / Ca 2e Ca 2+1(ii)2H2O + 2e H2 + 2OH1(iii)Ca + 2H2O Ca2+ + H2 + 2OHOr Ca(OH)2 + H2NOT consequential on (i) and (ii)1(iv)(Vigorous) bubbles/fizzes/effervesces (1)(white) ppt./suspension / cloudy / milky (1)IGNORE gas evolved/ hydrogen produced/ namesIGNORE calcium dissolves/gets smallerIf flame described 1 max2(b)Increases1(c)2Na + Cl2 2NaClspecies (1)balancing (1) dependent on 1st mark2[8]77.(a)Iodine/ I2 OR astatine / At21Bromine/Br21Chlorine / C12 OR fluorine/F2If halides given max 2If symbols for atoms given max 2If symbols for ions given 01(b)(i)Ions produced (1)to which H2O bonds /become hydrated (1)2(ii)H+ formed (in solution) / H3O+1(c)hydrogen bonding in HF (1) - stand alonestronger than vdW/dipole-dipole/dispersion forces in HI (1) - must be anidentified intermolecular force NOT HI does not have hydrogen bonding2(d)+1 , +5 / 1+, 5+ / I, V (2)1, 5(1)1, 5(0)Superscript pluses penalised once eg Cl+, C15+ (1)BUT Cl+, Cl3+ (0) ie two errors2[10]

83.(a)(i)+7/7+ /VII1(ii)+7/7+ /VII1(b)(i)Sn2+ Sn4+ + 2e() OR Sn2+ 2e() Sn4+(1)I2 + 2e() 21 (1)2

(ii)Sn2+ + I2 Sn4+ + 2IIGNORE state symbols1[5]88.(a)% oxygen 100 (31.84 + 28.98) = 39.18 (1)KClO31.84/3928.98/35.539.18/16Divide by Ar (1)0.81640.81632.448Divide by smallestAlternative multiply by Ar + SUM (1) Calc % (1) 39.18 for 0 (1)3(b)Ratio of moles or mass (1)Moles of A or relative mass of A (1) 24 or volume of O2 (1) (not stand alone)E.g.2 moles of A gives 3 mols of oxygen (1) 1.0g of A 1.00/122.5 moles of Atherefore 1.00 3/122.5 2 moles of oxygenvolume of oxygen = 1.00 3 24 / 122.5 2 = 0.294 dm3OR1.00g of A gives 0.3918 g of oxygen (1)0.3918 g of oxygen = 0.03918/32 moles of oxygen = 0.0122 moles (1)0.0122 moles of oxygen = 0.0122 24 dm3 of O = 0.293 dm3 (1)2-4 significant figure in answer allowed3[6]89.(a)Br or bromide [care clearly bromide ion] (1)1(b)A colourless solution / a greenish-yellow gas / greenish-yellow solution (1)Turn to a brown/ red-brown solution/ gives a black or grey solid (1)NOT red / yellow / orangeIf solution not indicated but colourless brown (1)If neither state is indicated and colourless black (0)2(c)(i)(Simultaneous) oxidation and reduction of same species (in the samereaction)NOT atom, element, particle, substance, ion1(ii)Selects C (1) - conditional on an attempt at an explanation3 chlorine oxidation numbers +1, +5, 1 (1)Linkage +1 to +5 identified as oxidation AND +1 to 1 identified asreduction (1)3[7]90.(a)(i)Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)1 mark equation ionic equation must include spectator ions1 mark state symbols2(ii)In Ca valence electrons further away from nucleus / less attractionof nucleus on valence electrons / more shielding (1)Lower IE / loses outer electrons more easily (therefore faster reaction) (1)2(iii)Calcium sulphate (1)Forms an insoluble / protective layer (1) - NOT free standing ifincorrect compound2(b)(i)2KNO3 2KNO2 + O2 (1)2Ca(NO3)2 2CaO + 4NO2 + O21 for species1 for balance2(ii)Calcium nitrate less (thermally) stable / decomposes more easily thanpotassium nitrate (1) dependent on attempt at explanationCalcium ion smaller (1)} (1) for greater charge densityCalcium ion has double charge (1)}Therefore greater polarising power / greater polarisation of nitrate (1)Bonds in nitrate more easily broken / oxide ion / oxygen atom moreattracted (1)5[14]93.(a)An element with its highest energy electron in a p orbital (1)1(b)(i)Colour brown (1)State: liquid (1)2(ii)The solution goes (from colourless to) dark brown / black solidproduced (1)1(c)(i)Br2 + 2e- 2Br (1) or this1(ii)Fe2+ Fe3+ + e- (1)1(iii)Br2 + 2Fe2+ 2Br- + 2Fe3+ (1)1or this(d)(i)Br2 + 2NaOH NaBr + NaOBr + H2O (2)1 mark for correct bromine products2Ionic equation acceptable(ii)Disproportionation (1)1(e)(i)KBr -1 (1) KBrO3 +5 (1) Br2 0(1)3(ii)Oxidising agent: KBrO3 (1)Oxidation number of Br in KBrO3 goes down (1)2

