Page 103 - Science Coursebook

7.4 Forming salts by neutralisation

... continued
Questions
A1 What colour is the Universal Indicator solution in the sodium hydroxide?
A2 What colour is Universal Indicator solution in a neutral solution?
A3 Why do you need to swirl the flask as you add the acid?

A4 Imagine that you accidentally added too much acid from the burette. What
could you do to form a neutral solution?
A5 What salt is formed in this reaction?
A6 Write the word equation for this reaction.
A7 Describe the salt crystals you obtained.

Alkalis and bases
When a metal oxide dissolves in water, it forms an alkaline solution. Metal oxides are
called bases. Soluble metal bases form alkalis when they dissolve in water.

For example:
sodium oxide + water → sodium hydroxide
Sodium oxide is a base. The sodium hydroxide is an alkali.

Some metal oxides are not soluble in water, for example iron oxide and copper oxide.
So they do not form alkalis. But – as you saw if you did activity 7.2B – they can still
react with acids to form salts.

copper oxide + sulfuric acid → copper sulfate + water

Questions

4 What is the difference between a base and an alkali?
A+I 5 Suggest how you could use iron oxide to make iron chloride.

Summary
• Salts are formed when an acid is neutralised by an alkali.
• Metal oxides are called bases.
• Soluble metal bases form alkalis.
• acid + alkali → salt + water

7 Salts 101