1.
a) Hydrogen peroxide, H2O2, reacts with potassium iodide, KI, in the presence of
hydrochloric acid, HCl, according to the following equation:
H2O2(aq) + 2I-(aq) + 2H+(aq) 2H2O(l) + I2(g)
The rate equation for the reaction is rate = k [H2O2] [I-].
i) State the order of reaction with respect to KI and HCl.
ii) TABLE 1 shows the experimental results obtained for the above reaction.
Predict the values of A and B.
iii) What can be done to increase the value of the rate constant?
[5 marks]
TABLE 1
Initial concentration (mol dm-3)
-3 -1
Initial rate (mol dm s )
[H2O2] [H+] [I-]
1.0 x 10-4 0.1 0.1 0.1
2.0 x 10-4 A 0.2 0.1
B 0.2 0.1 0.2
b) The rate constant for the reaction below is 0.0234 s-1 at 400oC and 0.750 s-1 at 500oC.
Calculate the activation energy, Ea, in kJ mol-1 for this reaction.
N2O(g) + NO(g) N2(g) + NO2(g) ∆H = −110 kJ mol-1
Draw a labelled energy profile diagram for the reaction and calculate Ea for the
reversed reaction. [5 marks]
2. a) The enthalpy of combustion of benzoic acid is -3226.7 kJmol-1. When 3.2 g benzoic
acid, C6H5COOH is completely combusted in a bomb calorimeter containing 2.0 kg
of water, the temperature of the water increased by 3.8⁰C. Calculate the heat capacity
of the calorimeter. [5 marks]
b) Calculate the enthalpy of hydration of Cl- in the dissolution process of LiCl in water
using energy cycle method. Given:
Lattice energy of LiCl = −846 kJ mol-1
Enthalpy of solution of LiCl in water = −37 kJ mol-1
Enthalpy of hydration of Li+ = −510 kJ mol-1 [5 marks]
3. a) A galvanic cell undergo the following reaction:
Mg(s) + Cd2+(aq) Mg2+(aq) + Cd(s)
The magnesium electrode was immersed into a 1.00 M solution of MgSO4 and the
cadmium electrode was immersed into a solution of unknown Cd2+ concentration. The
potential of the cell was measured to be 1.54 V at 298 K.
i) Calculate E°cell
ii) Calculate the concentration of Cd2+ in the cell.
iii) Predict what happens to voltage when the Mg2+/Mg half cell is replaced with
Zn2+/Zn half cell (1.00 M Zn2+).
[E°Cd2+/Cd = -0.40 V ; E°Zn2+/Zn = -0.76 V ; E°Mg2+/Mg = -2.37 V ]
[3 marks]
b) A galvanic cell consists of magnesium electrode immersed in 1.0 M magnesium
nitrate solution and a silver electrode immersed in 1.0 M silver nitrate solution and a
salt-bridge.
[E° Mg2+/Mg = -2.36 V , E° Ag+/Ag = +0.80 V]
i) Write the cell notation for the above reaction.
ii) State the oxidizing agent. [2 marks]
4. Compound C is an unsaturated cyclic compound which reacts with HBr in the
presence of H2O2 to produce D while catalytic hydrogenation of C produces E. E
reacts with Br2 in the presence of sunlight to produce F, the major product. Upon
treatment with hot acidified KMnO4, C yields G.
H3C OH
O O
G
i) Draw the structure of C, D and E
ii) Write the reaction mechanism to show the formation of the most stable
reaction intermediate during monobromination of E to produce F.
[5 marks]
5. Compound H is formed when benzene reacts with 2-bromopropane in the presence of
AlBr3. Bromination of H in light gives I, the major product and chlorination of H in
the presence of FeCl3 yields J and K. When H is treated with acidified solution of
KMnO4, compound L is formed. Hydrolysis of I gives M, while nitration of L forms
N. Draw the structures of H, I, J, K, L, M and N. [7 marks]
6. a) TABLE 2 shows the relative rates of SN2 reactions for alkyl halides.
TABLE 2
Class of Alkyl halide Compound Relative rate
Methyl bromomethane 30
1o bromoethane 1
2o P 0.03
3o 2-bromo-2-methylpentane 0.001
i) Explain the relationship between the class of alkyl halide with the
relative rates of reaction.
ii) Give one example of compound P (a four carbon alkyl halide)
b) Arrange the following alkyl bromides in order of decreasing reactivity towards SN1
reaction. Explain your answer.
2-bromopropane, 1-bromopropane, 2-bromo-2-methylpropane
Propose the mechanism for the methanolysis of the most reactive alkyl bromide
above. [7 marks]
OH
7. CH3
Compound J
Compound Q
a) Suggest a carbonyl compound and Grignard reagent to produce Q.
b) Q can also be prepared from hydrolysis of haloalkane. Propose a suitable
haloalkane and write the chemical equation for this reaction.
c) 2-propanol reacts with iodine in aqueous solution of NaOH to produce light
yellow precipitate but compound Q does not. Explain the observation.
[5 marks]
U
U
8. N
CH3CH2CH2OH
NaCN
R CH3 I2, NaOH
P
V + Q
HCl
M
I
i. S
ii. T
CH(OH)CH 3
UII
a) Draw the structures of U and V
b) Give the reagents S and T
c) Suggest a chemical test to differentiate compound I from II. State the observation
and write the reaction equation.
[7 marks]
9. a) Reaction of an unsaturated carboxylic acid with hydrochloric acid yields compound
Y and Z as shown below:
HCl
CH3 CH CHCOOH +
KY + L
Z
J
X
Draw the structures of Y and Z. Predict the more acidic product and explain.
b) Methanoic acid is the only carboxylic acid that reacts with Tollens’ reagent. Explain.
c) Terylene has the repeating unit as shown below. Give the structural formula of the
monomers and name the type of polymerization for the formation of terylene. Give
one usage of terylene.
O O
C C OCH2CH2O
n
[9 marks]
