Page 401 - SUBSEC October 2017_Neat

02112020/CAPE/SPEC/MS/2017
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CHEMISTRY
UNIT 01 — PAPER 02
MARK SCHEME

KC UK XS
(g) Mg = +2

2-
[A1 OH4] - SiF6 PO 3- 3
X – 4 = -1 x – 6 = -2 x – 6 = -3
X = +3 x = +4 x = +3
A1 = +3 Si = +4 P = +3

[4 correct = 4 marks]
[3 correct = 3 marks] 5
[2 correct = 2 marks]
[1 correct = 1 mark]

Oxidation number results from the need of elements to
6
Achieve configuration of ns np
2

Hence, oxidation numbers: +2, +3, +4, +3 [1 mark]

(h) (i) Atomic radius: half the distance between two
covalently bonded atoms. [1 mark]

OR 1

Distance of nearest approach to another identical
atom. [1 mark]

Ionic radius: this is assigned by considering the
distance between the two centres of adjacent ions in 1
a crystal lattice. [1 mark]

1
(ii) As Group II is descended, atomic size increases due
to electrons in additional valence shell. [1 mark]

As Group II is descended, ionic size increases: ion
2
6
has E.C. given by (n-1)s (n-1)p . [1 mark] 1

(i) Oxides vary: CO, SiO are neutral; SiO are neutral;
GeO, SnO, PbO are amphoteric. [1 mark]

CO, SiO – no reaction with acids or bases [1 mark]

2+
GeO, SnO, PbO – with acids give divalent ions (M )
[1 mark] 5

GeO, SnO, PbO – with alkalis produce complex ions
2-
[M(OH)4] [2 marks]

Total 30 marks 10 15 5