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Concentration - GCSE Chemistry Definition

Reviewed by: Richard Boole

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What is concentration?

In GCSE Chemistry, concentration is the amount of a substance (solute) dissolved in a certain volume of liquid. Depending on your exam board and tier, the units of concentration are grams per cubic decimeter (g / dm3) or moles per cubic decimeter (mol / dm3). 

Exam board

Concentration

(g/dm3)

Concentration

(mol/dm3)

AQA GCSE

All tiers

Higher tier only

Edexcel GCSE

All tiers

Chemistry only

OCR Gateway GCSE

Higher tier only

Higher tier only

WJEC GCSE

Higher tier only

Concentration equation

The equation for concentration in grams per cubic decimeter (g / dm3) is:

concentration space left parenthesis straight g space dm to the power of negative 3 end exponent right parenthesis space equals space fraction numerator mass space of space solute space left parenthesis straight g right parenthesis over denominator volume space of space solution space left parenthesis dm cubed right parenthesis end fraction

The equation for concentration in moles per cubic decimeter (mol / dm3) is:

concentration space left parenthesis mol space dm to the power of negative 3 end exponent right parenthesis space equals space fraction numerator amount space of space solute space left parenthesis mol right parenthesis over denominator volume space of space solution space left parenthesis dm cubed right parenthesis end fraction

Concentration moles formula triangle

One of the most common mistakes in concentration calculations is not using the correct units for volume. Questions often give volume in cm3 but concentration requires dm3, so a conversion must be used:

How to convert from cm3 to dm3 and back

Why is concentration important?

Concentration plays an important role in various chemical reactions, for example:

  • In titrations, chemists measure the concentration of an unknown solution by reacting it with a solution of known concentration.

  • Concentration can be used to control the rate of chemical reactions

    • High concentration means more particles in a given volume, which often leads to faster reaction rates. 

    • Low concentration means less particles in a given volume, which often leads to slower reaction rates. 

  • In industry, concentration calculations can be performed before a chemical reaction is completed. This can potentially reduce the amount of chemicals needed and waste.

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Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

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