Question Answer Marks Guidance 1 (a) (+)5 1 ALLOW 5+ OR V OR Cr 5+ 1 (b) For equations, IGNORE any state symbols; ALLOW multiples

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1 Question Answer Marks Guidance 1 (a) (+)5 1 ALLW 5+ R V R Cr 5+ 1 (b) For equations, IGNRE any state symbols; ALLW multiples EXAMPLES N 2 + 3H 2 2NH 3 (allow ) AND Fe/iron oxide Any correct equation for a reaction catalysed by a transition element, compound or ion 2S S 3 (allow ) AND V 2 5 /Pt AND 2C + 2N 2C 2 + N 2 AND Pt/Pd/Rh/Au transition element, compound or ion (by formula or name) 1 Equation for any alkene + H 2 alkane AND Ni/Pt/Pd C 6 H 6 + Cl 2 C 6 H 5 Cl + HCl AND Fe/FeCl 3 /Fe 3+ C 6 H 6 + Br 2 C 6 H 5 Br + HBr AND Fe/FeBr 3 /Fe 3+ 2H 2 2 2H AND Mn 2 1 (c) (i) Donates two electron pairs (to a metal ion) AND forms two coordinate bonds (to a metal ion) NTE: Metal ion not required as Ni 3+ is in the question 1 For other examples, CHECK with TL ALLW lone pairs for electron pairs ALLW dative (covalent) bonds for coordinate bonds TW is only needed once, e.g. Donates two electron pairs to form coordinate bonds Donates electron pairs to form two coordinate bonds 1 (c) (ii) C 3 H 10 N 2 1 ALLW in any order IGNRE structure 1 (c) (iii) MARK INDEPENDENTLY H 2 NCH 2 CH 2 CH 2 NH 2 ALLW correct structural R displayed R skeletal formula R mixture of the above (as long as unambiguous) ALLW H 2 NCH 2 CH(CH 3 )NH 2 R H 2 NCH(CH 2 CH 3 )NH 2 ALLW secondary or tertiary diamines or mixture Each N R each NH 2 R amine group has a lone pair/electron pair R lone pairs shown on N atoms in structure 2 IGNRE complex ion For other examples, CHECK with TL

2 Question Answer Marks Guidance 1 (c) (iv) (c) (v) 3 D diagrams of BTH optical isomers required for the mark In this part, Charge AND Square brackets NT required IGNRE N or attempts to draw structure of bidentate ligand Ni AND Ni 1 ther orientations possible but all follow same principle with 2nd structure being a mirror image of the first

3 Question Answer Marks Guidance 1 (d) Quality of written communication bservation must be linked to the correct reaction REACTINS F AQUEUS Cu REACTIN F Cu 2+ with NaH(aq) Correct balanced equation Cu 2+ (aq) + 2H (aq) Cu(H) 2 (s) state symbols not required bservation blue precipitate/solid 2 FULL ANNTATINS MUST BE USED THRUGHUT ALLW some reactions for Cu 2+ and some for Co 2+ ALLW equilibrium signs in all equations IGNRE any incorrect initial colours IGNRE state symbols IGNRE an incorrect formula for an observation ALLW [Cu(H 2 ) 6 ] H Cu(H) 2 (H 2 ) 4 + 2H 2 ALLW full or hybrid equations, e.g. Cu NaH Cu( H) 2 + 2Na + 2+ [Cu(H 2 ) 6 ] + 2H Cu(H) 2 + 6H NaH Cu(H) 2 + Na 2 S 4 1 (d) 1 (d) REACTIN F Cu 2+ WITH excess NH 3 (aq) Correct balanced equation [Cu(H 2 ) 6 ] NH 3 [Cu(NH 3 ) 4 (H 2 ) 2 ] H 2 bservation deep/dark blue (solution) REACTIN F Cu 2+ WITH HCl(aq) Correct balanced equation [Cu(H 2 ) 6 ] Cl [CuCl 4 ] 2 + 6H 2 bservation yellow (solution) 2 2 CuS ALLW any shade of blue IGNRE initial precipitation of Cu(H) 2 IGNRE [Cu(NH 3 ) 4 ] 2+ ALLW royal blue, ultramarine blue or any blue colour that is clearly darker than for [Cu(H 2 ) 6 ] 2+ D NT ALLW deep blue precipitate for observation IGNRE mention of different concentrations of HCl ALLW CuCl 4 2 i.e. no brackets R Cu(Cl) 4 2 ALLW [Cu(H 2 ) 6 ] HCl [CuCl 4 ] 2 + 6H 2 + 4H + IGNRE Cu Cl CuCl 4 2 ALLW green yellow R yellow green D NT ALLW yellow precipitate for observation

