Concentration · Year 10

In Year 10 you learn: concentration in g/dm³.

The concentration of a solution tells you how much solute is dissolved in each dm³ (litre) of it. In g/dm³ it is the mass in each dm³; in mol/dm³ it is the number of moles. Multiply by the Mᵣ to go from mol/dm³ to g/dm³. Adding water dilutes a solution: the moles stay the same in a bigger volume.

Key facts

  • 1 dm³ = 1 litre = 1000 cm³: divide a volume in cm³ by 1000 to get dm³.
  • concentration (g/dm³) = mass (g) ÷ volume (dm³).

Worked examples

Example 1

20 g of sodium chloride is dissolved in water to make 2 dm³ of solution. What is the concentration in g/dm³?

Answer: 10 g/dm³

Example 2

5 g of copper sulfate is dissolved to make 250 cm³ of solution. Find the concentration in g/dm³.

Answer: 20 g/dm³

Example 3

What mass of sugar is dissolved in 500 cm³ of a sugar solution with a concentration of 40 g/dm³?

Answer: 20 g

Example 4

Which is more concentrated: 6 g of salt in 200 cm³ of solution, or 10 g of salt in 500 cm³ of solution?

Answer: 6 g in 200 cm³ (30 g/dm³, compared with 20 g/dm³)

Other years