Page 400 - SUBSEC October 2017_Neat

02112020/CAPE/SPEC/MS/2017
- 7 –

CHEMISTRY
UNIT 01 — PAPER 02
MARK SCHEME
Question 3

S.O: Module 3: — 2.1, 3.4, 5.2, 5.6, 5.10
KC UK XS
(a) (i) variable oxidation number [1 mark]

(ii) form complex ions [1 mark]
3
(iii) act as catalysts [1 mark]

(b) (i) pink [1 mark] 2

(ii) pink [1 mark]

(c) Blue [1 mark] 1

(d) Ligands are groups that can donate electron pairs to metal 1
ions thus forming a co-ordinate bond. [1 mark]

(e) (i) blue precipitate [1 mark] 1

Cu(OH)2 [1 mark] 1

1
(ii) blue ppt dissolves forming deep blue solution [1 mark]

[Cu(NH3)4] 2+ [1 mark] 1

(f) Oxygen is transported to the tissues as a complex with the
haemoglobin that is found in the red blood cells. [1 mark]

CO can also form a complex with haemoglobin. [1 mark]

5
The stability constant for the haemoglobin – CO complex is
much higher than that of the haemoglobin – O2 complex, so CO
competes successfully with oxygen. [2 marks]

Therefore, the presence of CO can prevent oxygen from reaching
the tissues. [1 mark]

O2 + haemoglobin oxhaemoglobin

CO + haemoglobin carboxyhaemoglobin