Concentration Calculations – Mass Concentration
Mass concentration is amount of solute (in g) present per dm3 of solution.
For example, if we dissolve 10 g of copper sulfate in a small amount of distilled water
and then make up the volume with distilled water to 1 dm3 (one litre) we have a
solution of copper sulfate with a concentration of 10 g dm-3. The same concentration
could be obtained by dissolving 20 g of copper sulfate in 2 dm3 of water.
In general:
in g
mass concentration 
mass of solute
volume of solution
in dm3
in g dm-3
Example: 25 g of sodium chloride is dissolved in distilled water and the volume is
made up to 200 cm3 with distilled water. What is the mass concentration in g dm-3?
Solution: Remember to convert the volume to dm3. 200 cm3 = 0.200 dm3.
mass of solute
mass concentration 
volume of solution
25 g

0.200 dm 3
 125 g dm -3
Questions:
1. Work out the mass concentration (in g dm-3) in each of these cases:
(a) 15 g of sodium chloride dissolved in 120 cm3 of solution
(b) 200 g of potassium nitrate dissolved in 800 cm3 of solution
(c) 10 g of aluminium sulphate dissolved in 1 litre of solution
2. A bottle of potassium chloride solution purchased from a down-market chemical
company claimed to have a mass concentration of 250 g dm-3. To test this, a 5 cm3
sample was taken and on evaporation of the water 1.036 g of potassium chloride was
obtained. What was the actual mass concentration of the solution?
3. The concentration of sodium chloride in seawater is approximately 35 g dm-3. How
much salt can be obtained by evaporation of 15 litres of seawater?
4. A set of instructions for a chemistry practical (not at SWCHS!) contained the
following instruction: “Dissolve 38 g of iron(II) chloride in 40 ml of water”.
Calculate the mass concentration that would result. Hence, given that the solubility of
iron(II) chloride in water at 20 oC is only 685 g dm-3, determine whether or not this
instruction is possible.