GCSE Chemistry (AQA)

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Concentration of Solutions (mol/dm3)

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Quantitative chemistry Using concentrations of solutions in mol/dm3

Concentration of Solutions (mol/dm3)

9:22 Calculating Concentration Using Moles and Volume
Spec 4.3.4
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  • Concentration can be measured in grams per decimeter cubed or moles per decimeter cubed.
  • Concentration is a measure of how much solute is present per decimeter cubed of a solution.
  • Calculation for concentration in moles per decimeter cubed: amount of solute in moles divided by the volume in decimeters cubed.
  • Example: 2 moles of solute in 0.5 decimeters cubed solvent results in a concentration of 4 moles per decimeter cubed.
  • Volume should be converted to decimeters cubed before calculating concentrations.
  • If concentration in moles per decimeter cubed is known, the amount of solute in moles can be calculated by rearranging the equation.
  • Example with hydrochloric acid: 0.5 moles per decimeter cubed concentration and 0.1 decimeters cubed volume results in 0.05 moles of solute.
  • The amount of solute in moles can be used to calculate the mass of solute in grams using the equation M = N x Mr.
  • Example: Hydrochloric acid has a relative formula mass of 36.5, resulting in 0.00137 grams of solute.
  • Concentration can be converted between grams per decimeter cubed and moles per decimeter cubed using the relative formula mass.
  • Example calculation: Mass of sodium hydroxide in 50.0 cm�� of a 0.125 mole per decimeter cubed solution.
  • Steps: Recall the concentration equation, rearrange for the amount of solute, convert volume to decimeters cubed, substitute values, calculate mass using M = N x Mr.
  • Concentration is affected by the volume of solvent and the amount of solute.
  • Increasing solvent volume decreases concentration; increasing solute amount increases concentration.

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