4 Question Answer Marks Guidance 1 (d) Quality of written communication bservation must be linked to the correct reaction REACTINS F AQUEUS Co REACTIN F Co 2+ with NaH(aq) Correct balanced equation Co 2+ (aq) + 2H (aq) Co(H) 2 (s) state symbols not required bservation blue precipitate/solid 2 FULL ANNTATINS MUST BE USED THRUGHUT ALLW some reactions for Cu 2+ and some for Co 2+ ALLW equilibrium signs in all equations IGNRE any incorrect initial colours IGNRE state symbols IGNRE an incorrect formula for an observation ALLW [Co(H 2 ) 6 ] H Co(H) 2 (H 2 ) 4 + 2H 2 ALLW full or hybrid equations, e.g. Co NaH Co( H) 2 + 2Na + 2+ [Co(H 2 ) 6 ] + 2H Co(H) 2 + 6H NaH Co(H) 2 + Na 2 S 4 1 (d) 1 (d) REACTIN F Co 2+ WITH excess NH 3 (aq) Correct balanced equation [Co(H 2 ) 6 ] NH 3 [Co(NH 3 ) 6 ] H 2 bservation brown/yellow (solution) REACTIN F Co 2+ WITH HCl(aq) Correct balanced equation [Co(H 2 ) 6 ] Cl [CoCl 4 ] 2 + 6H 2 bservation blue (solution) 2 2 Total 14 CoS ALLW any shade of blue IGNRE changes in colour over time IGNRE initial precipitation of Co(H) 2 ALLW any shade of brown or yellow D NT ALLW brown/yellow precipitate for observation IGNRE mention of different concentrations of HCl ALLW CoCl 4 2 i.e. no brackets R Co(Cl) 4 2 ALLW [Co(H 2 ) 6 ] HCl [CoCl 4 ] 2 + 6H 2 + 4H + IGNRE Co Cl CoCl 4 2 ALLW any shades of blue D NT ALLW blue precipitate for observation

5 Question Answer Marks Guidance 2 (a) (Transition element) has an ion with an incomplete/partiallyfilled d sub-shell/d-orbital FULL ANNTATINS MUST BE USED ALLW capital D within definition D NT ALLW d shell Scandium/Sc and zinc/zn are not transition elements Electron configurations of ions Sc 3+ AND 1s 2 2s 2 2p 6 3s 2 3p 6 Zn 2+ AND 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 ALLW if NLY Sc and Zn are used to illustrate d block elements that are NT transition elements This can be from anywhere in the overall response in terms of Sc, Sc 3+, Zn, Zn 2+ R incorrect charges, i.e. only Sc +, Sc 2+, Zn + In electron configurations, IF subscripts R caps used, D NT ALLW when first seen but credit subsequently ALLW 4s 0 in electron configurations IGNRE [Ar] IGNRE electron configurations for other Sc and Zn ions ALLW for Sc 3+ : Sc forms a 3+ ion; ALLW Sc +3 ALLW for Zn 2+ : Zn forms a 2+ ion; ALLW Zn +2 Sc 3+ AND d sub-shell empty / d orbital(s) empty Note: Sc 3+ must be the NLY scandium ion shown for this mark Zn 2+ AND d sub-shell full /ALL d-orbitals full Note: Zn 2+ must be the NLY zinc ion shown for this mark 6 ALLW Sc 3+ has no d sub-shell D NT ALLW d sub-shell is incomplete (in definition) D NT ALLW d sub-shell is incomplete (in definition)

6 (b) (i) Donates two electron/lone pairs to a metal ion R Co 3+ D NT ALLW metal (complex contains Co 3+ ) ALLW forms two coordinate bonds/dative covalent/dative bonds as an alternative for donates two electron/lone pairs Two is required for 1st marking point Two can be implied using words such as both or each For metal ion, ALLW transition (metal) ion Electron/lone pair on N R NH 2 (groups) 2 Second mark is for the atom that donates the electron/lone pairs ALLW both marks for a response that communicates the same using N as the focus: e.g. The two N atoms each donate an electron pair to metal ion (b) (ii) [Co(H 2 NCH 2 CH 2 NH 2 ) 2 Cl 2 ] + 1 Square brackets AND + charge required D NT ALLW any charges included within square brackets ALLW [Co(C 2 H 8 N 2 ) 2 Cl 2 ] + R [CoC 4 H 16 N 4 Cl 2 ] + ALLW structural R displayed R skeletal formula R mixture of the above (as long as unambiguous) IGNRE [Co(en) 2 Cl 2 ] + simplifies question Within formula, ALLW.(Cl) 2, (Cl 2 ) ALLW C Within the context of the question, C is Co (b) (iii) 6 1

