P525/3
CHEMISTRY
Paper 3
FEB-MAR
3 ¼ hours
Uganda Advanced Certificate of Education
CHEMISTRY PRACTICAL
(Principal Subject)
Paper 3
3 hours 15 minutes
INSTRUCTIONS TO CANDIDATES:
This paper consists of three compulsory questions.
Answer all questions in the spaces provided
Mathematical tables (3 – figure tables) are adequate or non-programmable
scientific electronic calculators may be used
QNS MARKS
1
You are provided with the following
BA1 which is solution mixture containing sodium carbonate and
sodium hydroxide solution.
BA2 which is 0.1M hydrochloric acid.
Phenolphthalein and methyl orange indicator.
You are required to determine the concentration of Na2CO3 and
NaOH in the solution mixture and hence the percentage of Na2CO3
in the mixture.
Procedure I
(i) Pipette 20 or 25cm3 of BA1 into a clean conical flask, add 2-3 drops
of phenolphthalein indicator and titrate with BA2 from the burette
until the end point.
(ii) Repeat the titration until you obtain consistent results.
(iii) Record your result in the table 1 below.
Results.
Volume of pipette used …………………………………………..(½marks)
Table 1. With phenolphthalein indicator
EXPERIMENT I II III
Final burette reading
(cm3)
Initial burette
reading(cm3)
Volume of BA2 used (cm3)
(4½marks)
Titre values used to calculate average volume of BA2 used are;
……………………………………… and……………………….cm3 .(½marks)
Therefore average volume of BA2using phenolphthalein
=…………………………………………………………… cm3. (2½marks)
2
Procedure II
(i) Pipette 20 or 25cm3 of BA1 into a clean conical flask. Add 2-3 drops
of methyl orange indicator and titrate with BA2 from the burette
until the end point is reached.
(ii) Repeat the titration until you obtain consistent results.
(iii) Record your results in the table 2 below.
Volume of pipette used ………………………………………………(½marks)
Table 2. With methyl orange indicator.
EXPERIMENT I II III
Final burette reading (cm3)
Initial burette reading(cm3)
Volume of BA2 used (cm3)
(4½marks)
Titre values used to calculate average volume of BA2 used are;
(½marks)
………………………………….and …………………………………..cm3
Therefore average volume of BA2using methyl orange =
………………………………………………………………………cm3. (2½marks)
(a)Write equation(s) that took place when using;
(i) Phenolphthalein indicator.
(1mark)
…………………………………………………………………………………………
…………………………………………………………………………………………
(ii) Methyl orange indicator.
(3mark)
……………………………………………………………………………………
…………………………………………………………………………………..
3
(b) Determine the volume of hydrochloric acid in BA2 required for the
neutralization of;
(i) Sodium carbonate.
(1mark)
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(ii)Sodium hydroxide.
(1mark)
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
(c) Calculate the concentration of sodium hydroxide in grams dm-3
in BA1
(5mark)
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(d) Calculate the concentration of sodium carbonate in grams dm-3 in BA1.
(5mark)
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
….………………………………………………………………………………..
……………………………………………………………………………………
4
(e) Determine percentage of sodium carbonate in the solution mixture.
(1½mark)
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
2. You are provided with substance Q which contains two cations and two
anions. You are required to carry out the following tests on Q and identify
the cations and anions in Q. Record your observations and deductions in
the table below. (30marks)
Tests Observations Deductions
(a) Heat a
spatula endful
of Q in dry test
tube.
(b) Shake two
spatula endful
of Q with about
5cm3 of water
and filter. Keep
both the filtrate
and residue.
Divide the
filtrate into six
parts.
(i) To the first
part of the
filtrate, add
dilute sodium
hydroxide
5
solution drop
wise until in
excess.
(ii) To the
second part of
the filtrate, add
ammonia
solution drop
wise until in
excess.
(iii) To the third
part of the
filtrate, add 2-
3drops of dilute
sulphuric acid.
(iv) To the fourth
part of the
filtrate, add 2-
3drops of
potassium
chromate (VI)
and then add
dilute sodium
hydroxide
solution drop
wise until in
excess and allow
the mixture to
stand.
(v) To the fifth
part of the
filtrate, add 2-3
drops of lead (II)
nitrate solution,
heat and allow
to cool.
(vi) Use the sixth
part of the
filtrate to carry
out a test of
6
your own choice
to confirm one
of the anions in
Q.
(c) Wash the
residue with
water and
transfer it to the
test tube, add
dilute nitric acid
drop wise until
the residue
dissolves. Divide
the solution into
five portions.
(i) To the first
part of the
solution, add
dilute sodium
hydroxide
solution drop
wise until in
excess.
(ii) To the
second part of
the solution,
add ammonia
solution drop
wise until in
excess.
(iii) To the third
part of the
solution, add 2-
3drops of dilute
sulphuric acid.
(iv) To the fourth
part of the
solution, add 2-
3 drops
potassium
7
chromate (VI)
solution and
then add
sodium
hydroxide
solution
dropwise until
in excess.
(v) To the fifth
part of the
solution, carry
out a test of
your own choice
to confirm the
second cation in
Q
(d) Identify
(i) cations in Q……………………………and…………………………………….
(ii) anions in Q……………………………and……………………………………..
8
Confidential
Q- PbCO3:BaCl2 ratio 2:1
BA1 - which is solution mixture containing sodium carbonate and sodium
hydrogen carbonate solution (
5.3g of Na2CO3 and 2.8g of NaOH in one litre
BA2- 0.1M hydrochloric acid
Provide each student with;
- 100cm3 of BA1
- 100cm3 of BA2
- Access to heat source,
- Bench reagents.
