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Concentration Calculations

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Work out the concentration of a solution in g/dm³ and mol/dm³, convert between them, and find the mass you need to make a solution. Watch out for volumes given in cm³.

The rules
  1. concentration (g/dm³) = mass (g) ÷ volume (dm³). Rearrange to get mass = concentration × volume.
  2. Volumes must be in dm³. 1 dm³ = 1000 cm³, so divide cm³ by 1000 to get dm³. Multiply dm³ by 1000 to get cm³.
  3. concentration (mol/dm³) = moles ÷ volume (dm³). Rearrange to get moles = concentration × volume.
  4. moles = mass ÷ Mr, so g/dm³ ÷ Mr = mol/dm³ and mol/dm³ × Mr = g/dm³.
  5. Mr = the sum of the Ar values of every atom in the formula.
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Worked solution

    Relative atomic masses are the AQA values: H 1, C 12, N 14, O 16, Na 23, Mg 24, S 32, Cl 35.5, K 39, Cu 63.5, Zn 65, Ag 108. Concentration in g/dm³ is for all students. Concentration in mol/dm³ is AQA GCSE Chemistry (separate science), Higher tier only.

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