[15]96.(a)Bromine liquid (1)Iodine solid (1)2(b)AgNO3 (aq): yellow ppt / solid / suspension withNal (1)Cream / pale yellow / off white / ivoryppt / solid / suspension with NaBr (1)Not cloudy not white.Add ammonia solution :ppt. insoluble / stays the same. Nal (1)ppt. (partially) soluble NaBr (1)4If says dilute ammonia must say partially soluble for AgBr.If says conc ammonia must say soluble for AgBr.[6]97.(a)(i)2Ca + O2 2CaO (1)1(ii)Na2O + H2O 2NaOH (1)1(iii)Na2O + 2HCl 2NaCl + H2OSpecies (1) Balancing (1)2(b)(Thermal stability) increases (1) (with someattempt at a reason)(cat)ion size increases / (cat)ion charge density decreases (1)polarises or distorts carbonate ion / anion /electron cloud less. (1)3[7]100.(a)(i)NaCl + H2SO4 NaHSO4 + HCl (1)or2NaCl + H2SO4 Na2SO4 + 2HCl (1)1(b)(i)add silver nitrate (solution) / correct formula AgN03 (aq) (1)white ppt /solid (1)soluble in dilute ammonia /ammonia solution (1)oradd lead nitrate/ethanoate (solution) (1)white ppt. (1)soluble in hot water (1)Any feasible correct chemical method can score the marks here3(ii)dissociates /reacts/lionises/changes into ions (as it dissolves) (1)forming H+ ions / H3O+ ions/ donates a proton to water. This makes the solution an acid (1)2(i)damp litmus paper (1) bleached (1)ordamp starch-iodide paper (1) goes blue (1)Displacement acceptable2(ii)[+4] [-1] (1)[+2] [-1] [0] (1)positive charge not essential2(d)(hydrogen) iodide is more easily oxidized / loses electrons moreeasily than (hydrogen) chloride (1)because larger (than chloride) (1)Could argue from the reducing power of the iodide / chloridefor the first mark2[12]102.(a)(i)Ca brick red or orange red, Ba (apple) green (1) each2(ii)electrons excited / promoted (1)fall to lower energy level / orbital (1)give out energy in the visible region / in form of light (1)3(b)2Ba(NO3)2 2BaO + 4NO2 + O2 (2)species (1) balance (1)2

