Conversion of Concentration Unit

  1. The chart above shows how to convert the units of concentration from g dm-3 to mol dm-3 and vice versa.
  2. The molar mass of the solute is equal to the relative molecular mass of the solute.


Example 1:
The concentration of a Potassium chloride solution is 14.9 g dm-3. What is the molarity ( mol dm-3) of the solution? [ Relative Atomic Mass: Cl = 35.5; K = 39 ]

Answer:
Relative Formula Mass of Potassium Chloride (KCl)
= 39 + 35.5 = 74.5

Molar Mass of Potassium Chloride = 74.5 g/mol

Molarity of Potassium Chloride
Molarity =  Concentration Molar Mass = 14.9gd m 3 74.5gmo l 1 =0.2mol/d m 3

Example 2
A solution of barium hydrokxide have molarity 0.1 mol dm-3. What is the concentration of the solution in g dm-3? [Relative Atomic Mass: Ba = 137; O = 16; H = 1 ]

Answer:
Relative Formula Mass of barium hydrokxide, Ba(OH)2
= 137 + 2(16+1) = 171

Molar Mass of Potassium Chloride = 171 g/mol
Concentration = Molarity×Molar Mass =0.1mol/d m 3 ×171gmo l 1 =17.1gmo l 1


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