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SingaporeChemistrySyllabus dot point

What are the typical reactions of acids with metals, bases and carbonates, and how do we recognise the products?

Describe the reactions of acids with metals, with bases and metal oxides, and with carbonates, and write the equations and identify the gases produced

A focused answer to the N(A) Chemistry outcome on the reactions of acids. Acid plus metal, acid plus base or metal oxide, and acid plus carbonate, the salt and gas formed each time, and the tests for the gases.

Generated by Claude Opus 4.88 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

The syllabus wants you to describe the three typical reactions of acids, with metals, with bases and metal oxides, and with carbonates, to write the equations, and to name and test the gases produced. These reactions are the routes used to make salts in the next dot point, so knowing the products by heart is essential. The pattern is simple: every acid reaction makes a salt plus something else.

The answer

Acid plus metal

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

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

For example, magnesium with hydrochloric acid gives magnesium chloride and hydrogen. You see fizzing, and the gas gives a squeaky pop with a lighted splint. Only metals above hydrogen in the reactivity series react this way.

Acid plus base or metal oxide

An acid reacts with a base (including a metal oxide or metal hydroxide) to give a salt and water only. This is neutralisation:

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

For example, copper(II) oxide with sulfuric acid gives copper(II) sulfate and water. There is no gas. The metal oxide usually dissolves and the solution may change colour.

Acid plus carbonate

An acid reacts with a 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, calcium carbonate with hydrochloric acid gives calcium chloride, water, and carbon dioxide. You see fizzing, and the gas turns limewater milky.

Naming the salt

The salt's name comes from the acid used:

  • hydrochloric acid gives a chloride,
  • sulfuric acid gives a sulfate,
  • nitric acid gives a nitrate.

The first part of the salt name comes from the metal.

Examples in context

Example 1. Fizzing antacids and indigestion. Many indigestion remedies contain a carbonate. When swallowed, the carbonate reacts with the acid in the stomach to form a salt, water, and carbon dioxide, which is why some antacids fizz. The reaction reduces the acidity and eases discomfort.

Example 2. Acid rain attacking statues. Rain that is slightly acidic reacts with the calcium carbonate in limestone and marble statues, producing a soluble salt, water, and carbon dioxide. Over many years the stone is slowly worn away, a real-world example of the acid plus carbonate reaction.

Try this

Q1. Complete the word equation: sulfuric acid + magnesium oxide →\rightarrow ? + ?. [2 marks]

  • Cue. Magnesium sulfate + water (acid plus metal oxide gives a salt and water, no gas).

Q2. Name the gas produced when zinc reacts with hydrochloric acid, and describe how you would test for it. [2 marks]

  • Cue. Hydrogen; hold a lighted splint to the gas and it burns with a squeaky pop.

Q3. Write the word equation for nitric acid reacting with sodium carbonate. [2 marks]

  • Cue. Nitric acid + sodium carbonate →\rightarrow sodium nitrate + water + carbon dioxide.

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.

Original5 marksMagnesium is added to dilute hydrochloric acid. (a) Name the gas produced and describe the test for it. (b) Name the salt formed. (c) Write the balanced symbol equation with state symbols.
Show worked answer →

(a) The gas is hydrogen. Test it with a lighted splint: hydrogen burns with a squeaky pop.

(b) The salt formed is magnesium chloride.

(c) The balanced equation is:

Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)\text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)

What markers reward: hydrogen confirmed by the squeaky pop, the salt magnesium chloride, and the correctly balanced equation with state symbols.

Original4 marksDilute hydrochloric acid is added to calcium carbonate chips. (a) Name the gas given off and describe its test. (b) State two things you would observe during the reaction.
Show worked answer →

(a) The gas is carbon dioxide. Bubble it through limewater: the limewater turns milky (a white precipitate forms).

(b) Observations: bubbles or fizzing are seen as the gas is given off, and the calcium carbonate chips get smaller and eventually disappear as they react.

What markers reward: carbon dioxide confirmed by milky limewater, and two clear observations such as fizzing and the solid dissolving or getting smaller.

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