Study Guide: Moles, Concentrations and Dilutions

Produced by Graham Currell, University of the West of England, Bristol in association with:
Royal Society of Chemistry, 'Discover Maths for Chemists' website
, and

Essential Mathematics and Statistics for Science, 2nd Edition
   Graham Currell and Antony Dowman, Wiley-Blackwell, 2009

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Why do chemists use both mass (e.g. in grams) and 'numbers of moles' to describe the amount of a material?
It is important to realise that a 'mole' describes a specific number of atoms or molecules (depending on whether it is an element or compound), just as a 'dozen' eggs describes a specific number of eggs. This number is important when combining reagents in a reaction, just as the number of eggs is used as the amount of eggs in a given recipe.
It is also necessary to use mass as this is the method by which amounts of the material are measured on the laboratory scale.
The result is that you have to be happy about converting easily between moles and grams!

Most resource topics listed below include a short self-assessment exercise with video answers. If you need further help in understanding these topics, you may be able to link directly to a suggested resource and/or search the Discover Maths for Chemists website or other resources using the appropriate 'keywords' and 'level'.

Resource topics in order of development
(click to run self-assessment))
Suggested resource Keywords Level
Moles and grams   moles, grams Basic
Concentrations   concentration, molar Basic
Dilutions   dilution Basic
Errors and uncertainties in concentrations and dilutions EURACHEM Guide* propagation of errors Intermediate

* EURACHEM Guide: "Quantifying Uncertainty in Analytical Measurement"

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