Page 102 - Science Coursebook

7.4 Forming salts by neutralisation

You will remember that alkalis react with acids and neutralise them. When an acid
is neutralised by an alkali, a salt is produced. For example, when sodium hydroxide
reacts with hydrochloric acid, the salt sodium chloride is formed. The other product is
water.
sodium hydroxide + hydrochloric acid → sodium chloride + water

The general equation for neutralisation reactions is:
acid + alkali → salt + water

Questions

1 How can you test to see if a liquid is an acid or an alkali?
2 What word is used to describe a solution that is neither acid nor alkaline?
3 What are the properties of alkalis?

Activity 7.4
Preparing a salt by neutralisation

SE 1 Place hydrochloric acid in a burette. step 3
2 Measure out 20 cm of sodium hydroxide
3
in a small flask.

3 Add a few drops of Universal Indicator
solution. dilute
4 Add the acid from the burette slowly, hydrochloric
swirling the flask (moving it gently round) acid

as you add the acid.
5 When the Universal Indicator changes Universal
to green you have produced a neutral Indicator
solution. dilute sodium
6 Add a spatula of charcoal powder to the hydroxide
green solution. Mix it with a glass rod.
The charcoal takes the green colour of the
Universal Indicator out of the solution. step 6
7 Filter the mixture.
8 Place the filtrate into an evaporating dish neutral

and heat gently. solution
Safety: Take care as the solution may spit
and burn you. charcoal powder
9 Stop heating when you see some crystals mixed in
around the edge of the solution.
10 Leave the evaporating basin for a few days.
The water will evaporate slowly, leaving
crystals of the salt.
continued ...

100 7 Salts