M1.(a) Must be 1 decimal place 1

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1 M.(a) 64.0 Must be decimal place 7.(%) (= / Qa) Consequential on their (a) Ignore precision but must be to at least 2 sig fig. (i.e. accept 7 or 7.07) (c) (i) Absorption depends on (proportional to) path length / distance travelled through solution Do not allow size. (ii) To select the colour / frequency / wavelength that is (most strongly) absorbed (by the sample) Allow the filter is chosen to complement the colour of the solution (iii) Quicker to analyse extracted samples than by titration / uses smaller volumes of solution [5] M2.(a) ΔE = hv Allow = hf v = ΔE / h = / = s / Hz Allow s / Hz Answer must be in the range: (One colour of) light is absorbed (to excite the electron) Page 2

2 If light emitted, CE = 0 The remaining colour / frequency / wavelength / energy is transmitted (through the solution) Allow light reflected is the colour that we see. (c) Bigger Blue light would be absorbed OR light that has greater energy than red light would be absorbed OR higher frequency (of light absorbed / blue light) leads to higher ΔE Can only score M2 if M is correct. (d) Any three from: (Identity of the) metal Charge (on the metal) / oxidation state / charge on complex (Identity of the) ligands Co-ordination number / number of ligands Shape 3 max [9] M3.(a) Orange dichromate Allow max 2 for three correct colours not identified to species but in correct order Changes to purple / green / ruby / red-violet / violet Chromium(III) (Note green complex can be [Cr(H 2O) 5Cl] 2+ etc) Do not allow green with another colour Page 3

3 That changes further to blue Chromium(II) Allow max for two correct colours not identified but in correct order [Cr 2O 7] H + + 3Zn 2Cr Zn H 2O 2Cr 3+ + Zn 2Cr 2+ + Zn 2+ / Ignore any further reduction of Cr 2+ [Cr 2O 7] H + + 4Zn 2Cr Zn H 2O Ignore additional steps e.g. formation of CrO 4 2- Green precipitate (Dissolves to form a) green solution Solution can be implied if dissolvesߣstated [Cr(H 2O) 6] OH Cr(H 2O) 3(OH) 3 + 3H 2O Penalise Cr(OH) 3 once only Cr(H 2O) 3(OH) 3 + 3OH [Cr(OH) 6] H 2O Allow [Cr(H 2O) 6] OH [Cr(OH) 6] H 2O Allow formation of [Cr(H 2O) 2(OH) 4] and [Cr(H 2O)(OH) 5] 2- in balanced equations Ignore state symbols, mark independently (c) (ligand) substitution / replacement / exchange Allow nucleophilic substitution Page 4

4 The energy levels/gaps of the d electrons are different (for each complex) Ignore any reference to emission of light So a different wavelength/frequency/colour/energy of light is absorbed (when d electrons are excited) OR light is absorbed and a different wavelength/frequency/colour/energy (of light) is transmitted/reflected (d) E O 2 (/ H 2O) > E Cr 3+ (/ Cr 2+ ) / e.m.f =.67 V Allow E(cell) =.67 So Cr 2+ ions are oxidised by oxygen/air Allow any equation of the form: Cr 2+ + O 2 Cr 3+ With [Cr(H 2O) 6] 2+ get CrCO 3 If named must be chromium(ii) carbonate with [Cr(H 2O) 6] 3+ get Cr(H 2O) 3(OH) 3 / Cr(OH) 3 Allow 0 to 3 waters in the complex and CO 2 Can score M3, M4, M5 in equations even if unbalanced Cr(III) differs from Cr(II) because it is acidic / forms H + ions because Cr 3+ ion polarises water Page 5

5 Ignore charge/size ratio and mass/charge [9] M4.(a)For reactions to 3 must show complex ions as reactants and products Take care to look for possible identification on flow chart Reaction ammonia solution W is [Co(NH 3) 6] 2+ [Co(H 2O) 6] NH 3 [Co(NH 3) 6] H 2O Correct equation scores all 3 marks Reaction 2 Allow oxygen, Do not allow air H 2O 2 X is [Co(NH 3) 6] 3+ 2[Co(NH 3) 6] 2+ + H 2O 2 2[Co(NH 3) 6] OH Allow 2[Co(NH 3) 6] 2+ + ½O 2 + H 2O 2[Co(NH 3) 6] OH Correct equations score all 3 marks Reaction 3 Page 6

6 HCl Do not allow Cl but mark on Y is [CoCl 4] 2- [Co(H 2O) 6] Cl [CoCl 4] H 2O/ Correct equation scores previous mark [Co(H 2O) 6] HCl [CoCl 4] H 2O + 4H + This equation scores all three marks Reaction 4 Na 2CO 3 Or NaOH/NH 3 Do not allow CaCO 3 as a reagent but mark on Z is CoCO 3 Co(OH) 2/Co(H 2O) 4(OH) 2 [Co(H 2O) 6] CO 3 CoCO3 + 6H2O [Co(H2O)6]2+ + 2OH Co(H 2O) 4(OH) 2+ 2H 2O etc Allow waters to stay co-ordinated to Co. This mark also previous mark Or [Co(H 2O) 6] 2+ + Na 2CO 3 CoCO 3 + 6H 2O + 2Na + Allow Co 2+ + CO 3 2- CoCO3 SO ½O2 SO42- Allow multiples The activation energy is lower (for the catalysed route) Or Co 3+ attracts SO 3 2- /Co2+ attracts SO 3 2- /oppositely charged Page 7

7 ions attract ½O 2 + 2Co H + H 2O + 2Co 3+ 2Co 3+ + SO H2O 2Co2+ + SO H+ Allow these equations in either order [6] Page 8