BOTSWANA EXAMINATIONS COUNCIL
Botswana General Certificate of Secondary Education
CANDIDATE
NAME
CENTRE
NUMBER
CANDIDATE
NUMBER
CHEMISTRY
Paper 5
0570/05
Alternative to Practical
October/November 2013
1 hour
Candidates answer on the Question Paper.
No Additional Materials are required.
READ THESE INSTRUCTIONS FIRST
Write your Centre number, candidate number and name in the spaces provided at the top of this page.
Write in dark blue or black pen.
You may use a soft pencil for any diagrams, graphs or rough working.
Do not use staples, paper clips, highlighters, glue or correction fluid.
Answer all questions.
Write your answers in the spaces provided on the question paper.
Show your working for any calculations.
You may use a calculator.
The number of marks is given in brackets [ ] at the end of each question or part question.
A copy of the Periodic Table is printed on page 8.
For Examiner’s Use
1
2
3
Total
This document consists of 8 printed pages.
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For
Examiner’s
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2
1
A student was asked to find the mass of potassium hydroxide dissolved in 1 dm3 of solution
by titration with 0.102 mol / dm3 sulphuric acid. The acid was placed in a burette and
titrated with 25.0 cm3 of the potassium hydroxide solution containing a few drops of methyl
orange indicator in a conical flask.
The diagrams show parts of the burettes at the beginning and at the end of four titrations.
1st titration
0
1
2
17
18
19
2nd titration
15
16
17
3rd titration
35
4th titration
39
32
21
14
36
40
33
15
22
34
37
41
16
23
3
(a) (i) Use the burette diagrams of the four titrations to complete the table.
titration
1st
2nd
3rd
4th
final burette reading / cm3
initial burette reading / cm3
volume of acid used / cm3
tick () the best titration results
[7]
(ii) Use the ticked values to calculate the average volume of sulphuric acid used.
average volume = ....................... cm3 [1]
(b) Calculate the number of moles of sulphuric acid contained in the average
titration volume.
number of moles = ....................... moles [1]
© BEC 2013
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(c) The equation for the reaction is,
2KOH(aq) + H2SO4(aq)
(i)
K2SO4(aq) + 2H2O(l).
Use your answer to (b) and the equation to calculate the number of moles of
potassium hydroxide in 25 cm3.
number of moles = ....................... moles [1]
(ii) Use your answer to (c)(i) to calculate the number of moles of potassium
hydroxide dissolved in 1 dm3.
number of moles = ....................... moles [1]
(iii) Calculate the mass of potassium hydroxide dissolved in 1 dm3.
mass = ....................... g [1]
(d) One of the titration results was anomalous.
Suggest how a mistake in the way that the student carried out the titration of the acid
with the alkali led to this.
............................................................................................................................................
........................................................................................................................................[1]
[Total: 13]
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0570/05/O/N/13
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4
2
Tests were carried out on solid R. The table shows some tests, observations and conclusions
drawn. Complete the table.
(a) (i)
test
observations
conclusions
A sample of solid R was
placed in a dry boiling
tube and gently heated.
........................................
Water of crystallisation
is lost.
................................... [1]
Solid R changed from
blue to white.
(ii)
Whilst the boiling tube
was cooling, another
sample of solid R was
placed into another
boiling tube and then half
filled with water. This
was divided into four
portions which were
used for tests (b) to (e).
(iii)
To the solid in (a)(i),
about two to three drops
of water were added to
the boiling tube,
The solid turned from
white to blue.
......................................
......................................
................................. [1]
(iv)
and then, excess water
was added and the
mixture was shaken.
........................................
Solid R was soluble.
........................................
........................................
................................... [2]
(b) (i)
To the first portion,
aqueous sodium
hydroxide was added
drop by drop until there
was a change,
........................................
Cu2+ ions are
suspected.
........................................
........................................
................................... [2]
(ii)
© BEC 2013
then, excess sodium
hydroxide was added to
the mixture in (b)(i).
........................................
....................................[1]
0570/05/O/N/13
Cu2+ ions present
For
Examiner’s
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5
(c) (i)
To the second portion
aqueous ammonia was
added drop by drop until
a change was seen,
........................................
Cu2+ ions suspected to
be present.
........................................
................................... [1]
(ii)
then, excess aqueous
ammonia was added to
the mixture in (c)(i).
........................................
Cu2+ ions confirmed to
be present.
........................................
........................................
....................................[2]
(d)
To the third portion,
........................................
........................................
........................................
........................................
........................................
........................................
was added.
[1]
........................................
SO42− ions present
....................................[2]
(e)
To the fourth portion,
aqueous sodium
carbonate was added
until there was no further
change. The mixture
was left to stand for
about 2 minutes.
........................................
An insoluble carbonate
is formed
........................................
........................................
........................................
................................... [2]
(f) Suggest the name and formula of solid R.
Name .................................................................................................................................
Formula .........................................................................................................................[2]
[Total: 17]
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0570/05/O/N/13
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6
3
A student is making a sample of magnesium sulphate crystals.
•
•
•
The student measures out a sample of powdered magnesium into a beaker, she places
the beaker in a fume cupboard and then adds a small quantity of dilute sulphuric acid.
When the reaction has finished some magnesium remains in the beaker.
She separates the excess magnesium from the solution.
Then she obtains magnesium sulphate crystals from the solution.
The diagrams show the balance windows when measuring the powdered magnesium.
25
31
26
32
27
33
28
34
29
empty beaker
beaker containing
powdered magnesium
(a) (i) Record the balance readings.
mass of beaker only
....................... g [1]
mass of beaker and magnesium
....................... g [1]
(ii) Calculate the mass of magnesium in the beaker.
mass of magnesium = ....................... g [1]
(b) The student added enough sulphuric acid to dissolve most of the magnesium, so that
no acid was left over.
State one method that she can use to separate the excess magnesium from the solution.
........................................................................................................................................[1]
(c) Briefly explain how the student can obtain hydrated magnesium sulphate crystals
from the solution.
............................................................................................................................................
............................................................................................................................................
........................................................................................................................................[2]
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(d) Suggest one safety precaution that should be observed when reacting the magnesium
with sulphuric acid.
............................................................................................................................................
........................................................................................................................................[1]
Explain your answer.
............................................................................................................................................
........................................................................................................................................[1]
(e) Hydrated magnesium sulphate has the formula MgSO4.6H2O.
Suggest the approximate mass of crystals that the student will obtain if she follows the
method you have explained in part (c).
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
........................................................................................................................................[2]
[Total: 10]
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© BEC 2013
0570/05/O/N/13
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8
© BEC 2013
0570/05/O/N/13
For
Examiner’s
Use