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Godfrey Carroll
5 years ago
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1 Atomic Structure Mark Scheme 4 Level International A Level Subject Chemistry Exam Board CIE Topic Atomic Structure Sub-Topic Paper Type Theory Booklet Mark Scheme 4 Time Allowed: Score: 83 minutes /69 Percentage: /00 Grade Boundaries: A* A B C D E U >85% 777.5% 70% 62.5% 57.5% 45% <45%

2 (a (i) 62 ( 8 Br 8 Br + ) 60 ( 8 Br 79 Br + ) 58 ( 79 Br 79 Br + ) ignore missing charges 8 ( 8 Br + ) 79 ( 79 Br + ) for molecular species [] for atomic species [] for 5 masses [] 58:60:62 =:2: [] 79:8 =: [] (b) either BrCH 2 CHBr-CHO or CH 2 =CH-CH 2 OH (double bond needed) [] reaction I: Br 2 (aq or in CCl 4 etc.), light negates solvent not needed reaction II: NaBH 4 or H 2 /Ni etc. (but not if A is CH 2 =CH-CH 2 OH) allow LiAlH 4 or Na/ethanol (reactions can be reversed) [] [] (c) C 3 H 6 OBr 2 = 26, 28 and 220 (any one) [] is is is is 87 is 89 is CH 2 OH + /CH 3 O + C 2 H 3 79 Br + C 2 H 3 8 Br + C 2 H 3 79 Br 2 + C 2 H 3 79 Br 8 Br + C 2 H 3 8 Br 2 + ignore missing charges 6 correct [4] 5 correct [3] etc if no mass numbers given [] only [4] [Total: 3 max 2]

3 2 (a (i) K a = [H + ][RCO 2 ]/[RCO 2 H] [] pk a = log 0 K a or logk a or log [H + ] 2 /[RCO 2 H] NOT ln; ; [ [2] (b) acid strength increases from no. to no. 3 or down the table or as Cls increase [] due to the electron-withdrawing effect/electronegativity of chlorine (atoms) [] stabilising the anion or weakening the O-H bond NOT H + more available [] chlorine atom is further away (from O-H) in no. 4, so has less influence [] (iii) either: ph = ½ (pk a log 0 [acid]) or K a = 0 pka =.259 x 0 3 = ½ ( ) [H + ] = (K a. c) = 3.55 x 0 4 [] = 3.4 (allow 3.5) ph = 3.4 ecf [] ([] for correct expression & values; [] for correct working) [6] (c) (i) catalyst [] (iii) CH 3 CH 2 CO 2 H + Cl 2 CH 2 CHClCO 2 H + HCl nucleophilic substitution NOT addition/elimination [] [] (iv) M r (CH 3 CH 2 CO 2 H) = 74 M r (CH 2 CH(NH 2 )CO 2 H) = g should give 0 x 89/74 = 2.03 g percentage yield = 00 x 9.5/2.03 = 79% [] ecf [] ([2] for correct answer) [5] (d) + NH 3 -CH(CH 3 )-CO 2 Allow charges on H of H 3 N, and COO but not C-O-O correct atoms [] correct charges [] [2] [Total: 5]

4 3 (a same proton no./atomic no./no. of protons () different mass no./nucleon no./no. of neutrons () [2] (b) number of isotope p neutrons electrons 56 Fe Co 27 () () () give one mark for each correct column allow () if no column is correct but one row is correct [3] (c) weighted mean/average mass of an atom (not element) compared with 2 C one atom of 2 C has a mass of exactly 2 [relative to / th 2 the mass of a 2 C atom would get 2] () () () or mass of mol of atoms () compared with 2 C () mol of 2 C has a mass of 2 g () A r = 54 x x x 2.7 () 00 = = 55.7 to 3 sf () 00 allow 55.9 if A r is calculated using instead of 00 [5] [Total: 0]

5 4 (a) Atoms which have the same number of protons (or same element) but different numbers of neutrons () [] (b) (i) 35 Cl () H 37 Cl () [2] (c) H Cl line at 36 has rel. abundance of These show 35 Cl and 37 Cl in ratio 3: () [or use of 35 and 37] [2] (d) Mean of the two isotopes 3 x 35 + x 37 = 35.5 () [] 4 [Total: 6]

6 Question point Marks 5 (a) oxygen: (s 2 ) 2s 2 2p 4 fluorine: (s 2 ) 2s 2 2p 5 (b) (i) F 2 O / OF 2 F O F (iii) bent or non-linear (c) (i) E o values: F 2 / F = 2.87 V and Cl 2 / Cl =.36 V fluorine (has the more positive E o so) is more oxidising redox (iii) Cl F + 2KBr KCl + KF + Br 2 [Total: 8]

7 Question Scheme Mark T 6 (a) The amount of energy required / energy change / enthalpy change when one electron is removed from each atom / (cat)ion in one mol of gaseous atoms / (cat)ions OR energy change when mole of electrons is removed from one mole of gaseous atoms / ions X(g) X + (g) + e gains 2 marks (b) (i) Group V / 5 / 5 3 Big difference between fifth and sixth ionisation energies s 2 2s 2 2p 3 ecf from (b)(i) if period 2 2 (c) (i) (Weighted) mean / average mass of an atom(s) (of an element) Relative to / 2 th of (the mass of an atom of) carbon-2 OR relative to carbon-2 which is (exactly) 2 (units) allow as an expression 2 Z Cl = : 2 A 35.5 r 68.87/35.5 So = 2 3.3/ A r A r = = = 32. to 3s.f Allow alternative correct methods 2

8 Question Scheme Mark T (d) (i) NaCl (+ aq ) Na + + Cl NaCl + H 2 O Na + + Cl + H 2 O SiCl 4 + 2H 2 O SiCl 4 + 4H 2 O SiCl 4 + 4H 2 O SiO 2 + 4HCl Si(OH) 4 + 4HCl SiO 2.2H 2 O + 4HCl Allow correct equation with other molar amounts of water NaCl is ionic AND giant / lattice NaCl dissolves / does not react SiCl 4 is covalent AND molecular / simple SiCl 4 is hydrolysed / reacts 2 4 (e) shape of SF 6 = Octahedral bond angle =

MARK SCHEME for the October/November 2007 question paper 9701 CHEMISTRY. 9701/04 Paper 4 (Theory 2), maximum raw mark 100

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2007 question paper 9701 CHEMISTRY 9701/04 Paper 4 (Theory 2),