GCE 'O' 2010 Science (Chemistry) Preparation list
Thursday, October 21, 2010
GCE 'O' 2010 Science (Chemistry) Paper 5
8:00 AM Unknown
You are provided with a sample of solid salt,
X, in a large stoppered test-tube. Solid X is a corrosive and
so should not be touched.
Carry out the following experiments and test
any gases evolved. Carefully record your observations.
The volumes given below, unless referring to
drops of solution, are approximate and should be estimated rather than
measured.
test
|
observations
|
|
(a)
|
Dissolve the solid
salt X, in the large test-tube, in
distilled water and then add more distilled water until the test-tube is
about two-thirds full. Stopper and shake the test-tube thoroughly.
You will use this solution in parts (b) and (c).
|
Orange/Yellow solution formed
When orange
solution dissolved in distilled water.
[1]
|
(b)
|
Place 4cm3
of solution from part (a) in a clean test-tube.
To this
test-tube, add 4cm3 of dilute sulfuric acid and 3-4 pieces of
granulated zinc. Gently warm, but do not boil, this mixture.
Leave this test-tube to stand in the
test-tube rack.
Keep this mixture for use in parts (d) and
(e).
Only proceed to part (d) when no further
changes are observed in this test-tube.
While you are waiting, continue with part (c).
|
Bubbles of gas occur, orange solution turns yellow
After 20min, the yellow solution turns colourless.
Use lighted wooden splint to test for ‘pop’ sound. Hydrogen gas evolved.
[3]
|
(c)
|
(i) Place 2cm3 of the solution from part
(a) in a clean test-tube.
To this
test-tube, add dilute sodium hydroxide solution dropwise, with shaking, until
no further change is observed.
|
Reddish/ orange brown ppt formed which is insoluble in excess formed |
(ii) Place 2cm3 of the solution from part
(a) in a clean test-tube.
To this
test-tube, add 1-2 drops of solution Y.
|
Reddish brown solution formed.
The yellow solution turns orange/ darker. |
|
(iii) Place 2cm3 of the solution from part
(a) in a clean test-tube.
To this
test-tube, add 5-10 drops of aqueous silver nitrate.
Now add dilute
aqueous ammonia dropwise, with shaking, until no further change is observed.
|
White / Light yellow ppt formed.
White ppt dissolve on adding aq ammonia.
Reddish brown/ white ppt formed insoluble in excess ammonia
[4]
|
(d)
|
Using a teat
pipette, remove 1-2cm3 of the solution from part (b) in a clean
test-tube.
To this
test-tube, immediately add dilute sodium hydroxide solution dropwise,
with shaking, until no further change is observed.
Carry on with part
(e), but contimue to observe this test-tube for several minutes.
|
Dark/ dirty green ppt formed.
Affter sometimes, reddish brown ppt is formed at the sides of test-tube
[2]
|
(e)
|
Using a teat
pipette, remove 1-2cm3 of the solution from part (b) in a clean
test-tube.
To this
test-tube, immediately add 1-2 drops of solution Y.
|
Reddish brown solution formed.
The orange solution turns pale yellow
[1]
|
Conclusions
Consider the
results of the experiments in parts (b) to (e).
Give four
different conclusions about the observations you have made in parts (b) to (e).
You are not
expected to make any conclusions about solution Y.
Give evidence (a
reason) to support each of your conclusions.
Conclusion 1 …Zinc
displaces the less reactive metal from the solution of X…...……………
Evidence 1 …..Grey
solid of the metal from X seen in (b). White ppt of zinc hydroxide seen in (d).……………………………………..…………………………………………………………...
Conclusion 2 …Redox
reaction takes place in (b).………………………………………………
Evidence 2 ……Zinc
is oxidized while salt X is reduced as seen in the vigorous reaction in (b) and
the evolution of gas………………………………………………………………………...
Conclusion 3 …Salt
X contains a chloride……………………………….. ………………………
Evidence 3 ……The
white ppt formed with silver nitrate solution in c(iii)….……………...…...
Conclusion 4 …Salt
X contains iron (III) ions..……………………………………………………
Evidence 4 …..The
reddish brown ppt formed with sodium hydroxide solution in c(i)……..[4]
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