Mark Scheme for Mock Paper 2

Mark Scheme for Mock Prelim Paper 2 Mark Scheme Abbreviations ; separate marking points (1 marking point is 0.5 marks, unless stated otherwise) R reject I ignore COND mark awarded is conditional on previous marking point OWTTE or words to that effect (accept other ways of expressing the same idea) underline actual word given must be used by candidate (grammatical variants accepted) ( ) the word / phrase in brackets is not required ORA or reverse argument

Question Answer Guidance 1 a i giant metallic structure / lattice; sea of delocalised electrons AND Cs+ cations (arranged in a lattice); electrostatic attraction / electrostatic forces of attraction (known as metallic bonding); between electrons and Cs+ cations; R metallic bonding Candidates are expected to explain the origin of metallic bonding, because the word ‘metallic’ does not give any insight into the bonding present. ii Li has stronger metallic bonding than Cs; because charge density of Li+ cation is higher than that of Cs+ cation; • Li is harder to vapourise than Cs Pb has more valence electrons than Cs; because Pb is in Group 14, while Cs is in Group 1; • Pb has more active electrons than Cs Answers missing either one of the bullet points will be deducted 0.5m. The total number of marks awarded must be non-negative. b i E⦵(Li+/Li) = -3.04 V AND E⦵(Na+/Na) = -2.71 V AND E⦵(K+/K) = -2.92 V;

inconsistent reducing power down the group OR reducing power is approximately invariant / constant OR reducing power remains strong; OWTTE ii number of principal quantum shells increases down the group; valence electron is further AND less attracted to the nucleus; OWTTE 1st ionisation energy decreases down the group (The conclusion must be present. Deduct 0.5m for no conclusion. No marks awarded for this question for wrong conclusion.) The total number of marks awarded must be non-negative. c i Cs + H2O → Cs+ + 0.5 H2 + OH- reaction has Ecell > 0; OWTTE because Group 1 metals have E⦵(X+/X) around -3 V / more negative than -2 V which is more negative than E⦵(H2O/H2) = -0.83 V; OWTTE Cs metal will react with water (spontaneously) to form Cs+ ions; unable to maintain [Cs+] = 1 mol dm-3 OR cannot place Cs in water; The reduction potential of Cs+/Cs is not given in the Data Booklet, so it is the job of the candidate to offer further insight of what they would expect this value to be. ii M1 for amount of electrons ne-=ItF=2.00×48×60×6096500=3.5813 mol A1 for correct answer mass = 3.5813 × 132.9 = 476 g

d Award 1 mark for 3 points. Award 2 marks for 5 points. • down Group 1, the charge density of the cation decreases (because ionic radius increases down the group) • polarising power of the cation weakens / decreases down the group • electron cloud of peroxide ion is less distorted / polarised down the group • more energy required to break the O—O bond in the peroxide ion down the group • decomposition temperature increases down the group 2