Neutralisation Reactions

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What Is Neutralisation?

When acid meets base

Combustion

Neutralisation is a chemical reaction between an acid and a base. The acid and base react to produce two new substances: a salt and water. The solution becomes closer to neutral (pH 7) as the reaction proceeds.

The general word equation for neutralisation is:

For example, when hydrochloric acid reacts with sodium hydroxide (a base), the products are sodium chloride (common table salt) and water:

Notice that the salt is named from the metal in the base (sodium) and the non-metal part of the acid (chloride). This pattern works for all neutralisation reactions:

• Sulfuric acid + potassium hydroxide → potassium sulfate + water
• Nitric acid + calcium hydroxide → calcium nitrate + water

pH change during neutralisation

During neutralisation, the pH of the solution changes as the acid and base react. If you start with an acid and slowly add a base, the pH rises. If you start with a base and slowly add an acid, the pH falls. In both cases, the pH moves toward 7. When exactly the right amounts of acid and base have reacted, the solution is neutral (pH 7).

Antacids

Your stomach produces hydrochloric acid to help digest food. Sometimes too much acid is produced, causing heartburn and indigestion. Antacid tablets contain bases such as magnesium hydroxide, calcium carbonate or sodium bicarbonate. When you swallow an antacid, the base neutralises the excess stomach acid, forming salt and water and raising the pH in your stomach to a more comfortable level.

Bee and wasp stings

Bee stings are acidic - they contain formic acid. Applying a mild base such as bicarbonate of soda (baking soda) paste can help neutralise the acid and reduce pain. Wasp stings, on the other hand, are alkaline. They are best treated with a mild acid such as vinegar. This is a practical application of neutralisation in first aid.

Soil treatment

Many Australian soils are naturally acidic, especially in high-rainfall regions. Crops such as wheat, canola and legumes grow best in slightly acidic to neutral soil (pH 6-7). Farmers add lime (calcium carbonate, a base) or dolomite to acidic soil to raise the pH. This neutralisation reaction improves soil structure, increases nutrient availability, and promotes healthy root growth.

In some parts of Western Australia, soils can be too alkaline for certain crops. Farmers may add sulfur or acidic compost to lower the pH. Managing soil pH through neutralisation is essential for Australian agriculture.

Other applications

• Water treatment: Acids or bases are added to adjust the pH of drinking water and wastewater before release.
• Shampoo formulation: Shampoos are carefully balanced to be slightly acidic, matching the natural pH of hair and skin.
• Battery acid spills: Bases such as sodium bicarbonate are used to safely neutralise acid spills.

In everyday language, "salt" means sodium chloride - the white crystals you sprinkle on food. In chemistry, a salt is any ionic compound formed when an acid reacts with a base. Salts are made of positively charged metal ions and negatively charged non-metal ions held together by strong electrostatic forces.

Common salts and their uses

When you take an antacid containing calcium carbonate, the neutralisation reaction produces calcium chloride (a salt), water and carbon dioxide gas. The salt is not harmful - it simply passes through your digestive system.