Concentration of a Solution

  1. The concentration of a solution tells you how much solute is dissolved in 1 unit volume of solution.
  2. The volume of a solution is measured in dm³ (litres).  1 dm³ = 1000 cm³.
  3. The amount of solute can be measured in grams or moles.
  4. 2 units of concentration used in chemistry are g dm-3 and mol dm-3

Concentration in g dm-3

  1. Concentration is the number of moles of solute per liter of solution.
  2. A concentration of 10 g dm-3 means there is 10 g of solute dissolved in1 dm3 of solution.
Concentration = Mass of solute(g) Volume of solution(dm 3 )
Example 1:
Calculate the concentration of the solution if 28g of NaOH is dissolve in 250cm3 of water.

Answer:
Mass of solute = 28g
Volume of solvent = 250cm³ = 0.25dm³

Concentration= Mass Volume  = 28g 0.25d m 3 =112g/d m 3

Concentration in mol dm-3 (Molarity)

  1. Molarity is probably the most commonly used unit of concentration. It is the number of moles of solute per liter of solution.
  2. A concentration of 2 mol dm-3 means there are 2 moles of solute dissolved in 1 dm3 of solution.
Molarity = Mole of solute(mol) Volume of solution(dm 3 )
Example:
What is the molarity of a solution made when water is added to 0.2 mol of CaCl2 to make 100 cm³ of solution? [RAM: Ca = 40; Cl = 35.5]

Answer:
Number of mole of solute = 0.2 mol
Volume of solvent = 100 cm³ = 0.1 dm³

Molarity =  Number of Mole Volume = 0.2mol 0.1d m 3 =2mol/d m 3


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