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545/3
Chemistry
Paper 3
2 Hours
MOCK EXAMINATIONS 2019
Uganda Certificate of Education
CHEMISTRY PRACTICAL
Paper 3
2 hours
INSTRUCTIONS TO CANDIDATES:
Answer all the questions.
All questions carry equal marks.
Answers are to be written in the spaces provided ONLY.
You are not allowed to use any reference books.
Mathematical tables, slide rulers and non-programmable silent electronic calculators
may be used.
You will be penalized for untidy work.
Q.1 Q.2 TOTAL
1. You are provided with the following:
BA1, which is a solution containing 3.8g of a metal hydroxide, M(OH)2
in 1dm3 of water.
BA2, which is hydrochloric acid of concentration 3.68 gdm-3
You are required to determine the atomic mass of M in M(OH)2
1
Procedure
Pipette 20.0 or 25.0 cm3 of BA1 into a clean conical flask, add 2-3 drops of methyl orange
indicator and titrate the contents with BA2 from the burette until the indicator changes colour.
Repeat the titration 2 -3 times to obtain consistent results. Record your results in the table
below.
Table of results:
Volume of pipette used………………………………………………………cm3
1 2 3
Final burette reading (cm3)
Initial burette reading(cm3)
Volume of BA2 used (cm3)
Titre values used for calculating the average volume of BA2 used:
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Average volume of BA2 used …………………………………………………… cm3
Question:
(a) Calculate the :
(i) Concentration of BA2 in moldm-3. (H=1, Cl=35.5)
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(ii). Number of moles of BA2 that reacted.
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2
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(iii). Number of moles ofBA1 that reacted with BA2.
( 2 moles of BA2 reacts with 1mole of BA1)
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(iv). Number of moles of M(OH)2 in 1dm3 of BA2.
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(b).Determine the;
(i). Formula mass of M(OH)2.
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(ii). Value of M in M(OH)2. (H=1,O=16)
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3
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2. You are provided with substance Q which contains two cations and one anion. Carry out the
following tests on Q to identify the cations and anion. Identify any gases evolved. Record your
results in the table below.
TESTS OBSERVATIONS DEDUCTIONS
(a) Heat one spatula endful of Q
in a dry test tube, first gently
then strongly until there is no further
change.
(b) To two spatula endfuls of Q in a
test tube, add about 5cm3 of dilute
nitric acid. To the resultant solution
add sodium hydroxide solution drop
wise until in excess and filter. Keep
both the filtrate and residue.
(c) To the filtrate from (b), add dilute
nitric acid drop wise until the
solution is just acidic. Divide the
resultant solution into two portions.
(i). To the first portion of the acidic
solution, add dilute sodium
hydroxide solution drop- wise until in
excess.
TESTS OBSERVATIONS DEDUCTIONS
4
(ii). To the second portion of the
acidic solution, add dilute ammonia
solution drop- wise until in excess
(d). Wash the residue from (b) and
dry it. Dissolve the dry residue in a
minimum amount of nitric acid.
Divide the resulting solution into
three portions
(i). To the first portion, add dilute
sodium hydroxide solution drop- wise
until in excess.
(ii). To the second portion, add
dilute ammonia solution drop- wise
until in excess.
(iii). To the third portion, add a
spatula endful of zinc powder and
shake. Allow to stand.
(e) (i) The cations in Q are:…………………………………and………………………………….
(ii) The anion in Qis:…………………………………………………………………………
END
