What mistakes do students make with Concentration of solutions?

Claiming that adding more solvent increases concentration. Put it right by explaining that adding solvent increases volume and therefore decreases concentration for the same mass of solute. Treating mass and volume as interchangeable or ignoring one of them. Put it right by relating concentration to both the mass of solute and the volume of solution together. Saying concentration is proportional to volume rather than inversely proportional. Put it right by noting that doubling the volume halves the concentration when the mass is unchanged.

What are the exam tips for Concentration of solutions in Combined Science AQA GCSE?

Use the words directly proportional and inversely proportional explicitly, since Higher Tier explanation questions reward precise relationship language. Support your explanation with a simple numerical example, as this demonstrates understanding rather than repeating the definition.

AQA · GCSE · Combined Science

Course version: 8464 · Version from Sept 2018

(HT only) explain how the mass of a solute and the volume of a solution is…

Full specification wording

Concentration of solutions: (HT only) explain how the mass of a solute and the volume of a solution is related to the concentration of the solution.

Concentration measures how much solute is dissolved in a given volume of solution, linking mass and volume through concentration = mass ÷ volume.

Checked against the AQA 8464 specification (opens in a new tab) on 20 September 2026.

Point 3 of 3
2 key terms

Study notes

From the checked teaching notes for this specification point.

The idea

What earns the marks

State that concentration is directly proportional to the mass of solute when the volume of solution is kept constant.
State that concentration is inversely proportional to the volume of solution when the mass of solute is kept constant.
Express the relationship as concentration = mass of solute ÷ volume of solution and use it to justify the proportionalities.
Apply the relationship to a numerical or practical example, such as showing that dissolving 20 g in 2 dm³ gives 10 g/dm³ whereas the same 20 g in 1 dm³ gives 20 g/dm³.

Common mistakes and how to put them right

Claiming that adding more solvent increases concentration.
Put it right by explaining that adding solvent increases volume and therefore decreases concentration for the same mass of solute.
Treating mass and volume as interchangeable or ignoring one of them.
Put it right by relating concentration to both the mass of solute and the volume of solution together.
Saying concentration is proportional to volume rather than inversely proportional.
Put it right by noting that doubling the volume halves the concentration when the mass is unchanged.

Exam tips

Use the words directly proportional and inversely proportional explicitly, since Higher Tier explanation questions reward precise relationship language.
Support your explanation with a simple numerical example, as this demonstrates understanding rather than repeating the definition.

Try the lesson

The start of the Concentration of solutions: (HT only) explain how the mass of a solute and the volume of a solution is related to the concentration of the solution. lesson, made from checked teaching notes for this specification point.

Have a go first

How does the concentration of a solution change if the volume of the solution is doubled while the mass of the dissolved solute remains the same?

Tip: press 1 to 4 to choose

Listen

Concentration measures how much solute is dissolved in a given volume of solution, linking mass and volume through concentration = mass ÷ volume. For a fixed volume, increasing the mass of solute raises the concentration proportionally: doubling the mass doubles the concentration. For a fixed mass of solute, increasing the volume lowers the concentration: dissolving the same mass in twice the volume halves the concentration. This explains why a small volume of a concentrated solution can contain the same solute mass as a larger volume of a dilute solution. Expressing the relationship as an equation allows predictions about how concentration changes when variables are altered. A strong answer earns marks for these points. State that concentration is directly proportional to the mass of solute when the volume of solution is kept constant. State that concentration is inversely proportional to the volume of solution when the mass of solute is kept constant. Express the relationship as concentration = mass of solute ÷ volume of solution and use it to justify the proportionalities. Apply the relationship to a numerical or practical example, such as showing that dissolving 20 g in 2 dm³ gives 10 g/dm³ whereas the same 20 g in 1 dm³ gives 20 g/dm³. A common slip: Claiming that adding more solvent increases concentration. Instead, explaining that adding solvent increases volume and therefore decreases concentration for the same mass of solute. Exam tip: Use the words directly proportional and inversely proportional explicitly, since Higher Tier explanation questions reward precise relationship language.

See it

A flowchart starting from a single box reading 'Concentration = mass of solute ÷ volume of solution'. This splits into two branches. The first branch is 'Mass of solute kept constant', which leads to two boxes: 'Increasing volume lowers concentration' and 'Concentration inversely proportional to volume'. The second branch is 'Volume of solution kept constant', which leads to two boxes: 'Increasing mass of solute raises concentration' and 'Concentration directly proportional to mass of solute'. — It shows how concentration depends on the mass of solute and the volume of solution, and the direct and inverse proportionalities when one is kept constant.

Key words

Say what each word means before you turn the card.

Concentration of solutions

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Mass, volume and concentration relationships

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See every definition

Concentration of solutions: Measures how much solute is dissolved in a given volume of solution, linking mass and volume through concentration = mass ÷ volume.
Mass, volume and concentration relationships: Expressed as concentration = mass of solute ÷ volume of solution, and used to justify the proportionalities and predict how concentration changes when variables are altered.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 3 boxes numbered instead of named. A flowchart starting from a single box reading 'Concentration = mass of solute ÷ volume of solution'. This splits into two branches. The first branch is 'Mass of solute kept constant', which leads to two boxes: 'Increasing volume lowers concentration' and 'Concentration inversely proportional to volume'. The second branch is 'Volume of solution kept constant', which leads to two boxes: 'Increasing mass of solute raises concentration' and 'Concentration directly proportional to mass of solute'.

1Box 1
2Box 2
3Box 3

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