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5070 s14 ms 31 .pdf



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CAMBRIDGE INTERNATIONAL EXAMINATIONS
GCE Ordinary Level

MARK SCHEME for the May/June 2014 series

5070 CHEMISTRY
5070/31

Paper 3 (Practical Test), maximum raw mark 40

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 2014 series for most IGCSE, GCE
Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2
1

Mark Scheme
GCE O LEVEL – May/June 2014

Syllabus
5070

Paper
31

(a) Temperature readings
F: full set of temperatures provided for columns D and E (1)
R: temperatures recorded to 0.5 °C (1)
S: temperature rises correctly calculated, 6 correct (1) OR all correct (2)
P: pattern of results:
a general rise then fall (1)
experiments 1–3 increasing temperature rise (1)
experiments 4–7 decreasing temperature rise (1)
Accuracy:
For each of the experiments 1–7 give 1 mark for each temperature rise within 1.0 °C
of the supervisor’s value (7)

[14]

(b) Graph
Correct plotting of all the points (1)
Two intersecting straight lines which fit the results as plotted (1)

[2]

(c) Volume of P
Correct recording of the volume from the graph at the point of intersection of the two
lines (1)

[1]

Mark parts (d) – (f) using the candidate’s volume of P.
Assuming the volume of P is 23.0 cm3:
(d) Number of moles of HCl in 23.0 cm3 of P
=

23.0×1.50
1000

= 0.0345 (1)

[1]

(e) Number of moles of NaOH which react
= 0.0345 (1)

[1]

(f) Concentration in mol / dm3 of Q
Volume of Q
50.0 – 23.0 = 27.0 (1)
Concentration of Q
=

0.0345×1000
27.0

= 1.28 (1)

[2]
[Total: 21]
© Cambridge International Examinations 2014

Page 3
2

Mark Scheme
GCE O LEVEL – May/June 2014

R is hydrochloric acid

Syllabus
5070

Paper
31

S is sodium thiosulfate

Test

Notes

General points
For ppt
allow solid, suspension, powder
For gases
Name of gas requires test to be at least partially correct.
Effervesces = Bubbles = gas vigorously evolved but not gas evolved
Test 1
bubbles

(1)

gas pops with a lighted splint

(1)

hydrogen

(1)

metal disappears

(1)

to score hydrogen mark there must be some
indication of a test e.g. ‘popped with a splint’,
‘tested with a burning splint’
[4]

Test 2
(a) white ppt

(1)

(b) ppt remains

(1)

[2]

Test 3
white or yellow ppt

(1)

manganate(VII) decolourised

(1)

pungent gas / sulfur dioxide

(1)

[3]

(1)

[1]

allow turns colourless / white / brown

Test 4
decolourised

allow turns colourless

Test 5
white / yellow / red / brown ppt

(1)

colour of ppt darkens

(1)

[2]

© Cambridge International Examinations 2014

Page 4

Mark Scheme
GCE O LEVEL – May/June 2014

Test

Syllabus
5070

Paper
31

Notes

Test 6
(a) solution turns purple / red / violet(1)

accept dark brown

solution finally colourless / pale
yellow
(1)
(b) green

accept colour fades / becomes paler
accept black-green

(1)

ppt

(1)

insoluble in excess

(1)

[5]
[maximum 16 marks from 17 scoring points]

Conclusions
Cation in R is H+. (In Test 1 metal reacts.) (1)
Anion in R is Cl–. (In Test 2 there must be a white ppt which remains in nitric acid.) (1)
If both ions in R are correct but inverted, allow one mark from the previous two.
S is a reducing agent. (Test 4 decolourised or green ppt in Test 6) (1)

[3]
[Total: 19]

© Cambridge International Examinations 2014


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