(c)(i)ability (of a cation) to distort / change shape of (1)the electron cloud around an anion (1)2(ii)Size /radius /ionic radius (1) charge (1)2(iii)Mg2+ / magnesium ion smaller than Ba2+/ barium ionorMg2+ has higher change density (1)Polarising power increases/ Mg2+ able to polarise the nitrateion more effectively than Ba2+ (1)this weakens the bonds in the nitrate / bonds in nitrate moreeasily broken (1)3[14]103.(a)B (1)1(b)Limewater turns milky CO2 (1)MgCO3 decomposes on heating to CO2 label correct / equation (1)2(c)Substance on wire in flame (1) not burn or heat (in test tube)(Pale) green flame for barium (1)No colour for magnesium (1)oradd dilute sulphuric acid (1)barium hydroxide does not dissolve (1)magnesium hydroxide dissolves / forms colourless solution (1)orValid chemical test3(d)(brown gas is) nitrogen dioxide (1)(gas relights a glowing splint) oxygen (1)2Mg(NO3)2 2MgO + 4NO2 + O2species (1) balance (1)4[10]105.(a)(i)LiCl red/scarlet/crimson/carmine red (1)NaBr orange/yellow (1)KI lilac/purple/mauve/pink/violet/lavender (1)3(ii)Excited electrons (1)Move down energy levels (1)2(b)(i)LiCl - white/steamy fumesNaBr - brown/orange vapour or liquidKl - purple vapour / dark solid or liquid or residue4(ii)LiCl(s) + H2SO4(l) LiHSO4(s) + HCl(g) formulae (1), states (1)or 2LiCl(s) + H2SO4(l) Li2SO4(s) + 2HCl(g) formulae (1), states (1)2[11]106.(a)(i)Loss of electrons1(ii)A substance which gains/removes/accepts electrons1(iii)Chlorine (is stronger oxidising agent)So it can accept electrons from Br/so it can displace Br/ so can oxidise Br2(b)(i)3OCl ClO3 + 2Cl formulae + charges (1), balancing (1)2(ii)Disproportionation1(c)(i)SO2: +4SO42: +62(ii)Oxidised because oxidation number of S becomes more positive/sulphur loses electrons1(iii)Starch/any named non polar solvent: hexane, chloroform, volasilBlue-black/purple2[12]108.(a)formal charge1an atom would have in a compound if ionic1ORnumber of electrons lost or gained1control of / used for bonding1(b)(i)0 +1 1 (ignore everything else)1(ii)One of the chlorines in each molecule (0 to +1) has lostan electron / been oxidised1The other chlorine in the chlorine molecule hasgained an electron / been reduced to 11a simple statement / definition of disproportionationmax 1(c)reacts / changes / dissociates / ionises / HCl donates a proton to the water1H+ (aq) or H3O+ (aq) ions1(d)white precipitate (1) soluble in ammonia. (1) chloride cream ppte (1)slightly soluble in ammonia (1) bromide yellow ppte (1)insoluble in ammonia (1) iodide6if only 3 colours without any mention of ppte max 1 out of 3[13]109.(a)110.(a)(i)2Ca(NO3)2 2CaO + 4NO2 + O2formulae correct (1) balance (1). Ignore any state symbols.The balance mark is not standalone.2(ii)steam / fizzing sound / crumbles (1)solid swells up / milky liquid produced / comment about sparingly soluble substance (1)CaO + H2O Ca(OH)2 (1) ignore any state symbols3(iii)less (1)1

(iv)(Cat)ion size increases down the Group / charge density decreases (1)(not atom size)The polarizing power of the cation decreases down the Group (1).The less polarized the anion is by the cation the more difficult the nitrate is to decompose (1).Polarisation mark could come from the less the electron cloud is distortedortrend in cation size (1)comparison of the lattice energies of the nitrate and the oxide (1)balance in favour of oxide at top of groupand the nitrate at the bottom (1)3(b)(i)same number of particles in a smaller volume / gas density increased (1)1(ii)comment related to the number of molecules on each side to explain a shift to l.h.s. (1) (not just due to Le Chatelier)so at higher pressure equilibrium moves to favour N2O4 (1)2(iii)Kp = p(NO2)2p(N2O4)There must be some symbolism for pressure, and no [ ]1(iv)(Kp = p(NO2)2 = 48)p(N2O4)p(NO2)2 = 48 0.15 = 7.2 (1)p(NO2) = 2.7 (1) atm (1) accept 2.683 / 2.68 / 2.7Answer and units conditional on (iii).3[16]

6.(a)(i)Mark the two points independently, subject to the constraint inReject columnEffect:(Equilibrium) shifts to the right (1)ALLOW: favours forward reaction / increase the amount of product/ increase the yield (of product)Reason:Exothermic (in forward direction) (1)NOTE: Just (equilibrium) shifts in the exothermic directionscores (1)2Equilibrium shifts to left will score (0) for (a)(i)(ii)First mark:Activation energy for the reaction is too high / (if cooled) moleculeswould not have enough energy to react / few(er) molecules have therequired Ea/more molecules have energy Ea at higher temperaturesORnot (technologically) feasible to cool the gases before they enter theconverter/costly to cool the gases (1)Second mark:(cooling the gases would make) the rate (too) slow /rate is faster if thetemperature is high (so the gases are not cooled) (1)2Cooling the gases decreases the yield (of products) /anincorrect Le Chatelier argument (iii)Mark the two points independently, subject to theconstraint in Reject columnEffect:(Equilibrium) shifts to the rightALLOW: favours forward reaction / increase the amount of product /increase the yield of product (1)Reason:Shifts / moves in the direction of fewer (moles of gas) moleculesALLOW shifts in direction of fewer moles (of gas molecules) (1)IGNORE effect on the rate2Equilibrium shifts to left will score (0) for (a)(iii).... fewer atoms (b)(i)(In NO): +2 / 2+ (1)(In NO3): +5 / 5+ (1)NOTE:(In NO): Just 2AND(In NO3): Just 5 scores (1)2 (ii)NO3 + 4H+ + 3e NO + 2H2OACCEPT multiples2 (iii)Ag Ag+ + e() / Ag e() Ag+ACCEPT multiplesIGNORE state symbols, even if incorrect1Ag + e Ag+(iv)3Ag + NO3 + 4H+ 3Ag+ + NO + 2H2O (2)(1) for multiplication of the silver half-equation by three or cq multiplefrom (b)(ii)(1) for rest of equation correctNOTE: Equation must be completely correct for the second mark.IGNORE state symbols, even if incorrect2if any e are left in the final equation, second mark cannot be scored[13] 16.C[1] 17.(a)A1 (b)C1[2]

20.(a)Starch (solution)1 (b)(i)I2 at start = 1 103 / 0.001 (mol)1 (ii)1.26 103 (mol) thiosulfate (1)6.3(0) 104 / 0.00063 (mol) I2 (1)Correct answer with no working (2)Ignore SF except 1 SF2 (iii)I2 used = (1 103 - 6.30 104) = 3.70 104 (mol) (1)Mol SO2 = mol I2 = 3.70 104 / 0.00037 (mol) (1)Correct answer with no working (1)ALLOW TE from (i) and (ii)Ignore SF except 1 SF2 (iv)Mass SO2 in 100 m3 = (64.1 3.70 104) (1)Mass SO2 in 1 m3 = 64.1 3.70 104 /100 = 237(.2) 10-6 g= 2.37 104g (1)(= 237.2 / 237 / 240 g) units required( within limit)Allow TE from (iii)Ignore SF except 1 SF2 (c)(i)Improved because titration may be repeated /averages could be takenALLOWSmaller titration reading so greater (%) error1 (ii)Larger titration reading (1)So smaller (%)error in titration reading (1)ORSmaller mass of sodium thiosulfate used to make solution (1)So greater %) error in the mass measurement (1)Second mark dependent on correct first or near miss2(iii)Smaller titration reading as more I2 reacts/ less I2 left (1)So greater (%) error in titration reading (1)Second mark dependent on correct first or near miss)ORSmaller (%) error in measuring volume of air (1)2[13]

34.(a)(i)metallic1Reject metal (ii)attraction between ions and delocalised electronsis stronger in lithium (1)With reference to atoms 1 maxas lithium ion is smaller / lithium ion has greater chargedensity/ electrons closer to nucleus (1)2Accept reverse argument(b)(i)2Accept all dots and crossesAccept charges next to element symbolsReject correct electronic structure but wrong or no charges max 1Reject covalent structures = 0 (ii)Electrons are promoted (to higher energy level). (1)Then they fall back to lower levels (they emit lightof particular wavelength). (1)2 (iii)strontium / calcium1Accept rubidium[8] 35.(a)Lithiumcarmine/ red/ magenta/ crimsonAny combination of these or prefaced by deep or darkAccept scarletReject brick-redPotassium: lilacAccept mauve or purpleSodium: yellowAccept orange or yellow-orangeAll three correct 2 marksTwo correct 1 mark2(b)Electrons (absorb heat energy and) are promoted (to higher level) (1)Accept excitedAccept any phrase that implies movement to higher levelIf answer based on absorption spectra scores zeroThey drop back and emit light/radiation (of characteristic colour) (1)2Ignore references to shells, sub-shells, etc.Reject colour or energy (c)(i)LiCl + H2SO4 LiHSO4 + HClIgnore state symbols1Accept multiplesAccept 2LiCl +H2SO4 Li2SO4 +2HCl (iii)NaI + AgNO3 AgI + NaNO3Ignore state symbols and spectator ions1Accept multiplesAccept Ag+ + I AgI[6]

38.(a)3d104s1 and 3d101Accept 4s13d10(b)(i)QWC*the (3)d subshell is full (1)Accept orbitals (it must be plural) for sub-shellReject comments on partially filled sub-shellso no d-d transitions are possibleOR no transitions in the right energy range are possible (1)(and no light is absorbed)Any mention of light emission loses 2nd mark2 (ii)combine the halfreactions to get 2Cu+ Cu2+ + Cu (1)IGNORE state symbolsand show that E for this is (+) 0.37 (V) (and as it is positive it isfeasible) (1)conditional on correct reaction2Reject just > 0.3 (V) (iii)activation energy (for the disproportionation) is highORCu+ is kinetically stable1Reject activation energy for one of the half-equations is too high (c)(i)divides each by atomic mass (1)divides by smallest to obtain Cu2SO6H2 (1)2Division by atomic number scores zero (ii)CuSO4.Cu(OH)2 (2)If formula wrong but sulphate/ SO4 is present scores 1 (out of 2)2Accept Cu2SO4(OH)2Accept Cu2(OH)2SO4Accept (CuOH)2SO4Reject HSO4 instead of SO4 (iii)[Cu(NH3)4(H2O)2]2+1Accept [Cu(NH3)4]2+Reject [Cu(NH3)6]2+ (iv)ligand exchange / ligand substitution1(d)(i)QWC(add aldehyde to 2,4DNP) to obtain precipitate/ppt/solid/crystals (1)recrystallise derivative (1)determine melting temperature of derivative (1)compare with data tables (1) 4th mark conditional on meltingtemperature of a derivative being measured4Reject any identification method based on IR, NMR or mass for last 2 marks (ii)the aldehyde is distilled off as it is formed1Reject any mention of refluxReject just the aldehyde is distilled off (iii)propanoic acid OR CH3CH2COOH OR CH3CH2CO2H1Accept C2H5 for CH3CH2 (iv)No (extra) oxygen presentOR catalyst specific to formation of aldehyde / only lowers Eaof first oxidationOR presence of hydrogen gives reducing conditionsOR copper is not an oxidising agentOR aldehydes rapidly leave catalyst surface1 (v)(At high pressure) all active sites are occupied/fullOR(At higher pressures) rate controlled by availability of sites.1Accept reverse argument for low pressure[20] 39.(a)Ca(NO3)2(s) CaO(s) + 2NO2(g) + O2(g)1Accept doubled up version or multiples (b)(i)Blue1Accept purpleReject green, green-blue(ii)OH / HO/ OH / HO1[3] 40.(a)Red / crimson / carmine1Accept magenta / cherry redReject pink(b)During the flame test promoted/excited electrons return toground state, whereas during ionisation electrons leavepermanently/completelyFlame test: electrons move to higher shells / are excitedthen fall back again / return to lower shells / to ground state(releasing energy), i.e. electrons up then downIonisation: electrons leave (permanently), i.e. electrons outAny false statement regarding energy changes loses the mark, egelectrons are promoted to higher shells releasing energy 1[2] 43.(a)Ca + O2CaO1IGNORE state symbolsALLOW multiples (b)

(1)(1)ALLOW all dots or all crosses for oxide ionMax 1 if no/wrong charges1 mark for two correct chargesCovalent bonding (0)2 (c)(i)Calcium hydroxide1NOT limewater(ii)10 141[5]

44.(a)(i)Add silver nitrate (solution) (1) ACCEPT correct formula(pale) yellow precipitate/solid(1)ORAdd chlorine (solution)/bromine (solution) and hydrocarbon solvent (1)Solvent goes purple/pink/violet (1)2nd mark is dependent on 1st2 (ii)Iodine /I and sulphur / S identified (1) -NOT I2 /I/iodideIodineinitial (+)5final 1(1)Sulphurinitial (+)4final (+)6(1)ACCEPT as roman numeralsACCEPT +/ on either side/sub or superscriptACCEPT as words3 (iii)1 6 = 6,3 +2 = +6ALLOW TE from (ii)OR total change in oxidation number of +6 for S, 6 for IACCEPT justification in terms of electrons1 (b)(i)pipetteALLOW buretteNOT measuring cylinder1 (ii)Starch (solution) (1)blue/dark blue/blue-black/black to colourless (1)ALLOW max 1 if candidate states no indicator needed/self-indicatingwith colour change brown/yellow to colourlessIf no indicator given but correct colour change 1 (out of 2)2 (iii)OR 0.00024 (mol)The mark is for the answer1 (iv)1.2(0) 104 (mol) OR 0.00012 (mol)ALLOW TE from (iii)The mark is for the answer1(v)1.2 104 100 = 0.012(0) (mol dm3)ALLOW TE from (iv)The mark is for the answer1[12]

48.(a)(i)(1s2) 2s22p63s23p11(ii)3rd IE roughly in line with first two in third row(including lines)4th IE well above this line difference between2nd and 3rd + two squares2 (b)(i)Al Al3++ 3eOR 3e on LHSALLOW multiplesIGNORE state symbols1 (ii)O2 + 4e 2O2 (NOT O + 2e O2) (NOT O2 2O2 4e)ALLOW multiplesIGNORE state symbols1 (iii)4Al + 3O2 2AI2O3 ALLOW multiplesStand aloneNOT consequential on bi and iiNOT 4Al3+ + 6O21[6]

51.O2 + H2O 2OHIGNORE state symbolsALLOW if Mg2+ shown on both sides1[1] 52.(a)(i)Cl2(aq) + 2I(aq) 2Cl (aq) + I2(aq / s) OR halved versionEntities (1)Balancing and state symbols (1)2nd mark dependent on 1stunless spectator ions included onboth sides of equation2 (ii)Purple/pink/violet/mauve/lilac OR any combination of these coloursCan be prefixed by deep or darkAny mention of red (0)1 (iii)Orange OR yellow ALLOW red OR brownALLOW any combination of these colours1 (b)(i)iodine in I2 : 0iodine in I : 1 (1)sulphur in SO2 : +4sulphur in SO42 : +6 (1)2 (ii)sulphur dioxide / SO2 ,because of sulphurs increased oxidation number/losing electronsALLOW because sulphur dioxide gains oxygen[both parts needed for the mark]ALLOW reverse argument ie iodine gainselectrons/oxidation number decreases1 (iii)I2(aq) + SO2(aq) + 2H2O 2I(aq) + SO42(aq) + 4H+(aq)ALLOW multiples1 (c)(i)the red colour would interfere with the colour change at theend-pointOR so that the colour of the indicator/the end-point can beseen/determined1 (ii)colourless to (deep/dark) blue / blue-black / blackAny mention of purple (0)1

