P530/2
CHEMISTRY
PAPER TWO
OCT/NOV, 2019
2HR/30MIN
BUSOGA COLLEGE MWIRI
UGANDA ADVANCED CERTIFICATE OF EDUCATION
MID TERM III EXAMINATION
CHEMISTRY
PAPER TWO
DURATION: 2HOUR 30 MINUTES
INSTRUCTION TO THE CANDIDATES:
Answer three questions from SECTION A and any two from SECTION B
Any additional questions will NOT be marked
Illustrate your answers with equations where applicable.
Start every question from a fresh page
Mathematical tables and graph papers are provided.
Non-programmable scientific electronic calculators may be used.
1 mole of gas occupies 22,400 cm3 at s.t.p
1 mole of gas occupies 24,000 cm3 at r.t.p
Molar gas constant R=8.314JK-1 mol-1
©DEPT. OF CHEMISTRY, BUSOGA COLLEGE MWIRI
2019
SECTION A
1. An organic compound T on complete combustion yielded 13.2 g of
carbon dioxide and 2.7 g of water. When 4.7 g of T was vapourised at
273 ° C and at 760mmHg, it occupied a volume of 2.7x 10-3 m3.
a) i). Calculate empirical formula of compound T (02 marks)
ii) Determine the molecular formula of compound T (021/2
marks)
b) Compound T burns with a sooty flame, identify T (01/2 marks)
c) i) Describe at least three evidences put to explain the structure of
compound T (06 marks)
ii). Show how compound T can be synthesized from carbon and
calcium oxide. (03 marks).
2. a). what is meant by the terms
i. order of reaction (01 mark)
ii. Half-life of a reaction (01 mark)
iii. Rate equation (01 mark)
b). The rate equation for the reaction
S2O3 2- (aq) + 2 H + (aq) SO2 ( aq) + S (S) + H2O (l)
is Rate= K [ S2O32-][H+]2
i. State how the rate of reaction will be affected if the concentrations
of the reactants are both doubled (021/2 marks)
c). The table below shows the kinetic data for the reaction between hot
aqueous potassium hydroxide and alkyl bromide (C4H9Br).
C4H9Br (l) + KOH (aq) C4H9OH (aq) +KBr (aq)
Experiment [C4H9Br] /moldm- [KOH] / moldm-3 Initial Rate
3
moldm-3 s-1
1 1.0 X 10-3 1.0X10-3 5.0X10-8
2 2.0 X 10 -3 1.0 X 10 -3 1.0X10-7
3 2.0 X10 -3 2.0 X 10 -3 2.0X 10-7
i. Determine the overall Order of reaction (02 marks)
©DEPT. OF CHEMISTRY, BUSOGA COLLEGE MWIRI
2019
ii. Determine the rate constant for the reaction and state its units (03
marks)
iii. Identify the alkyl bromide (01 marks)
d) Write the mechanism for the reaction in (c) above (04 marks)
e) Draw a well labelled energy level diagram for the reaction
mechanism illustrated in (d) above ( 03 marks).
3. Carbon, silicon, germanium tin and Lead are elements of Group (IV) of the
Periodic Table.
a) Write the electronic configuration of the outer most energy level of
Group (IV) elements (01 mark)
b) Describe how;
i. Carbon, silicon, germanium and Lead react with water ( 07 marks)
ii. Oxides of the element of carbon, silicon and Lead react with
sodium hydroxide (08 marks)
iii. Carbon, silicon germanium and lead react with sodium hydroxide
(06 marks).
4 a). Explain what is meant by following terms:
i. Osmosis (03 marks)
ii. Osmotic pressure (03 marks)
b) State the significance of osmosis (02 marks)
c) Describe a method which can be used to determine the osmotic pressure
of a solution. (08 marks)
d) State the conditions under which solutions don’t obey the laws of
Osmotic pressure (03 marks)
e) The Osmotic pressure of a solution containing 1.24% of a polymer is 3.1
X 10-3 atmosphere at 25 °C. Determine the relative molecular mass of the
polymer (R=0.0821). (03 marks).
SECTION B
5. Complete the following equations and in each case outline a mechanism
for the reaction.
a) CH3CH2CH2Br + CH3CH2𝑂̅𝑁𝑎+ CH3CH2OH
(02 marks)
©DEPT. OF CHEMISTRY, BUSOGA COLLEGE MWIRI
2019
b) CH3CH=CHCH3 Cl2/H2O (04 marks )
c) -CH=CH2 H2SO4 /H2O (04 marks)
d) CH3C(OH)CH3 + Conc. H3PO4 Heat (04 marks)
e) -CH2Br + 𝑂̅𝐻 (aq) Heat (04 marks)
f) (CH3)2C=CH2 + I2 (aq) CCl4 (02 marks)
6. a). A solution containing 20.0g of a polymer X in 1 litre of a solvent
exerts an osmotic pressure of 1.4 mmHg at 25 °Ċ.
i. Calculate the molecular mass of polymer X (05 marks )
ii. The molecular formula of the monomer of X is (CH2CHCN).
Determine the number of monomer units in polymer X. (021/2
marks)
iii. Draw the general structural formula of polymer X (01 mark)
b) i). Describe how the molecular mass of a substance can be determined
by the freezing point depression method. (06 marks).
ii. Calculate the freezing point depression of the solvent in (a) above.
Given that the freezing point constant of the solvent is 5◦C per
litre. (03 marks)
7. Potassium manganate (VII) is not used as a primary standard in
volumetric analysis and has to be standardized.
a) i). What is meant by the term primary standard (02 marks)
ii. State three characteristics of a primary standard (03 marks)
iii. Name other substances other than ethanedioc acid, which can be
used as primary standard for potassium manganate (VII). (01 mark)
b) Explain why hydrochloric acid is not used to acidify solution of
potassium manganate (VII). (04 marks)
c) Acidified potassium manganate (VII) reacts with ethanedioc acid.
Write;
i. the half equations for the reaction (02marks)
ii. the overall equation for the reaction (2 marks)
d). 20.0 cm3 of 0.01 M manganate (VII) ion solution required exactly
16.65 cm3 of a solution containing 4.8g/l of an Oxalate
(CO𝑶− 𝑿+ ).2H2O. Calculate the atomic mass of element X.
©DEPT. OF CHEMISTRY, BUSOGA COLLEGE MWIRI
2019
8. a). The atomic number and atomic radii of some of the transition metals
are given in the table below
Element Sc Ti V Cr Mn Fe Co Ni Cu Zn
Atomic 21 22 23 24 25 26 27 28 29 30
number
Atomic 1.44 1.32 1.22 1.17 1.17 1.16 1.16 1.15 1.17 1.25
radii(Ȧ)
i. Plot a graph of atomic number against atomic radii (04 marks)
ii. Explain the shape of your graph (07 marks)
b) i). Write outer electronic configuration of manganese.(01 mark)
ii) state the possible oxidation states of manganese (021/2 marks)
iii. How does the acidity of the oxides of manganese vary with
increasing oxidation state? (01 marks)
iv. What is the change in the oxidation state when manganese (VII) is
reduced under alkaline conditions? (01 mark)
c. State four applications of potassium manganate(VII) in the
laboratory as an oxidizing agent (04 marks)
END
©DEPT. OF CHEMISTRY, BUSOGA COLLEGE MWIRI
2019
