Answers:
LEVEL: AS
CHEMISTRY – Inorganic Chemistry
9. Reactions of halogens and halides (15 minutes)
(a) Describe what you would do to show that a sample of drinking water was contaminated with
iodide ions. What would you see?
(3 marks)
Acidify the sample with dilute nitric acid then add drops of aqueous silver nitrate. A yellow precipitate
(of silver iodide) will form.
(b) Describe what you would observe when small samples of solid sodium chloride, solid
sodium bromide and solid sodium iodide are warmed separately with concentrated sulphuric
acid.
Sodium chloride:
(1 mark)
A colourless, sharp-smelling gas is given off, which forms steamy fumes in moist air.
Sodium bromide:
(2 marks)
The colourless mixture turns to a brown liquid and a gas, with a choking smell and a colour varying
from pale yellow to dark red-brown, is given off, which forms steamy fumes in moist air.
Sodium iodide:
(2 marks)
The colourless mixture turns to a dark brown liquid and a grey metallic-like solid higher in the tube. A
gas with a bad-egg smell is given off, together with a purple vapour and a gas that forms steamy fumes
in moist air.
(c) The reaction of chlorine with aqueous sodium hydroxide under different conditions is
represented by the following ionic equations:
With cold dilute sodium hydroxide:
Cl2 (g) + 2OH−(aq) → Cl−(aq) + ClO−(aq) + H2O(l)
With hot concentrated sodium hydroxide:
3Cl2 (g) + 6OH−(aq) → 5Cl−(aq) + ClO3−(aq) + 3H2O(l)
(i) What type of reaction is represented by the above ionic equations?
(1 mark)
Redox (reduction/oxidation).
Copyright © Pearson Education Limited 2001
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Answers:
LEVEL: AS
CHEMISTRY – Inorganic Chemistry
(ii) Give the name of the oxo anions of chlorine formed in the reactions.
(2 marks)
CIO−
−
CIO3
chlorate(T) (hypochlorite);
chlorate(V)
(iii) Give one everyday use for each of the following reaction products:
NaClO
(1 mark)
Sterilizing and bleaching agent.
NaClO3
(1 mark)
Weed-killer.
(d) Fluorine is the first member of group VII. Some of its properties are different from those of
the other halogens. Illustrate two of these differences by reference to:
(i) The acidity of the aqueous hydrogen halides.
(1 mark)
Hydrogen fluoride gives a weak dimeric acid in aqueous solution but the other hydrogen halides give
–
strong monmeric acids: H2F2(aq) → H+aq) + HF2 (aq).
(ii) The solubilities of the silver halides.
(1 mark)
Silver fluoride is soluble in water but the other silver halides are sparingly soluble salts, becoming
progressively less soluble from AgCl to AgI.
(Total marks 15)
Copyright © Pearson Education Limited 2001
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