Neutralisation: acids, bases and salts
Neutralisation is a reaction between an acid and a base. An acid and a metal oxide or hydroxide make a salt and water. The acid and the metal in the base decide the name of the salt.
Practise acids and alkalis in pH Detective.
How to name a salt
The acid gives the second part of the salt name. Hydrochloric acid makes chlorides, sulfuric acid makes sulfates and nitric acid makes nitrates. The metal in the base gives the first part. For example, nitric acid and magnesium oxide make magnesium nitrate and water.
Bases that dissolve in water are called alkalis. Sodium hydroxide is an alkali, while copper oxide is an insoluble base. Both can react with acids to make salts and water.
Neutralisation and pH
Adding an alkali to an acid makes the solution less acidic, so its pH rises towards 7. If excess alkali remains, the pH can rise above 7. Explore acids, alkalis and indicators on the pH scale page.
In an acid and alkali reaction, hydrogen ions react with hydroxide ions to form water: H⁺(aq) + OH⁻(aq) → H₂O(l). This ionic equation describes that reaction, not every reaction between an acid and a base. Writing balanced ionic equations is Higher tier on AQA, Edexcel and OCR Gateway.
Other acid reactions
A metal carbonate reacts with an acid to make a salt, water and carbon dioxide. For example, calcium carbonate and hydrochloric acid make calcium chloride, water and carbon dioxide. See the tests for gases to find out how to identify carbon dioxide.
Some metals react with acids to make a salt and hydrogen. The reactivity series helps explain why metals react differently. The page on balancing equations shows how to count atoms on both sides of a symbol equation.
Common mistakes
- Calling every base an alkali. Only soluble bases are alkalis.
- Assuming every reaction mixture ends at pH 7. Excess reactant can remain.
- Using the metal to name the second part of the salt. The acid gives that part.
Find more topics in the chemistry hub.
Questions people ask
What does neutralisation make?
An acid reacting with a metal oxide or hydroxide makes a salt and water. An acid reacting with a metal carbonate also makes carbon dioxide.
Which salt does hydrochloric acid make?
It makes a chloride. The metal in the base gives the first part of the name.
Are all bases alkalis?
Only bases that dissolve in water are alkalis. Copper oxide is an insoluble base.