Page 99 - Science Coursebook

7.2 Preparing a salt using metal and acid

Using a metal oxide to make a salt
Some metals will not react with acids to make salts. For example,
silver and copper are too unreactive to displace hydrogen from
an acid.

So we have to find another way of making salts from unreactive
metals. We can do this by starting with a metal oxide.

Activity 7.2B
Making the salt copper sulfate

SE Safety: Remember not to boil the acid. Be careful when step 2
heating the evaporating basin as the solution may spit
and burn you. dilute
sulfuric
1 Pour about 100 cm of sulfuric acid into a 250 cm acid
3
3
beaker. Add black copper oxide powder to the acid in
the beaker. copper
2 Heat the mixture very gently, stirring all the time. oxide
Safety: Do not boil the mixture. Harmful fumes may

be given off.
3 When the mixture changes colour to blue turn off the

heat. Allow the mixture to cool.
4 Filter the mixture. The filtrate is a solution of copper

sulfate. Pour this into an evaporating basin. step 4
5 Heat the evaporating basin very gently until you see
crystals forming at the edge of the solution. Remove
from the heat and leave for a few days to form crystals.

Questions filtrate
A4 Suggest why the mixture was filtered.

A5 Suggest how you could use a similar method to
make copper chloride.

Summary
• Salts can be prepared by reacting metals with acids.
• To obtain a dry sample of the salt, you must allow the water to
evaporate from the solution of the salt.
• Unreactive metals will not react with acids, so you cannot make their
salts in this way.

7 Salts 97