Answers to end-of-chapter
questions
Chapter 5 Acids, bases and salts
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4
a pH 3
[1]
b Add blue (or neutral) [1] litmus [1]; if it
turns red, it is acidic [1].
[3]
c i calcium carbonate + hydrochloric acid →
calcium chloride + carbon dioxide + water
[1 mark for each product]
[3]
ii in a blast furnace for producing iron
[1]
iii lime/calcium oxide, or slaked lime/
calcium hydroxide
[1]
[2]
d Fe + 2HCl → FeCl2 + H2
[Total = 11]
5
a acidic: < 7, any appropriate e.g. SO2
basic: > 7, any appropriate e.g. CaO
neutral: 7, any appropriate e.g. H2O
[6]
b i an oxide/substance that will react with/
dissolve in both acids and alkalis.
[1]
ii any strong acid (e.g. HCl) + any strong
alkali (e.g. NaOH)
[2]
[Total = 9]
6
Step 2: Filter to remove excess solid
[1]
Step 3: Evaporate to crystallisation point
[1]
Step 4: Leave solution to cool [1]; dry crystals
on filter paper [1]
[2]
[Total = 4]
7
a first row: sodium hydroxide; nitric acid
[2]
second row: copper oxide
[1]
third row: silver nitrate; hydrochloric acid
(or soluble chloride salt)
[2]
fourth row: zinc sulfate
[1]
[2]
b i Ag+(aq) + Cl−(aq) → AgCl(s)
ii ZnCO3 + H2SO4 → ZnSO4 + CO2 + H2O [2]
[Total = 10]
The process of dissolving takes place when the
molecules of water are able to break up the lattice
structure of the ions in the solid salt. If the bonding
between the ions in the solid is too strong, then
the water molecules are not able to break up the
structure. The strength of the bonding in an ionic
solid depends on the size and charge of the ions.
There are some guidelines that help us know which
salts are soluble in water and which are not.
2
In understanding the different uses of the word
‘strong’ in these cases, we have to focus on the way
the adjective is being applied.
In the first case, the term is being applied to the
solution – ‘the coffee is strong’ means that it is
concentrated. A weak cup of coffee would have a
low concentration of coffee.
In the second case, the word is applied to the nature
of the acid itself – not the solution – the strong acid
is fully ionised in water. It is therefore possible to
have a dilute solution of a strong acid.
Remember, in chemistry, to use the words
‘concentrated’ and ‘dilute’ when talking about how
concentrated a solution is.
3
a pH 11
[1]
b slaked lime
[1]
c i to help plants grow better (or words to
that effect)
[1]
ii sulfur dioxide [1] from power stations [1]
or nitrogen oxides [1] from car exhausts
[1]; dissolves in rain [1]
[3]
d i neutralisation
[1]
ii Measure the calcium hydroxide/alkali with
a pipette [1], add indicator [1] and add
acid from burette until there is a colour
change [1].
[3]
[Total = 10]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 5
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