A chemical reaction happens if you mix together an acid and a base. The reaction is called neutralisation. A neutral solution is made if you add just the right amount of acid and base together. Neutralisation is an exothermic reaction, so the reaction mixture warms up during the reaction.
Metal oxides act as bases. Here is the general word equation for what happens in their neutralisation reactions with acids:
metal oxide + acid → a salt + water
The salt made depends on the metal oxide and the acid used. For example, copper chloride is made if copper oxide and hydrochloric acid are used:
copper oxide + hydrochloric acid → copper chloride + water
CuO + 2HCl → CuCl2 + H2O
Metal hydroxides act as bases. Some of them dissolve in water, so they form alkaline solutions. Here is the general word equation for what happens in their neutralisation reactions with acids:
metal hydroxide + acid → a salt + water
As with metal oxides, the salt made depends on the metal hydroxide and the acid used. For example, sodium sulfate is made if sodium hydroxide and sulfuric acid are used:
sodium hydroxide + sulfuric acid → sodium sulfate + water
2NaOH + H2SO4 → Na2SO4 + 2H2O
Notice that a salt plus water are always produced when metal oxides or metal hydroxides react with acids.
Most carbonates are usually insoluble (they do not dissolve in water). They also neutralise acids, making a salt and water, but this time we get carbon dioxide gas too.
Here is the general word equation for what happens:
metal carbonate + acid → a salt + water + carbon dioxide
The reaction fizzes as bubbles of carbon dioxide are given off. This is easy to remember because we see the word 'carbonate' in the chemical names. For example, copper carbonate reacts with nitric acid:
copper carbonate + nitric acid → copper nitrate + water + carbon dioxide
CuCO3 + 2HNO3 → Cu(NO3)2 + H2O + CO2
Here are some ways neutralisation is used: