GCE 'O' 2014 Science (Chemistry) Paper 5
You
are provided with two solid samples of salt
Q, one in a small stoppered hard
glass test-tube and another is in a large
stoppered test-tube.
You
are also provided with a solution R.
Carry
out the following experiments. Carefully record your observations.
You
should test any gases evolved.
The
volumes given below are approximate and should be estimated rather than
measured.
test
|
observations
|
|
(a)
|
Remove the stopper from the small hard glass test-tube, labelled salt Q.
Heat this test-tube gently at first and then strongly
for about 1 minute. During this stage you may observe water droplets being
formed on the sides of the test-tube.
|
White solid
decomposes to give a colourless solution.
Upon
further heating, colourless solution turns into white solid.
Orange-brown
gas is evolved.
|
Continue to heat strongly until no further changes
are seen. This should take at least another minute.
While heating strongly,
test any gases evolved using litmus paper and a glowing splint.
|
Blue litmus
paper turns red.
Glowing
splint continues to glow.
(Need to do it slowly)
|
|
Remove the stopper from the large test-tube labelled salt
Q. Add about 10cm3 of deionized water to sample in the large test-tube. Shake the mixture.
This solution is Q(aq).
|
||
(b)
|
Place about 2cm3 of Q(aq)
into a clean test-tube.
Add a few drops of dilute sodium hydroxide, shaking
the test-tube between each addition.
Add a further 2cm3 of dilute sodium
hydroxide and shake the mixture.
Add 2 pieces of aluminium foil to the test-tube and gently warm the mixture.
|
White ppt is observed in Aq NaOH is
added.
White ppt is insoluble in excess.
Red litmus turns blue, NH3 gas is
evolved.
|
(c)
|
Place about 1cm3 of Q(aq) into a clean test-tube.
Add about 1cm3 of aqueous ammonia slowly,
with shaking, until no further change is seen.
|
No ppt is formed.
Solution remains colourless.
(add 1ml
will do)
|
Solution R
has been prepared for you by adding water to the final solid product from
heating salt Q in part (a). The mixture was the heated and filtered.
In part (d),
you are going to use the carbon dioxide generator, shown in Fig. 1.1, to
bubble CO2 through solution
R.
To assemble the carbon dioxide generator, cover the
marble chips with dilute hydrochloric acid and insert the bung and the
delivery tube. Bubbles of carbon dioxide will be produced.
 |
||
test
|
observations
|
|
(d)
|
Place about 2cm3 of solution R into a clean test-tube.
Use the carbon dioxide generator to bubble CO2
through solution R until no
further changes are seen. This produces solution S.
Note: If the delivery of CO2 bubbles slows down, pour away the used acid
and replace it with dilute hydrochloric acid.
|
White ppt is observed in solution R.
Upon further bubbling, white ppt gives a colourless
solution.
|
Remove the test-tube containing solution S from the delivery tube.
Gently heat solution S until it starts to boil.
|
Upon heating, colourless solution turns to give a
white ppt.
|
Conclusions
(e) Suggest an identity for the cation and for the anion in salt Q.
(e) Suggest an identity for the cation and for the anion in salt Q.
Give evidence to
support each of your suggestions.
cation is …................…...….......................................................................…………
evidence .…...............…………………………………….............................................
.………………………………............................……………….………….......
………………………………............................…………………….....……...
.………………………………............................……………….………….......
………………………………............................…………………….....……...
anion is …..........................................……………………………………….....………
evidence .…...............…………………………………….............................................
………………………………............................………………….……….......
………………………………............................…………………………....[2]
(f) Consider the results of the experiments you have performed.
Give
two further conclusions about the
chemistry, ions or gases involved in these reactions.
Give evidence to support each of your conclusions.
conclusion 1 …................…...….......................................................................…………
evidence …...............……………………………………..............................................
………………………………............................……………….………….......
………………………………............................…………………….....……...
conclusion 2 …..........................................……………………………………….....………
evidence .…...............…………………………………….............................................
………………………………............................………………….……….......
………………………………............................…………………………....[2]
