LEARNING TARGETS

Describe the properties of acids and bases and apply methods, e.g. indicators, to identify familiar materials as acids, bases, or neither

Write balanced word and chemical equations for basic acid reactions (neutralization, metals, oxides and carbonates)

In 1884 Swedish scientist Svante Arrhenius came up with the definition of an acid as a material that can release a proton or hydrogen ion (H ⁺). Hydrochloric acid in solution ionizes and becomes hydrogen ions and chloride ions.

A base (or alkali), is a material that can donate a hydroxide ion (OH^-). Sodium hydroxide in water solution becomes sodium ions and hydroxide ions.

Reactions of acids with bases

A chemical reaction happens if you mix together an acid and a base. The reaction is called neutralisation, and a neutral solution is made if you add just the right amount of acid and base together.

Metal oxides and metal hydroxides

Metal oxides and metal hydroxides are two types of bases. For example copper oxide and sodium hydroxide.

Here are general word equations for what happens in their neutralisation reactions with acids.

metal oxide + acid → a salt + water

metal hydroxide + acid → a salt + water

Notice that a salt and water are always produced. The mixture usually warms up a little during the reaction, too. The exact salt made depends upon which acid and base were used.

Carbonates and hydrogen carbonates

Carbonates and hydrogen carbonates are two other types of base. They also make a salt and water when we neutralise them with acid. But this time we get carbon dioxide gas too.

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.

These are the general word equations for what happens:

acid + metal carbonate → a salt + water + carbon dioxide

acid + metal hydrogen carbonate → a salt + water + carbon dioxide

Neutralization is a chemical reaction in which an acid and a base react with each other. In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in solution. Therefore complete neutralization will lead to a solution with a pH of 7.

Using neutralisation

• 1. Farmers use lime (calcium oxide) to neutralise acid soils.

  2. Your stomach contains hydrochloric acid, and too much of this causes indigestion. Antacid tablets contain bases such as magnesium hydroxide and magnesium carbonate to neutralise the extra acid.

  3. Bee stings are acidic. They can be neutralised using baking powder, which contains sodium hydrogen carbonate.