9701_w04_ms_2

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS

GCE Advanced Subsidiary and Advanced Level

MARK SCHEME for the November 2004 question paper

9701 CHEMISTRY

9701/02 Paper 2 (Structured Questions), maximum raw mark 60

This mark scheme is published as an aid to teachers and students, to indicate the requirements o f the examination. This shows the basis on which Examiners were initially instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. Any substantial changes to the mark scheme that arose from these discussions will be recorded in the published Report on the Examination.

All Examiners are instructed that alternative co rrect answers and unexpected appro aches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated.

Mark schemes must be read in conjunction with the question papers and the Report on the Examination. ?CIE will not enter into discussion or correspondence in connection with these mark schemes.

CIE is publishing the mark schemes for the November 2004 question papers for most IGCSE and GCE Advanced Level syllabuses.

Grade thresholds taken for Syllabus 9701 (Chemistry) in the November 2004 examination.

minimum mark required for grade:

maximum

mark

A B E

available

60 45 39 25

Component

2

The thresholds (minimum marks) for Grades C and D are normally set by dividing the mark range between the B and the E thresholds into three. For example, if the difference between the B and the E threshold is 24 marks, the C threshold is set 8 marks below the B threshold and the D threshold is set another 8 marks down. If dividing the interval by three results in a fraction of a mark, then the threshold is normally rounded down.

November 2004

GCE A AND AS LEVEL

MARK SCHEME

MAXIMUM MARK: 60

SYLLABUS/COMPONENT: 9701/02

CHEMISTRY

Paper 2 (Structured Questions)

1 (a) K c = 2

22[HI]]

][I [H (1) [1]

(b) K c =

2

(1.47)0.2740.274× = 0.035 (1) [1]

(c) At room temperature:

iodine is a solid/solids not K c expression (1)

[I 2(g)] is small/concn too small to be measured (1)

it takes longer to reach equilibrium/reaction is slower (1) [2 max]

(d) (i) ?H reacn = ?H for bonds broken – ?H for bonds made (1)

(ii) 2H – I → H – H + I – I

2 x 299 436 151 values (1)

?H = 2 x 299 – (436 + 151)

= + 11 kJ mol -1 (1) [3]

(e) (i) An acid that is completely ionised (1)

(ii) H I + H 2O → H 3O + + I -

(iii) I - (1) [3]

[Total 10]

2 (a) 4A l + 3O 2 → 2A l 2O

3 (1) [1]

(b) some answers may contain diagrams which are equivalent to the words given below

(i) A l 2O 3 has a giant structure of ions (A l 3+ and O 2-) (1)

held together by strong ionic bonds (1)

or a giant structure of atoms (1)

with strong covalent bonding throughout the lattice (1) (2 max)

(ii) SO 3 consists of small molecules

or is simple molecular

not simple covalent (1)

held together by weak van Waals’ forces (1)

(iii) SiO 2 is giant covalent/macromolecular (1)

with strong covalent bonds (1)

P 4O 10 is a simple molecular (as in SO 3) (1)

[7]

(c) (i) Na 2O + H 2O → NaOH

or MgO + H 2O → Mg(OH)2 (1)

(ii) P 4O 10 + 6H 2O → 4H 3PO 4

or P 4O 10 + 2H 2O → 4HPO 3

or SO 3 + H 2O → H 2SO 4 (1) [2]

[Total 10]

3 (a) (i)

[4]

(ii) anode 2C l -(aq) → C l 2(g) + 2e -

cathode 2H +(aq) + 2e - → H 2(g) (1)

or 2H 2O(l ) + 2e - → H 2(g) + 2OH -(aq) (1) [2]

(iii) anode C l goes from -1 to 0 (1)

cathode H goes from -1 to 0 (1) [2]

(i v ) sodium hydroxide (answer may be on diagram) (1)

[1]

(v) manufacture of

soap detergents

fluids

paper degreasing

rayon aluminium

glass dyes

bleach/NaC l O/Javel/Jik/Jenola any 2 [1]

(b) (i) H2 + C l2→2HC l (1)

(ii) HC l + H2O → H3O+ + C l- (1)

thus bonding goes form covalent to ionic [2]

(c) (i) AgNO3(aq) + HC l(aq) → AgC l(s) + HNO3(aq)

Ag+(aq) + C l-(aq) → AgC l(s) (1)

or

white ppt. forms (1)

(ii) ppt. dissolves to give colourless solution (1)

AgC l(s) + 2NH3(aq) → [Ag(NH3)2] C l(aq)

or Ag+(s) + 2NH3(aq) → [Ag(NH3)2]+(aq) (1)

either (i) or (ii) (1)

[5]

in

symbols

Correct

state

17]

[Total

4 (a) (i) C10H20O (1)

(ii) 156

allow e.c.f. on (a) (i) (1) [2]

(b) (i) primary (1)

alcohol (1)

(ii) alkene (1) [3]

(c) carbon atom number 6 circled (1) [1]

(d) (i) R CH2OH

C = C

CH3 H (1)

it does not have chiral C atom (1) [2] (ii)

(e) bromine is decolourised (1) [1]

(f) (i) R H (1)

C = C

CH3 CO2H

(ii) R H

C = C

CH3CH2OCOCH3 (1) (iii) R H

C

=

C

CH3 I I CH2Br

H Br

or R CH2Br

=

C

C

CH3 I I H

Br H

correct addition of HBr (1)

-CH2OH by Br (1) [4]

of

substitution

[Total 13]

5 (a) (i) H H

I I

CH3CHO + HCN → H–C–C–O–H (1)

I I

H C≡N

(ii) nucleophilic addition (1)

(iii) H H

δ+ δ-

I HCN I CH 3–C = O → CH 3–C –O - → CH 3–C–OH + CN - I I I

H –

CN CN CN

C = O dipole correctly shown (1)

attack on C δ+ by CN - (1) correct intermediate/correct curly arrow on C = O (1)

CN - regenerated (1)

[5 max]

(b) (i) H H

I I CH 3–C–OH + 2H 2O → CH 3–C–OH + NH 3 (1)

I I CN CO 2H (ii) hydrolysis (1)

[2]

(c) CH 3CHO → CH 3CH(OH)CO 2H

44 90 both M r values correct (1)

4.40 g → 9.00 g

% yield = 00

.9100

40.5×

expression (1)

= 60% value (1)

[3]

[Total 10]