7 (b) (iv) FULL ANNTATINS MUST BE USED IGNRE charges (anywhere) and labels (even if wrong) Square brackets NT required Must contain 2 out wedges, 2 in wedges and 2 lines in plane of paper R 4 lines, 1 out wedge and 1 in wedge : For bond into paper, ALLW: ALLW following geometry throughout: Note: For each structure, ALL NH 2 groups must be shown AND bonding between Co AND N of NH 2. For H 2 NCH 2 CH 2 NH 2, ALLW C C without Hs and NH 2 NH 2 IF NH 2 shown without Hs, e.g. N N, penalise first time NLY IF ALL 3 isomers are correct, but 2 x Cl AND no Ns, e.g. AWARD 1 mark 3 Co TAKE CARE: structures may be in different orientations. For H 2 NCH 2 CH 2 NH 2, ALLW (connectivity within loop only) NH 2 H 2 N If Cl 2 s are shown instead of Cl, penalise 1st time only

8 (c) (i) 2 /oxygen bonds to Fe 2+ /Fe(II) Fe 2+ /Fe(II) essential for 1st marking point ASSUME that it refers to oxygen ALLW 2 binds to Fe 2+ R 2 donates electron pair to Fe 2+ R 2 is a ligand with Fe 2+ IGNRE 2 reacts with Fe 2+ R 2 is around Fe 2+ (When required,) 2 substituted R 2 released Fe 2+ not required for 2nd marking point (e.g. IGNRE Fe) (c) (ii) [Hb 2(aq)] (K stab = ) [Hb(aq)] [ 2(aq)] ALL Square brackets essential (c) (iii) Both marks require a comparison Stability constant/k stab value with C is greater (than with complex in 2 ) 2 1 ALLW bond to 2 breaks when 2 required R H 2 replaces 2 R vice versa ALLW C 2 replaces 2 R vice versa ALLW 2 bonds/binds reversibly ALLW expression without state symbols (given in question) IGNRE (complex with) C is more stable (Coordinate) bond with C is stronger (than 2 ) R C binds more strongly 2 ALLW bond with C is less likely to break (than 2 ) R C is a stronger ligand (than 2 ) R C has greater affinity for ion/metal/haemoglobin (than 2 ) ALLW C bond formation is irreversible R C is not able to break away Total 18 IGNRE C bonds more easily R C complex forms more easily

9 Question er Marks Guidance 3 (a) 2Fe + 3Cl 2 2FeCl 3 1 ALLW 2Fe + 3Cl 2 Fe 2 Cl 6 ALLW multiples, e.g. Fe + 1½Cl 2 FeCl 3 IGNRE state symbols D NT ALLW 2Fe + 3Cl 2 2Fe Cl (b) Fe H Fe(H) 3 1 IGNRE state symbols ALLW [Fe(H 2 ) 6 ] H Fe(H 2 ) 3 (H) 3 + 3H 2 ALLW [Fe(H 2 ) 6 ] H Fe(H) 3 + 6H 2 (c) (i) 2[Fe(H 2 ) 6 ] 3+ + Zn 2[Fe(H 2 ) 6 ] 2+ + Zn 2+ All chemical species correct (IGNRE e for 1st mark) Balancing with 2 in front of both Fe complex ions 2 IGNRE state symbols For 1 mark, ALLW balancing if (aq) species have been used instead of complex ions: 2Fe 3+ + Zn 2Fe 2+ + Zn 2+ (ii) redox 1 ALLW reduction AND oxidation CARE: possible confusion with (d)(ii) (d) (i) Formula of E as [Fe(CN) 6 ] 3 shown as product in equation 2 Correct balanced equation: [Fe(H 2 ) 6 ] CN [Fe(CN) 6 ] 3 + 6H 2 Notice different charges on complex ions: LHS 3+, RHS 3 state symbols not required ALLW equations with KCN, i.e.: [Fe(H 2 ) 6 ] KCN [Fe(CN) 6 ] 3 + 6K + + 6H 2 [Fe(H 2 ) 6 ] K + + 6CN [Fe(CN) 6 ] 3 + 6K + + 6H 2 ALLW ECF for an equation showing formation of [Fe(CN) 6 ] 4 from [Fe(H 2 ) 6 ] 2+ : [Fe(H 2 ) 6 ] CN [Fe(CN) 6 ] 4 + 6H 2 Notice different charges on complex ions: LHS 2+, RHS 4 (ii) ligand substitution 1 ALLW ligand exchange R ligand replacement CARE: possible confusion with (c)(ii)

