Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level. Published

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1 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/2 Paper 2 AS Level Structured Questions May/June 207 MARK SCHEME Maximum Mark: 60 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 7 printed pages. UCLES 207 [Turn over

2 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 (a) The mass of a molecule OR the (weighted) average / (weighted) mean mass of the molecules Relative / compared to (the mass) of an atom of carbon 2 2 OR on a scale in which a carbon 2 atom / isotope has a mass of (exactly) 2 (units) (b)(i) 3 (b)(ii) 8 (b)(iii) C 3 H 8 O + 4½O 2 3CO 2 + 4H 2 O (b)(iv) AND propan 2 ol / 2 propanol AND propan ol / propanol Alternative answers (any two): AND butan ol / butanol AND butan 2 ol / 2 butanol AND (2 )methylpropan ol / (2 )methyl propanol AND (2 )methylpropan 2 ol / (2 )methyl 2 propanol UCLES 207 Page 2 of 7

3 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 (b)(v) correct conversions of data to SI/consistent units p = ; V = ; T = 393 calculation of n ( = pvirt) from M values n = calculation of mass m ( = n Mr) AND answer correct to 3sf m = = (g) Alternative answer for using C 4 H 0 O: m = = (g) Total: 0 2(a) substance type of bonding type of lattice structure copper metallic giant/metallic ice covalent OR hydrogen(-bonding) / H( bonding) hydrogen-bonded / simple / molecular silicon(iv) oxide covalent giant (molecular) / macromolecular iodine covalent simple / molecular sodium chloride ionic giant / ionic 2(b)(i) hydrogen bonding UCLES 207 Page 3 of 7

4 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 2(b)(ii) H-bond between O and H of different molecules minimum three partial charges (in a row) over two H 2 O molecules, i.e.: either δ O H δ δ O or H δ δ O H δ+ lone pair of electrons on O of H-bond, in line with H-bond 2(c)(i) X = liquid AND Z = solid Y = liquid and solid OR liquid / solid OR liquid OR solid 2(c)(ii) (kinetic) energy reducing motion slowing owtte 2(c)(iii) energy given out / released forming bonds / forming bonds exothermic compensates for / counteracts heat loss / cooling owtte Total: 5 UCLES 207 Page 4 of 7

5 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 3(a)(i) A 3(a)(ii) H 3(a)(iii) G 3(a)(iv) B 3(a)(v) F 3(b)(i) (strong) heating (to provide / overcome) high activation energy 3(b)(ii) white flame / white light / white smoke / white solid 3(b)(iii) Mg(s) + 2H2O(l) Mg(OH) 2(s) + H 2(g) 2 3(c)(i) 2Mg(NO 3 ) 2 2MgO + 4NO 2 + O 2 3(c)(ii) CaCO 3 CaO + CO 2 CaO + H2O Ca(OH) 2 3(d)(i) reduce acidity in soil / increase ph of soil (both) basic / base(s) 3(d)(ii) + 2+ CaCO 3 + 2H Ca + CO 2 + H2O OR + 2+ CaCO + 2H Ca +H CO Total: 6 UCLES 207 Page 5 of 7

6 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 Question 4(a)(i) Answerr (molecules / isomers with) the same molecular formula / same number of atoms of each element different structural / displayed formulae / arrangement of bonds Marks 4(a)(ii) sp 2 overlap of (2)s with two (2)p (atomic) orbitals sp 3 overlap of (2)s with all three (2)p (atomic) orbitals 4(a)(iii) 4(b)(i) sp 2 = 6 24 sp 3 = (b)(ii) 4(b)(iii) (electrophilic) addition bromine decolourises / turns colourless / fades (from orange / brown) HOCH 2 CHBrCH 2 Br OR 4(b)(iv) 4(c)(i) CO 2 / carbon dioxide P = propanal Q = propanone UCLES 207 Page 6 of 7

7 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 Question 4(c)(ii) Answerr Marks tr(i)iodomethane / CHI 3 / / 4(d)(i) 4(d)(ii) (molecules / isomers with) the same (molecular and) structural formula Any two of: chiral centre / C attached to four different groups / atoms a non-super(im)posable mirror images different spatial / 3D arrangement of atoms (owtte) different rotation of plane-polarised light curly arrow from lone pair on :C N to C (δ+) correct dipole on carbonyl δ+ C=O δ AND curly arrow from bond b to O (δ ) correct intermediate, including C O AND curly arrow from lone pair to H + Total: 9 UCLES 207 Page 7 of 7