GCSE Combined Science (AQA)

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Concentration of Solutions (g/dm3)

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Quantitative chemistry Use of amount of substance in relation to masses of pure substances

Concentration of Solutions (g/dm3)

8:24 Calculating Concentration Using Mass and Volume
Spec 4.3.2.5
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  • Chemical reactions often occur in solutions.
  • A solution is made by mixing a solvent (e.g., water) with a solute (e.g., table salt, sodium chloride).
  • When mixed, the solute dissolves in the solvent, forming a solution.
  • A solution with water as the solvent is called an aqueous solution.
  • Concentration of a solution refers to how crowded particles are in a given volume of solvent.
  • Greater number of particles in a given volume means greater concentration.
  • Example: Two solutions with the same volume but different solute amounts have different concentrations.
  • Concentration can be measured in mass per given volume of solution.
  • Concentration equation: Concentration (g/dm��) = Mass of solute (g) / Volume of solution (dm��).
  • Example calculation: A solution with 10 grams of solute in 0.2 dm�� has a concentration of 50 g/dm��.
  • Volume conversion: 1 cm�� = 1 ml = 0.001 dm��.
  • To convert cm�� or ml to dm��, divide by 1000; to convert dm�� to cm�� or ml, multiply by 1000.
  • Mass of solute can be calculated if concentration and volume are known using: Mass = Concentration �� Volume.
  • Example: A solution with a concentration of 20 g/dm�� and volume of 2 dm�� contains 40 grams of solute.
  • Worked example: Calculate mass of magnesium hydroxide in a solution with given concentration and volume.
  • Steps for calculation: Recall equation, rearrange for mass, substitute values, complete calculation, and add units.
  • Example result: 4.0 grams of magnesium hydroxide in the solution.

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