Acids & Bases

Acid rain forms when sulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in atmospheric water to make sulfuric and nitric acid. It damages ecosystems, corrodes buildings, and harms aquatic life.

Acids are substances that produce hydrogen ions (H⁺) in water. They taste sour, react with metals to produce hydrogen gas, react with carbonates to produce carbon dioxide, and have pH values below 7.

Bases are substances that neutralise acids. An alkali is a base that dissolves in water, producing hydroxide ions (OH⁻). Alkalis have a pH above 7 and feel slippery to touch.

Acids and alkalis are all around us — in food, cleaning products, our bodies, and the environment. Knowing the pH of a substance and understanding the hazards of strong acids and alkalis helps us use them safely.

Indicators are substances that change colour depending on whether a solution is acidic or alkaline. They are used in chemistry to identify acidic or alkaline conditions and to find the endpoint of a neutralisation reaction.

Neutralisation is the reaction between an acid and a base (or alkali) to produce a salt and water. The pH of the mixture moves towards 7 (neutral) as the reaction occurs.

The pH scale measures how acidic or alkaline a solution is, running from 0 (most acidic) to 14 (most alkaline), with 7 being neutral. It is based on the concentration of hydrogen ions in the solution.