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What products form when acids react with metals, carbonates and bases, and how does neutralisation work?

Describe the characteristic reactions of acids with metals, bases and carbonates, and explain neutralisation in terms of hydrogen and hydroxide ions

A focused answer to the O-Level Combined Science outcome on acid reactions. Acids with metals, bases and carbonates, the salt-plus-water and salt-plus-hydrogen patterns, and neutralisation as the reaction of hydrogen and hydroxide ions.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

SEAB wants you to know the three characteristic reactions of acids (with metals, with bases, and with carbonates), the general products of each, and how neutralisation is explained at the ion level. The reaction patterns are short to learn and appear constantly in structured questions, so you should be able to write a balanced equation and name the salt for any acid.

The answer

Acid plus metal

A reactive metal reacts with a dilute acid to give a salt and hydrogen gas:

acid+metal→salt+hydrogen\text{acid} + \text{metal} \rightarrow \text{salt} + \text{hydrogen}

For example, Zn+2HCl→ZnCl2+H2\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2. Only metals above hydrogen in the reactivity series react this way; copper and silver do not. The hydrogen gives a squeaky pop with a lighted splint.

Acid plus base

An acid reacts with a base (a metal oxide or hydroxide) to give a salt and water only:

acid+base→salt+water\text{acid} + \text{base} \rightarrow \text{salt} + \text{water}

For example, H2SO4+CuO→CuSO4+H2O\text{H}_2\text{SO}_4 + \text{CuO} \rightarrow \text{CuSO}_4 + \text{H}_2\text{O}. This is a neutralisation reaction; no gas is produced.

Acid plus carbonate

An acid reacts with a metal carbonate to give a salt, water and carbon dioxide:

acid+carbonate→salt+water+carbon dioxide\text{acid} + \text{carbonate} \rightarrow \text{salt} + \text{water} + \text{carbon dioxide}

For example, 2HCl+CaCO3→CaCl2+H2O+CO22\text{HCl} + \text{CaCO}_3 \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2. The carbon dioxide turns limewater milky, which is the standard test.

Naming the salt

The salt's name comes from the metal and the acid:

  • hydrochloric acid gives chlorides,
  • sulfuric acid gives sulfates,
  • nitric acid gives nitrates.

So zinc reacting with sulfuric acid gives zinc sulfate.

Neutralisation in terms of ions

The essence of every acid-base neutralisation is the same single reaction:

H++OH−→H2O\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}

Hydrogen ions from the acid combine with hydroxide ions from the alkali to form water. The metal and the acid's negative ion are spectator ions; they stay in solution and become the salt when the water evaporates.

Examples in context

Example 1. Treating indigestion. Antacid tablets contain bases such as magnesium hydroxide or calcium carbonate. They neutralise excess hydrochloric acid in the stomach, turning the painful acid into a harmless salt and water (and carbon dioxide for the carbonate ones), a direct use of acid-base reactions in medicine.

Example 2. Acid rain attacking limestone buildings. Rain made acidic by dissolved sulfur and nitrogen oxides reacts with the calcium carbonate in limestone and marble, producing soluble salts, water and carbon dioxide. Over decades the stone is eaten away, which is why old statues lose their detail, an everyday example of the acid-carbonate reaction.

Try this

Q1. Write a word equation for the reaction between hydrochloric acid and magnesium oxide. [2 marks]

  • Cue. Hydrochloric acid + magnesium oxide gives magnesium chloride + water (acid plus base gives salt plus water).

Q2. Name the gas made when an acid reacts with a carbonate and describe the test for it. [2 marks]

  • Cue. Carbon dioxide; it turns limewater milky (cloudy white).

Q3. Write the ionic equation for neutralisation and explain what the spectator ions do. [2 marks]

  • Cue. H++OH−→H2O\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}; the spectator ions stay in solution and form the salt when the water evaporates.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original4 marksDilute sulfuric acid is added to magnesium ribbon. Name the gas produced and describe a test for it, write the balanced equation for the reaction, and name the salt formed.
Show worked answer →

The gas produced is hydrogen.

Test for hydrogen: a lighted splint placed at the mouth of the tube gives a squeaky pop.

Balanced equation: Mg+H2SO4→MgSO4+H2\text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2.

The salt formed is magnesium sulfate.

Markers reward naming hydrogen, the squeaky-pop test with a lighted splint, the correctly balanced equation, and the salt name magnesium sulfate.

Original3 marksExplain, in terms of ions, what happens during the neutralisation of hydrochloric acid by sodium hydroxide solution, and write the ionic equation for the reaction.
Show worked answer →

In neutralisation, hydrogen ions from the acid react with hydroxide ions from the alkali to form water. This removes the ions responsible for acidity and alkalinity, so the solution moves towards pH 7.

Ionic equation: H++OH−→H2O\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}.

The sodium and chloride ions are spectator ions; they remain in solution and form the salt sodium chloride when the water is evaporated.

Markers reward hydrogen ions reacting with hydroxide ions to form water, the correct ionic equation, and recognising the spectator ions that make the salt.

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