Concentration of Solutions Calculations (M = n ÷ V) |
Key Concepts
- The concentration of a solution is usually given in moles per litre (mol L-1 OR mol/L).
This is also known as molarity.
- Concentration, or Molarity, is given the symbol M.
A short way to write that the concentration of a solution of hydrochloric acid is 0.01 mol/L is to write [HCl]=0.01M
The square brackets around the substance indicate concentration.
- M = n ÷ V
M = concentration of solution in mol/L,
n = moles of substance,
V = volume of solution in litres (L)
- This formula can be re-arranged:
n = M x V
V = n ÷ M
Examples
1. M = n ÷ V
Calculate the concentration (molarity) of a sodium chloride solution containing 0.125 moles sodium chloride in 0.5 litres of water.
- M = n ÷ V in litres
- n = 0.125mol
- V in litres = 0.5L
- [NaCl(aq)] = M = 0.125 ÷ 0.5 = 0.25M (or 0.25mol/L or 0.25mol L-1)
2. n = M x V
Calculate the moles of copper sulfate in 250mL of 0.02M copper sulfate solution.
- n = M x V
- M = 0.02M
- V = 250mL = 250 ÷ 1000 = 250 x 10-3L = 0.250L (since there are 1000mL in 1L)
- n = 0.02 x 250 x 10-3 = 0.005mol
3. V = n ÷ M
Calculate the volume of a 0.80M potassium bromide solution containing 1.6 moles of potassium bromide.
- V = n ÷ M
- n = 1.6mol
- M = 0.80M
- V = 1.6 ÷ 0.80 = 2.00L
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