GCE 'O' 2008 Science (Chemistry) Paper 5
You
are provided with a sample of solid salt, T, which contains the element
K, Br and O only.
Carry out the following experiments and carefully record your observations.
The
volumes given below, unless referring to drops of solution, are approximate and
should be
estimated rather than measured.
(a)
Adjust the Bunsen
burner to give a blue flame. Moisten the end of a wooden splint with
water and dip the moist end of the splint into the sample of solid T.
Record
your observations.
Observations ...................................................................................................................................... [1]
Carry
out the following tests on salt T. Record your observations in the
spaces provided.
(b)
Test
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observations
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Use the smaller tip
of a spatula to transfer a small
sample of solid T into a clean and
dry hard-glass test-tube.
Heat the sample carefully
until it has melted completely;
then heat the sample strongly
until no further changes are seen.
Test any gas
evolved using a
glowing splint.
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[4]
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Leave the test-tube used in part (b) cool. Keep the test-tube and its contents for use in part (c); only proceed to part (c) when this test-tube is cool.
(c)
(i)
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Dissolve the
residue in the cool test-tube from part (b) in distilled water
and then continue adding water until the test-tube is half full.
Stopper and shake
the test-tube thoroughly.
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(ii)
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Place 2cm3 of the
solution from part (c)(i) in a clean test-tube.
Add 2cm3 of dilute
HNO3 and shake the test-tube.
Then add, with
shaking, 10 drops of KI solution.
Then add 2 to 4
drops of starch solution and
shake the
test-tube.
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(iii)
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Place 2cm3 of the
solution from part (c)(i) in a
clean, dry
test-tube.
Add 5 drops of
aqueous AgNO3.
Then add, with
shaking, about 2cm3 of dilute
aqueous ammonia
solution.
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(d)
Use a spatula to
transfer a small sample of solid T into
a clean, dry test-tube and dissolve it in about 2cm3 of
distilled water.
To this test-tube,
add 5 drops of aqueous AgNO3, followed by
1cm3 of dilute aqueous ammonia, with
shaking.
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Conclusions
Consider the results of the experiments in parts (b),
(c) and (d). State at least four conclusions you can draw
about the chemical reactions involved.
