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Science

Acids and bases

Neutralisation

When an alkali is added to an acid the pH of the mixture rises. This is because the alkali reacts with the acid to form neutral products. The reverse situation also happens too: when an acid is added to an alkali the pH of the mixture falls. This is because the acid reacts with the alkali to form neutral products.

A reaction in which acidity or alkalinity is removed is called neutralisation. A neutralisation involving an acid and a base (or alkali) always produces salt and water.

acid + base → salt + water

Hydrogen ions and pH

In all solution, all acids contain hydrogen ions, H+. The greater the concentration of these hydrogen ions, the lower the pH.

Naming salts

The name of the salt produced in a neutralisation reaction can be predicted. The first part of the name is ‘ammonium’ if the base used is ammonia. Otherwise, it is the name of the metal in the base. The second part of the name comes from the acid used:

  • chloride, if hydrochloric acid is used
  • nitrate, if nitric acid is used
  • sulfate, if sulfuric acid is used
  • phosphate, if phosphoric acid is used.

The table shows some examples.

Examples

acid+basesalt + water
hydrochloric acid+copper oxidecopper chloride + water
sulfuric acid+ sodium hydroxidesodium sulfate + water
nitric acid+calcium hydroxidecalcium nitrate + water
phosphoric acid+iron(III) oxideiron(III) phosphate + water

Carbonates and acids

Carbonates also neutralise acids. As well as a salt and water, carbon dioxide is also produced. The name of the salt can be predicted in just the same way.

For example:

hydrochloric acid + potassium carbonate → potassium chloride + water + carbon dioxide

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