Page 461 - SUBSEC October 2017_Neat

02212020/CAPE/SPEC/MS/2017
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CHEMISTRY
UNIT 2 — PAPER 02
MARK SCHEME
KC UK XS
(e) (i) Colourless gas evolves (1) which forms dense white fumes
with NH3 (1) [2 marks]
(ii) COOH/Carboxylic acid group present [1 mark]
5
(iii) Dil. HCl is added and the resulting solution heated
gently [1 mark]
(iv) The NH2 and amine group present [1 mark]

(f)  They show a steady gradation in physical properties
 Chemical properties are similar
3
 Relative molecular mass of consecutive members increase
by H or CH2 [1 mark each]




(g) (i) Cl – Cl  uv / sumlight 2 Cl [1 mark]


Cl + CH3CHCH3CH3  CH3 C CH3CH3 + HCl [1 mark]
 5
Cl + CH3CHCH3CH3  C H2CHCH3CH3 + HCl [1 mark]

 
CH3 C CH3CH3 + C l  CH3CClCH3CH3 [1 mark]

CH2CHCH3CH3 + C l  CH2ClCHCH3CH3 [1 mark]
(propagation steps also acceptable)

(ii) CH3CClCH3CH3
Stability of the tertiary free radical in the 2
intermediate stage [2 marks]

For 2 – methylpropene, the mechanism is electrophilic
(h)
addition (1). The double bond causes polarization of the

Chlorine molecule which produces the electrophile by
heterolytic fission (1). The mechanism for the 2-methyl
propane is free radical substitution (1) involving 4
homolytic fission. (1) [4 marks]

Total 30 marks 10 15 5