Chemistry STPM Sem 3 MSAB Pre-Trial Answer

MAKTAB SULTAN ABU BAKAR UJIAN PENILAIAN PRA-PENTAKSIRAN SEM 3 2014 SUBJECT : CHEMISTRY Section A [15 marks] 1

A

6

D

11

C

2

D

7

A

12

D

3

C

8

D

13

D

4

B

9

C

14

C

5

C

10

B

15

A

16. a) Each correct structure = 1 x 4

18 .b) Each structure = 1 m x 8 B : Cl2 ; uv A : CH3CH2Cl / AlCl3

i. C: ii.

E: G : CH3Cl / AlCl3

iii. iv. b) Geometrical isomer present @ each C in C=C is surrounded by 2 different atoms / group of atoms

cis - isomer (Structures [1] 17. I ii. iii. iv.

[1]

F : CH3COCl / AlCl3

H:

19. a) m1 : Mechanism : SN2 m2 : Nucleophile : CN-. m3 : Structure : CH3CH2CH2CH2Cl m4 : and CH(CH3)2CH2Cl m5 - m8 refer to diagram below

[1] [1] [1] [1] [4]

trans - isomer label cis trans [1] )

correct type of reaction [1] x 4 reagent [1] x 4 Type of reaction Reagent Free radical substitution Br2 under UV / hv Alumina @ conc. H2SO4 Elimination under heating Cold, dilute KMnO4/H+ Oxidation @ OHEthanolic conc. NH3 Nucleophilic substitution under reflux

18. a) i. Calculate mole [1] ; stating empirical formula [1] Element Carbon, C Hydrogen, H Mass 92.3 7.7 Mole 92.3/12 = 7.7 7.7 / 1 = 7.7 Mol ratio 7.7 / 7.7 = 1 7.7 / 7.7 = 1 Empirical formula = CH ii. (CH)n = 104 ; (13) x n = 104 ; n = 8 Molecular formula = C8H8 [1] Structure [1] iii. Major [1]

D : I2 in NaOH

Minor [1]

iv. to produce polystyrene / container.

(no label only 1)

b) i. rate = k[CH3CH2CH2CH2Cl][CN-] / CN- is first order [1] - increasing CN- will increase the rate of reaction [1] ii. - rate of reaction increased [1] Since C-Br bond length is longer / bond strength weaker [1]

c) m1 : 2-chloro-2-methylpropane [1] m2 : m3 : steric hindrance 20.a) m1 : Acidity decrease according to order

[1] [1] [1]

m2 : cyclohexane is electron-donating / positive inductive [1] m3 : caused alkoxide more readily to accept proton @ cause equilibrium shift to left [1] m4 : benzene is electron withdrawring / negative inductive [1] m5 : caused phenol more readily to donate proton @ caused equilibrium shift to right [1] m6 : NO2 gives negative inductive / electron withdrawing / stabilised phenoxide ion formed [1]

20. b) Alternative 1 : Reagent : acidified KMnO4 / H+ [1] Observation : purple colour decolourised by cyclohexanol but not by phenol [1] Equation :

20 c) m1 : Saytzeff rule : in elimination of H-X or H2O, H is preferable to eliminate from neighbouring C with less H [1] [1] m2 : reagent : alumina / conc. H2O under heating m3 : Structure of 2,3-dimethylpentan-3-ol [1]

[1]

Alternative 2 : Reagent : bromine water [1] Observation : brown colour decolourised and white precipitate is formed when added to phenol [1] Equation : bromination of phenol [1]

m4 ; m5 ; m6 - 3 products of dehydration

[3]