1.1 The state symbols in equations are (s), ( l ), (g) and (aq).
1.1.1 Soluble salts can be made from acids by reacting them with: metals – not all are suitable;
insoluble bases – the base is added to the acid until no more will react and the excess solid
is filtered off; alkalis – an indicator can be used to show when the acid and alkali have
completely reacted to produce a salt solution.
126.96.36.199 Salt solutions can be crystallised to produce solid salts.
188.8.131.52.1 Insoluble salts can be made by mixing appropriate solutions of ions so that a
precipitate is formed, from the reacion of two soluble salts. Precipitation can be used
to remove unwanted ions from solutions, for example in treating water for drinking or in
2 C2.6.2 Acids And Bases
2.1 Substances with a pH of less than 7 are acids.
The more strongly acidic the solution, the lower its
pH number. Acidic solutions turn blue litmus
paper red. They turn universal indicator paper red
if they are strongly acidic, and orange or yellow if
they are weakly acidic.
2.1.1 Substances that can react with acids and
neutralise them to make a salt and water are
called bases. They are usually metal oxides or
metal hydroxides. Bases which dissolve in
water are also called alkalis.
184.108.40.206 Alkaline solutions have a pH of more
than 7. The stronger the alkali, the
higher the pH number. Alkalis turn red
litmus paper blue. They turn universal
indicator paper dark blue or purple if
they are strongly alkaline, and
blue-green if they are weakly alkaline.
220.127.116.11.1 Neutral solutions have a pH of 7. They do not
change the colour of litmus paper, but they turn
universal indicator paper green. Water is neutral.
18.104.22.168.1.1 The particular salt produced in any
reaction between an acid and a base
or alkali depends on: the acid used
and the metal in the base or alkali.
22.214.171.124.1.1.1 Ammonia dissolves in water to
produce an alkaline solution. It is
used to produce ammonium salts.
Ammonium salts are important as
126.96.36.199.188.8.131.52 Hydrogen ions, H+(aq), make solutions
acidic and hydroxide ions, OH–(aq),
make solutions alkaline. The pH scale is
a measure of the acidity or alkalinity of a
184.108.40.206.220.127.116.11.1 In neutralisation reactions, hydrogen ions react with hydroxide ions
to produce water. This reaction can be represented by the equation: