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233/ 2
CHEMISTRY
Paper 2
(THEORY)
July/Aug. 2008
Time: 2 Hours
SIAYA DISTRICT SECONDARY SCHOOLS EVALUATION EXAMINATIONS - 2008
Kenya Certificate of Secondary Education (K.C.S.E)
233/ 2
CHEMISTRY
Paper 2
(THEORY)
July/Aug. 2008
Time: 2 Hours
INSTRUCTIONS TO CANDIDATES
 Write your name, index number and the name of your school in the spaces provided above.
 Answer ALL the questions in the spaces provided
 Mathematical tables and Electronic calculators may be used
 All working be shown where necessary.
FOR EXAMINER’S USE ONLY
Question
Maximum score Candidates score
1
12
2
12
3
12
4
09
5
13
6
13
7
09
Total Score
80
This paper consists of 12 printed pages.
Candidates should check the question paper to ensure that all pages are printed as indicated
and no question are missing
© The Siaya District Examination Panel
Chemistry 233/2
1
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1. a)
Element
Study the information given below and answer the questions that follow.
Atomic radius (nm)
Ionic radius
Formula of oxide
Melting point of oxide ( 0 C)
A
0.364
0.421
A2O
-119
B
0.830
0.711
BO2
837
E
0.592
0.485
E2O3
1466
G
0.381
0.446
G2O5
242
J
0.762
0.676
JO
1054
(i) Which elements are non-metals? Give a reason.
(2 marks)
(ii)
Explain why the melting point of the oxide of E is higher than that of the oxide of G (2
marks)
(iii) Give two elements that would react vigorously with each other. Explain your answer. (2 marks)
b) Study the information in the table below and answer the questions that follow (The letters do not
represent the actual symbols of the elements)
Ionisation Energy KJ/Mole
Element Electronic configuration
1st 1. E
2nd 1.E
X
2.2
900
1800
Y
2.8.2
736
1450
Z
2.8.8.2
590
1150
(i) What chemical family do the elements X, Y, Z belong?
(1 mark)
(ii)
What is meant by ionization energy?
(1 mark)
(iii) The 2nd ionization energy is higher that the 1st ionization energy of each. Explain(1 mark)
(iv) When a piece of element Z is placed in cold water, it sinks to the bottom and an effervescence of
a colourless gas that burns explosively is produced. Use a simple diagram to illustrate how this
gas can be collected during this experiment.
(3 marks)
2. Study the reaction scheme below starting with ethanol and answer the questions that follow.
CH3 C2 HOH
Step I
CH2 = CH2
Step II
Conc H2SO4
(1800C
Ni catalyst + H2
Step III
C
B
Step IV
Conc. H2 SO4 + Water
M
H
H
C
C
H
H
H2O
D
Step V
Ethanoic acid
n
E CH3 C-OOC2 HCH3
a) Write down the formula of compound B, C and D
b) Name the type of reaction represented by:
Step I:
Step II:
Step IV:
Step V:
c) (i) To what class of compounds does E and M belong?
E:
© The Siaya District Examination Panel
Chemistry 233/2
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(3 marks)
(1 mark)
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M:
(ii) Name the substance E.
(1 mark)
d) Write the equation of the complete combustion of ethanol
(1 mark)
e) If the relative molecular mass of M is 47,600; determine the value of n.
(C = 12.0 , H = 1.0)
(2 marks)
f) Using a chemical test, state how you can distinguish between CH2 = CH2 and
CH3CH3
(2 marks)
3. An experiment was carried out using magnesium ribbon and dilute hydrochloric acid of different concentrations. The
time needed to produce 50cm3 of the gas for every experiment was recorded in the table below:
Concentration
2.0
1.75
1.50
1.25
1.00
0.75
0.50
0.25
Of HCL (moles/litre)
Time in Seconds (s)
8.8
10.0
11.7
14.0
17.5
18.7
35.0
70.0
I
timesec 1 
a) Complete the table above for I
b) Plot a graph of rate i.e. I
timesec 1 
timesec 1 
(2 marks)
against concentration
(4 marks)
c) From your graph, determine the concentration needed to produce 50cm3 of hydrogen gas when
time is 15.0
seconds
(2 marks)
d) Neutralisation is a method of preparing salts.
(i) What is meant by neutralisation?
(1 mark)
(ii)Describe how you would prepare crystals of sodium nitrate starting with 200cm3 of 2M Sodium
hydroxide
solution.
(3 marks)
4. The table below shows the decay of phosphorous -32 with half life of 14.3 days.
Time (days)
Mass (g)
Radioactivity (counts per min)
0
200
400
14.3 (1st half life)
28.6 (2nd half life)
100
42.9 (3rd half life)
25
57.2 (4th half life)
a) (i) Complete the table above
(3 marks)
(ii) How long would it take for the mass of phosphorous to:
i)
¼ of its original mass
(1 mark)
ii)
1 of its original mass
16
(1 mark)
b) In an artificial process of nuclide may be made to disintegrate as shown below:
235
1
230
4
1
92 U +
0 X
90 Th
2
+
Y +
2 0X + Z
(i) X and Y are not the actual symbols of the particles involved. Use the properties given to identify the particles X and
Y.
X:
( ½ mark)
Y:
( ½ mark)
(ii) Identify Z
(1 mark)
c) Give two applications of radioactivity in industries
(2 marks)
5 a) The set up below was used during the electrolysis of 6M hydrochloric acid using inert electrodes.
Electrode B
Electrode A
6M hydrochloric
acid
(i) Identify the anions and cations present in the solution.
Anions:
Cations:
(ii)
Give a reason why a mixture of gases are obtained at electrode B.
© The Siaya District Examination Panel
Chemistry 233/2
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(1 mark)
(1 mark)
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Explain your answer
(3 marks)
(iii) During the electrolysis, a current of 2 amperes was passed through the solution for 3 hours, 20
minutes. Calculate the volume of the gas produced at electrode A (1 Faraday = 96500
Coulombs and molar gas volume at room temperature is 24000 cm3)
(3 marks)
b) Name two applications of electrolysis
(2 marks)
c) Use the information below on standard electrode potentials to answer the questions
that follow:
E  volts
Cu2+ + 2eCu
+ 0.34
2+
Fe + 2e
Fe
- 0.44
+
Na + e
Na
- 2.92
Mg2+ + 2eMg
- 2.71
2+
Pb + 2e
Pb
- 0.14
½ F2 + eF+ 2.87
½ Br2 + e
Br
+ 1.09
H+ + e½ H2
0.00
i) From the list select:
I. The strongest reducing agent. Give a reason
(1 mark)
II. The strongest oxidizing agent. Give a reason
(1 mark)
ii) Calculate the e.m.f. of the cell constructed in (i) above
(1 mark)
6. Study the scheme shown below and answer the questions that follow.
Ore Q
Step I
Excess N aoH (aq)
Resi due
Solution containing
Solution
containing
(Al(O
H) 4 )
(Al(OH)4
Spri nkl ing of
Sprinkling
of AL2O3 and CO2
Al
O 3 and CO
2
2
Solid R
St ep II
Solid Aluminiun Oxide
Cryolite
Cryolite
Na AlF
Na
3Alf6
Step III
Molten Mixture
3
Step IV
6
Mol ten Aluminiun
Step V
Uses of al uminium
Duralamin alloy for aircraft
parts and window frames.
Aluminium foil for lini ng
food packetts
a) (i) Name ore Q and solid R
Ore Q
(1 mark)
Solid R
(1 mark)
(ii) Explain why step I is necessary
(1 mark)
(iii) What happens in step II
(1 mark)
(iv) Why is cryolite added in step III.
(1 mark)
b) (i) Why is the anode replaced from time to time during the electrolysis?
(1 mark)
+
(ii) During the reaction in step IV Na and F ions are not discharged. Explain
(2 marks)
(iii) Write ionic equations for the reaction that takes place at the anode and cathode in step IV.
At anode
(1 mark)
At cathode
(1 mark)
© The Siaya District Examination Panel
Chemistry 233/2
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c) State two reasons why aluminium is preferred to copper in the manufacture of overhead electric
cables
(2 marks)
d) Aluminium is high in the reactivity series yet it does not react with water and air.
Explain.
(1 mark)
7. The flow diagram below represents how hydrogen sulphide can be used to prepare sulphuric acid.
Study it and answer the questions that follow.
AIR
Dry hydrogen
sulphide gas
Liquid T
BURNERS
SO3 (g)
Gas K
CHAMBER Q
TOWER
Solid x
OLEUM
a) Name:
(i)
Gas K:
( ½ mark)
(ii)
Liquid T:
( ½ mark)
……………………………………………………………………………………………………….
b) (i) What is the function of solid X in chamber Q?
(1 mark)
(ii) Write an equation for the reaction in chamber Q
(1 mark)
c) State and explain what would be observed if hydrogen sulphide gas is bubbled through:
(i) Aqueous copper (II) nitrate solution?
(2 marks)
d) Write an ionic equation for the confirmatory test for hydrogen sulphide gas.
(1 mark)
e) Write a chemical equation for the formation of concentrated Sulphuric (VI) acid
from the oleum.
(1 mark)
© The Siaya District Examination Panel
Chemistry 233/2
5
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