(iii)moles of iodine = (1)moles of sulphur dioxide = 1.22 105 (1)ALLOW answer equal to or a single digit multiple of answer aboveconcentration of SO2= 1.22 105 (1000) = 4.88 104/0.000488 (mol dm3) (1)25OR 4.9 104/0.00049 (mol dm3)ALLOW TE from answer aboveIGNORE units3 (iv)activated charcoal might react with / adsorb SO2 /(traces of) charcoal might react with I2(thus giving an underestimate of [SO2] in the wine)1[14] 53.(a)(i) (1)cycle with state symbols or as energy level diagram. (1)labels (in symbols, words or numbers) (1)D Hsoln = D Hlat + D Hhyd Ca2+ + 2 D Hhyd OH OR valuesD Hlat = 1650 + 2 (460) (16.2) (1)4 = 2553.8 (ii)Solubility increases down the group (1)(if this is wrong, no marks available in this part)QWCD Hhyd of cation decreases / less exothermic (1)but D Hlatt decreases more (1)therefore D Hsol gets more exothermic / increases (1)4(b)(i)Calcium hydroxide will be less soluble at the higher temperature, (1)(if this is wrong, no marks available in this part)because the reaction is exothermic (left to right) (1)(an increase in temperature will cause a) decrease in the value of K(and (1) hence drive the equilibrium to the left).3 (ii)The solubility will decrease,(if this is wrong, no marks available in this part)because the addition of OH ions will increase [OH] /concentration of OH (1) driving the equilibrium to the left. (1)3 (c)The three gases are:hydrogen bromide) (1)bromine) OR formulae (1)sulphur dioxide) (1)The hydrogen chloride / CaCl2 / chloride evolved is not a strong enoughreducing agent to reduce / cannot reduce the concentrated sulphuric acid (orsulphuric not a strong enough oxidising agent to ) (1)4[18] 54.(a)Any two(Misty) steam / water droplets / condensation (on upper part of the testtube) (1)NOT water vapourNOT white gasBrown gas / fumes / vapour evolved (1)NOT NO2 evolvedNOT fizzingCrystals dissolve (in their own water of crystallisation) /melt /liquefy/form a solution (1)NOT crystals decompose/ get smaller/disappearForms a white solid (1)2(b)Name (1)Test (1) is dependent on correct materiale.g.Water / Steam / H2O (1)(Anhydrous) CuSO4(s) (white) to blueORCoCl2(paper) (blue) to pink/purple (1)NOT damp CoCl2(paper)ORNitrogen dioxide / Nitrogen(IV) oxide / NO2 (1)(moist) litmus/pH paper turns to red/orange/pink (1)NOT pH meterIF nitric acid, allow test with pH paper for 1(out of 2)OROxygen / O2 (1)glowing splint (re)kindles (1)2[4] 55.(a)(i)OH / OH / HO / HOIGNORE brackets1(ii)Ammonia (is a weak base) and is only partially ionised, whereasNaOH(aq) is fully ionised / ammonia has fewer OH ions / lowerOH concentration [or converse]Answer must give a comparison, either explicitly or implicitly e.g.more/less/-er/onlyASSUME it refers to ammonia BUT must still be a comparisonNOT answers in terms of protons being accepted on its ownNOT answers that imply rate e.g. readily1 (b)R Q POR R Q POR R < Q