SKEMA PSPM 2 2013_2014

SK026 : ANSWER 2013/2014

1 (a)(i) Enthalpy change in a chemical process is the same whether the process
takes place in one step or a series of steps.

(a)(ii)

2Al(s) + 3/2 O2(g) Al2O3(s) ∆H = −1669.8
5Al(s) + 9/2 H2(g) Al5H9(s) ∆H = −95.4
H2(g) + ½ O2(g) H2O(l)
∆H = −285.8

5Al(s) + 15/4 O2(g) 5/2 Al2O3(s) ∆H = −4174.5
Al5H9(s)
5Al(s) + 9/2 H2(g) ∆H = +95.4
9/2 H2(g) + 9/4O2(g)
9/2 H2O(l) ∆H = −1286.1

Al5H9(s) + 6 O2(g) 5/2 Al2O3(s) + 9/2 H2O(l)

∆H = − 4174.5 + 95.4 − 1286.1 = −5365.2 kJ

(b)

Electron flow e- V Cu(s)
Anode e-
Cathode
Salt bridge Salt bridge
KCl
Pb(s)

Pb2+(aq, 1.0 M) Cu2+ (aq, 1.0 M)

anode : Pb (s) Pb2+(aq) + 2e
cathode : Cu2+(aq) + 2e Cu(s)
overall : Pb(s) + Cu2+(aq) Pb2+(aq) + Cu(s)

Eo = Eo − Eo
cell cathode anode

= + 0.34 − (−0.13)

= + 0.47 V

1

E cell = Eo − 0.0592 log [Pb 2+ ]
cell [Cu 2+ ]
n

= 0.47 − 0.0592 log (1.0)
2 (0.1)

E cell = 0.44 V

2 (a) 2-methylpropane 2-methylpropene
CH3
CH3
CH3C Br CH3 C CH2
CH3
Br Br

CH3
CH3 C CH2

Br Br

(b) Br2, uv Br2, uv CH3
Br2, CH2Cl2
Br2, uv +CH3 CCH3 HBr

(c)
CH3

CH3 CHCH3

Br

CH3 Br2, CH2Cl2 CH3
CH3 C CH2 CH3 C CH2

Br Br

CH3 Br2, uv CH3
CH3 C CH2 CH3 C CH2

Br Br

(d) Br2, H2O / Br2, CH2Cl2 / KMnO4, OH-, cold

Observation :
2-methylpropene : Decolourised bromine water /

Decolourised Br2 in CH2Cl2 /
Decolourised KMnO4 and brown precipitate formed.

2-methylpropane : No observable changes with Br2, H2O / Br2, CH2Cl2 /
KMnO4, OH-, cold

2

CH3 Br2, H2O CH3
CH3 CHCH3 CH3 C CH2Br

OH

CH3 Br2, CH2Cl2 CH3
CH3 C CH2 CH3 C CH2

Br Br

CH3 - CH3
CH3 C CH2
KMnO4 , OH , cold +CH3 C CH2 MnO 2

OH OH

(e) CH3 CH3
CH3 C CH3 CH3 CHCH2OH
OH 2-methyl-1-propanol

2-methyl-2-propanol

Elimination / dehydration.

(a)(i) A : alcohol
3 B : phenol / aromatic alcohol

A : no reaction
(ii) O-Na+

B:

(iii) Phenol is more acidic than alcohol.

Phenoxide ion can delocalize its electrons.
Phenoxide ion is more stable than alkoxide ion.

(iv) OH OH

FeCl 3

FeCl 3

3

(b)(i) E : CH3 F: CH2

(b)(ii) Saytzeff’s rule.
More substituted alkene is more stable.

(b)(iii) D : C2H5ONa , C2H5OH, heat

(b)(iv) -base
-it remove proton from alkyl halide

4 (a)(i) i. O3
ii. (CH3)2S

(a)(ii) H

CC

CH3
O3 cleaves the C=C of alkene to give carbonyl compounds.

