Page 481 - SUBSEC October 2017_Neat

02212032/CAPE/SPEC/MS/2017
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CHEMISTRY
UNIT 2 — PAPER 032
MARK SCHEME
KC UK XS
Question 2

S.O.: Module: 2 ----2.4, 2.5

(i) Pale yellow  pink tinge [1 mark] 1

(ii)

Burette readings KMnO 4 /H +

Reading/cm 3 1 2 3

Final 11.50 17.20 31.50

Initial 0.50 6.70 20.90
4

Difference 11.00 10.50 10.60

Correct burette readings = [4 marks]

(If one incorrect = 3 marks)
(If two incorrect = 2 marks)

(If THREE incorrect = 1 mark)

(More than THREE incorrect = 0 marks)

Volumes recorded to 2 decimal places

10 5 .  10 6 .
(iii) = 10.55 cm 3 [1 mark]
2 1

-3
-
(iv) Conc. of MnO4 (aq) = 0.02 mol dm
-3
-
No. of moles of MnO4 = (10.55 x 0.02 x 10 )

2+
-3
No. of moles of Fe (aq) = (5 x 10.55 x 0.02 x 10 )

[1 mark]

2+
3
No. of moles of Fe (aq) in 1 dm

5 x 10 . 55 x . 0 02 x 10  3
=
20 3
-2
= 5.275 x 10 mol dm -3 [1 mark]

2+
-3
Conc. of Fe = (5.275 x 10 -2 x 56) = 2.95g dm [1 mark]