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ChemistryGCSE, IGCSE & A Level

What is concentration?

Concentration is the amount of solute dissolved in a given volume of solution, usually in moles per cubic decimetre.

Concentration explained

Volumes are almost always given in cm³ and must be divided by 1000 before use. That single conversion causes more lost marks than any other step in titration questions.
Titration calculations chain three ideas: moles from the standard solution, mole ratio from the equation, and concentration of the unknown.

Key formula

c=nVc = \dfrac{n}{V}

Worked example

0.050.05 mol in 250 cm3250\,\text{cm}^{3} gives c=0.050.25=0.2 mol dm−3c = \frac{0.05}{0.25} = 0.2\,\text{mol dm}^{-3}.

Examiner tip

Use concordant titres only — those within 0.10 cm³ of each other — and state that you have done so when calculating the mean.

Concentration: common questions

How do I convert cm³ to dm³?
Divide by 1000. There are 1000 cm³ in one dm³, which is the same as one litre.
What is the difference between concentration in mol dm⁻³ and g dm⁻³?
Multiply the molar concentration by the molar mass to get g dm⁻³, and divide to go back.

Related terms

Mole

A mole is the amount of substance containing 6.02 × 10²³ particles — the chemist's counting unit that links mass to number of particles.

Titration

A titration is a quantitative technique that finds an unknown concentration by reacting it with a solution of known concentration until the end point.

Molar mass

Molar mass is the mass of one mole of a substance in grams, numerically equal to its relative formula mass.

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