10 Question er Marks Guidance (e) F and G: 3 ALLW any attempt to show bidentate ligand 3 3 Bottom line is the diagram below. 3 3 Fe Fe Fe Fe 1 mark for each isomer Bonds must go to ligand atoms on EACH structure IGNRE charges on Fe 3+ and at this stage 3 charge outside brackets of BTH isomers AND N charges shown on Fe or within brackets Note: This mark is only available from structures with three bidentate ligands bonded to Fe via two s on each ligand IGNRE structure between two s in ligand even if slightly different Must contain 2 out wedges, 2 in wedges and 2 lines in plane of paper. For bond into paper, ALLW: (f) Fe Formula AND charge needed Total 12 ALLW other 2 ions containing: Fe AND AND Fe has ox no of +6 i.e. ALLW Fe 2 7 2, Fe , etc.

11 Question er Marks Guidance 4 (a) (1s 2 2s 2 2p 6 ) 3s 2 3p 6 3d 8 4s 2 (1s 2 2s 2 2p 6 ) 3s 2 3p 6 3d 8 2 ALLW 4s before 3d, i.e. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 IF candidate has used subscripts R caps, D NT ALLW when first seen but credit subsequently, i.e. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 8 4s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3D 8 For Ni 2+ ALLW 4s 0 in electron configuration (b) (i) Acts as a base R alkali AND removes/accepts a proton (from DMGH) 1 (ii) 4 1 (iii) (Each) DMG has 1 charge which cancel 2+ charge on Ni 2+ 1 ALLW 2 x = 0 For Ni 2+, ALLW Ni has an oxidation number of (+)2 ALLW Ni 2+ cancelled out by 2 DMG ALLW balanced for cancelled (iv) H 3 C C C CH 3 1 ALLW H for H ALLW CH 3 D NT ALLW H N N H H

12 Question er Marks Guidance (c) 7 max Marks are for correctly calculated values amount of Ni amount Ni(DMG) 2 R amount hydrated salt R amount Ni 2+ = = 8.9(0) x 10 3 mol ANNTATE WITH TICKS AND CRSSES, etc Note: The answers incorporate three different approaches to solving this problem. IF candidate attempts calculation via another method, consult your TL M values M(hydrated salt) = = (g mol 1 ) M(anhydrous salt) = = (g mol 1 ) H mass H 2 = = 1.12 g n(h 2 ) from mass or M values = = 6.2(2) x 10 2 R ~125.9 waters of crystallisation = = 7 R = Anion Molar mass of anion = ( x 18) = 96.1 (g mol 1 ) R Molar mass of anion = = 96.3 (g mol 1 ) Formula Formula of salt is NiS 4 7H 2 ECF answer above ALLW numerical answers (ALLW 281) IGNRE further figures ALLW numerical answers (ALLW 155) IGNRE further figures ASSUME that unlabelled 1.12 g applies to H 2 unless contradicted ALLW numerical answers (ALLW 126) ECF answer above 7 as whole number is required Note: Mark for 7 can be credited within formula BUT there must be some relevant working to derive ~7, e.g ALLW numerical answers (ALLW 96) Total 13

GCE Chemistry A. Mark Scheme for June Unit F325: Equilibria, Energetics and Elements. Advanced GCE PMT. Oxford Cambridge and RSA

GCE Chemistry A. Mark Scheme for June Unit F325: Equilibria, Energetics and Elements. Advanced GCE PMT. Oxford Cambridge and RSA Oxford Cambridge and RSA GCE Chemistry A Unit F325: Equilibria, Energetics and Elements Advanced GCE Mark Scheme for June 2015 Oxford Cambridge and RSA Examinations OCR (Oxford Cambridge and RSA) is a