Types of chemical reactions - OCR GatewayReactions of acids

Acids take part in reactions in which salts are produced. In these reactions, the hydrogen ions in the acids are replaced by metal ions or ammonium ions.

Reactions with metals

A salt and hydrogen are produced when acids react with metals. In general:

acid + metal → salt + hydrogen

For example:

hydrochloric acid + magnesium → magnesium chloride + hydrogen

2HCl(aq) + Mg(s) → MgCl₂(aq) + H₂(g)

Example

Hydrogen is collected in a test tube during the reaction between magnesium and hydrochloric acid. Describe the laboratory test for hydrogen.

Put a lighted splint near the mouth of the test tube. Hydrogen ignites with a squeaky pop.

Reactions with carbonates

A salt, water and carbon dioxide are produced when acids react with carbonates. In general:

acid + carbonate → salt + water + carbon dioxide

For example:

hydrochloric acid + copper(II) carbonate → copper(II) chloride + water + carbon dioxide

2HCl(aq) + CuCO₃(s) → CuCl₂(aq) + H₂O(g) + CO₂(g)

Example

Carbon dioxide is given off during the reaction between copper carbonate and hydrochloric acid. Describe the laboratory test for carbon dioxide.

Bubble the gas through limewater. Carbon dioxide turns limewater milky or cloudy white.

Predicting the salt formed

The names of salts have two parts:

1. The first part comes from the metal, or the metal in the base or carbonate used. If ammonia or ammonium carbonate is used, the name starts with ‘ammonium’.
2. The second part comes from the acid used:
   • chloride from hydrochloric acid
   • nitrate from nitric acid
   • sulfate from sulfuric acid
   • phosphate from phosphoric acid

For example, copper(II) sulfate is made when copper oxide reacts with sulfuric acid.