(a)(iii) Intermediates:

OMgBr OMgBr
C CH3 CH
CH(CH 3)2 CH(CH 3)2

Products:

OH OH
C CH3 CH
CH(CH 3)2 CH(CH 3)2

4

(a)(iv) H has a methyl ketone group, CH3 C

O O
O
C O-
C CH3 I2 / NaOH CHI 3
+

(b) COOH CH 2OH CONHCH 2CH 3
COOH CH3 CH3

(K) (L) (M)

COCl COOCH(CH 3)2
CH3 CH3

(N) (P)

5 Order of reaction is an exponent in a rate law with respect to the corresponding
reactant.

The minimum kinetic energy that must be processed by the reactants in order to
result in an effective collision.

Rate = k [NO2]

1 / T (K-1) ln k (s-1)
2.1 x 10-3 −8.6
1.9 x 10-3 −5.9
1.7 x 10-3 −3.5
1.5 x 10-3 −1.3

ln k

1/T (x 10-3 K-1)

5

ln k = − Ea  1  + ln A
R T

slope = − Ea
R

−12.167 K = − Ea
R

Ea = 12.167 x 8.314 J mol-1
Ea = 1.01 x 102 kJ mol-1

6 Reagents: R : H2O, H+
T : KMnO4, H+, ∆

Q : CH3 CH CHCH CH2 CH3 4-methyl-2-hexene
CH3 3-methyl-3-hexanol

S : CH3
CH3 CH2 CH2 C CH2 CH3
OH

U : CH3COOH ethanoic acid

V : CH3CH2 CHCOOH 2-methylbutanoic acid
CH3

Q : −alkene
−contain chiral centre
−has two same substituents attached to C=C
−can exist as cis-trans isomers

S : 3o alcohol

U and V are carboxylic acids

CH CHCH3 CH CHCH3

C C
H CH2CH3 H

CH3 CH3CH2 CH3

6

HH H3C H
C C
CC
H CH CH2CH3
H3C CH CH2CH3

CH3 CH3
cis isomer trans isomer

Mechanism:

CH3 CH +C CH2 CH3 H O+ H CH3 CH2 C+ CH CH2CH3
H H CH3
CH3

CH3 1,2 - H shift CH3 CH2 CH2 C+ CH2CH3
CH3 CH2 C+ C CH2CH3 CH3

HH H
H O+
+CH3 CH2 CH2 C+ CH2CH3 H OH CH3 CH2 CH2 C CH2CH3

CH3 CH3

H

H O+ OH

+CH3 CH2 CH2 C CH2CH3 HO H +CH3 CH2 CH2 C CH2CH3 H O+ H

CH3 CH3 H

7 (a) Benzene is aromatic because
✓ It is cyclic with conjugated C=C bonds
✓ Pi electrons are delocalized within the ring
✓ Planar

Kekule structures of benzene:

7

Preparation of W: CH(CH 3)2

(CH 3)2CHCl Br2, uv
AlCl 3 C(CH 3)2
Br
C(CH 3)2 CN -
CN

X : CH3CH2CH2CH2Br
1o alkyl halide / reaction occurs at C1

Mechanism: CH 2CH 2CH 3 slow CH 2CH 2CH 3
CH 3O-
H C Br CH3O .... C.... Br
H
HH

transition state

CH 3O CH 2CH 2CH 3
Bimolecular nucleophilic substitution or SN2
CH
H

The reaction rate decreases because CH3OH is a weak nucleophile.
[alkyl halide] or [Nu]

8 a) 1o CH3 CH2CH2 CH2

NH2

2o CH3 CH2CH2 NH or CH3CH2 NH or CH3 NH

CH3 CH2CH3 CH3CH CH3

3o CH3 NCH2CH3
CH3

8

Inductive effect:
✓ 2o amine more basic than 1o amine
✓ More alkyl group (EDG) attached to the N of the 2o alkyl amine.
✓ The electron density is greater around N atom and can donate a lone

pair electron / accept proton easily in the 2o amine.

Resonance effect:

✓ Aniline less basic than the 1o , 2o and 3o aliphatic amine.
✓ Aniline is strongly stabilized by resonance.
✓ Lone pair electron on N is delocalized in the benzene ring.

CH3 CH2CH2 CN i. LiAlH 4 CH3 CH2CH2 CH 2NH 2
ii. H 3O+

or NaBH 4 in methanol
or H2 / catalyst

(b) O O
HO OH H2N

OH
CH3

O
HO NH

OH
O CH3

peptide bond

(c) Monomer : H2C=CHCl

HH n
CC
H Cl

Addition polymerisation

Free radical

R CH2 CHCl

9