MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY

Transcription

1 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY 9701/21 Paper 2 (AS Structured Questions), maximum raw mark 60 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 October/November 2015 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

2 Page 2 Mark Scheme Syllabus Paper 1 (a) regular arrangement / lattice of cations / positive ions surrounded by delocalised electrons (b) (i) electrical conductor corrosion resistant low density ductile owtte [max2] Giant / lattice (iii) (electrical) insulator (c) (i) Simple covalent / covalent molecule Weak intermolecular forces / VdW forces little energy needed to break down / overcome intermolecular / VdW forces Al Cl AlCl 3

3 Page 3 Mark Scheme Syllabus Paper (iii) pv = m M r RT mrt M = pv = = 267 r 3 6 pv = nrt n = pv RT = = M 1.36 = r = (iv) Al 2Cl 6 [13] 2 (a) (i) The enthalpy change when one mole of a compound is formed from its element(s) S(s) + 1½O 2 (g) SO 3 (l) (b) (i) (3 436) = = = 88 (kj mol 1 ) [3] Fe catalyst 200 atm ( )C [3] (iii) High T increases rate AND Low T improves yield owtte Chosen temp is a compromise High P favours / increases (both rate and) yield owtte pressure chosen limited by cost (of compression and thick walls ) [4]

4 Page 4 Mark Scheme Syllabus Paper (c) (i) 2NH 3 + H 3 PO 4 (NH 4 ) 2 HPO 4 (d) (i) NH 3 identified as base AND H 3 PO 4 identified as acid base accepts protons AND acid donates protons nitrates / fertilisers wash into rivers eutrophication / algal bloom / promote algal growth bacteria use up oxygen in decay process (oxides of nitrogen / NO x / NOs) cause acid rain [3] 2NO 2 + H 2 O HNO 2 + HNO 3 4NO 2 + 2H 2 O + O 2 4HNO 3 SO 2 + NO 2 SO 3 + NO AND SO 3 + H 2 O H 2 SO 4 3 (a) (i) structural isomers: (different molecules with) same molecular formula but different structural formulae chiral: has a carbon / C attached to 4 different groups / atoms / chains has no plane / line of symmetry / has non-superimposable mirror images CH 3 CH 2 CH(CH 3 )CH 2 CH 2 CH 3 3-methylhexane CH 3 CH(CH 3 )CH(CH 3 )CH 2 CH 3 / (CH 3 ) 2 CHCH(CH 3 )CH 2 CH 3 2,3-dimethylpentane [21] [4] (b) (i) C 7 H O 2 7CO 2 + 8H 2 O C 7 H O 2 7C + 8H 2 O

5 Page 5 Mark Scheme Syllabus Paper (iii) global dimming / PAN / smog / global warming (c) (i) (Free) Radical Substitution Cl 2 2Cl Cl 2 Cl + Cl C 7 H 16 + Cl C 7 H 15 + HCl C 7 H 15 + Cl 2 C 7 H 15 Cl + Cl C 7 H 15 + Cl C 7 H 15 Cl C 7 H 15 + C 7 H 15 C 14 H 30 Initiation; Propagation; Termination (used correctly) [5] [15] 4 (a) (i) CH 3 CH 2 OH + HCl CH 3 CH 2 Cl + H 2 O or CH 3 CH 2 OH + PCl 5 CH 3 CH 2 Cl + HCl + POCl 3 or CH 3 CH 2 OH + SOCl 2 CH 3 CH 2 Cl + HCl + SO 2 [1+1] NaOH / KOH warm / heat / reflux AND aqueous (b) (i) CH 2 =CH 2 / ethane / C 2 H 4 / CH 2 CH 2 White ppt / solid / suspension (iii) Ag + (aq) + Cl (aq) AgCl (s) (c) (i) CH 3 CHO / ethanal

6 Page 6 Mark Scheme Syllabus Paper CH 3 CH 2 OH higher bpt than CH 3 CHO ora due to hydrogen bonding in ethanol / stronger IMFs prevents further oxidation owtte [3] [11]