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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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Practice

To calculate the molarity given the moles and volume, enter the moles of substance and the volume in litres, then click the Calculate button. The answer will appear in the textboxes at the bottom.

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