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Molar Concentration (Oxford AQA IGCSE Chemistry): Revision Note

Philippa Platt

Written by: Philippa Platt

Reviewed by: Stewart Hird

Updated on

Oxford AQA ChemistryOxford AQA Combined Science Double Award: Chemistry

Solution Calculations

What is concentration?

  • Concentration refers to the amount of solute there is in a specific volume of the solvent

  • It can be expressed in moles per decimetre cubed and calculated using the following equation

concentration (mol / dm3)space equals space fraction numerator number space of space moles 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

  • 1 decimetre cubed (dm3) is the same as 1 litre

    • 1 decimetre cubed (dm3) = 1000 cm3

  • Some students find formula triangles help them to understand the relationship:

Diagram to show the relationship between moles, concentration and volume

Concentration moles formula triangle, downloadable IB Chemistry revision notes
The concentration-moles formula triangle can help you solve these problems

  • You may be given data in a question which needs to be converted from cm3 to dm3 or the other way around

Conversion of cm3 and dm3

unit-conversion

To go from cm3 to dm3 divide by 1000. To go from dm3 to cm3 multiply by 1000

Worked Example

Calculate the amount of solute, in moles, present in 2.5 dm3 of a solution whose concentration is 0.2 mol/dm3.

Answer:

Step 1: Write down the information you are given in the question:

  • Concentration of solution: 0.2 mol/dm3

  • Volume of solution: 2.5 dm3 

Step 2: Calculate the number of moles

  • Moles = concentration x volume

  • Moles = 0.2 x 2.5 = 0.5 mol

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    Author
    Reviewer
    Philippa Platt

    Author: Philippa Platt

    Expertise: Chemistry

    Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener

    Stewart Hird

    Author: Stewart Hird

    Expertise: Chemistry Lead

    Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.