Acid Reactions & Salts
Describe and write word equations for the reactions of acids with metals, alkalis (neutralisation), and metal oxides/hydroxides, identifying the salt produced in each case
What a learner can do afterwards
- Writes word equations for: acid + metal → salt + hydrogen; acid + alkali → salt + water; acid + metal oxide → salt + water
- Names the salt formed from a given acid and base (e.g. hydrochloric acid + sodium hydroxide → sodium chloride)
- Describes the test for hydrogen gas (squeaky pop)
- Explains what neutralisation means and gives a practical example (indigestion tablets, treating acidic soil)
1 · Read
You already know what acids and alkalis are, and that a chemical reaction makes new substances. Acids react with three everyday groups of substances: metals, alkalis, and metal oxides. Each time, one of the new substances is a salt. A salt is a compound made from a metal joined to a part that comes from the acid. The salt on your food, sodium chloride, is one you already know. Chemists write these reactions as word equations, where an arrow means 'turns into'.
Drop a piece of magnesium ribbon into hydrochloric acid and it fizzes: hydrochloric acid + magnesium → magnesium chloride + hydrogen. The bubbles are hydrogen gas. To prove it, hold a lit splint near the gas and listen. Hydrogen burns with a squeaky pop, so a pop tells you hydrogen is there. That splint test belongs to hydrogen alone: limewater turning cloudy is the test for carbon dioxide, a different gas.
When an acid reacts with an alkali, the two cancel each other out. This is called neutralisation, and it always makes a salt and water: acid + alkali → salt + water. Neutralisation explains why an indigestion tablet calms an acidic stomach: the tablet holds an alkali that reacts with the extra acid. Gardeners use the same idea when they add lime, another alkali, to acidic soil. Metal oxides react with acids in just the same way: acid + metal oxide → salt + water. Hydrogen only forms when an acid meets a plain metal, so a metal oxide never makes it.
A salt's name has two parts: the metal first, then a part named after the acid. Hydrochloric acid gives 'chloride' salts, sulfuric acid gives 'sulfate' salts, and nitric acid gives 'nitrate' salts. The metal comes from the other reactant, such as the alkali. So when sulfuric acid reacts with sodium hydroxide, the salt that forms is sodium sulfate: sulfuric acid + sodium hydroxide → sodium sulfate + water.
Acids make salts in three ways. With a metal you get salt + hydrogen: test the gas with a lit splint and listen for a squeaky pop. With an alkali or a metal oxide you get salt + water, and the alkali reaction is called neutralisation. Name the salt from the metal first, then the acid: chloride, sulfate, or nitrate.
Adapted from OpenStax Chemistry (CC-BY 4.0), openstax.org · license
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