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Concentration and dilution explained

Syllabus HAVO: Quantities and relationships

Distinguish added water from final volume and use c₁V₁ = c₂V₂.

The solute remains

Dilution adds solvent. If no solute is lost or reacts, the amount of solute remains constant. A larger volume gives a lower concentration.

Make up to the final volume

Making 25.0 mL up to 250.0 mL is a tenfold dilution. This does not mean adding 250.0 mL of water. Use the same unit for both volumes.

Worked example

25.0 mL of a 0.200 mol/L solution is made up to 250.0 mL.

  1. n = 0.200 × 0.0250 = 0.00500 mol.
  2. c₂ = 0.00500 / 0.2500.

c₂ = 0.0200 mol/L.

Explore the model
EXPLORE THE MODELn₁ = n₂

What happens when you dilute further?

Start: 25 mL of 0.200 mol/L. Change only the final volume.

Concentration0.02 mol/LAmount of solute0.005 mol

The 12 dots are model symbols, not a literal molecular count. Their number stays constant; the numerical values define the calculation.