Concentration of Solutions (Molarity) Calculations
- Concentration of a solution refers to the amount of solute dissolved in a given solvent.
term description example solute substance that dissolves solid sodium chloride, NaCl(s) solvent substance that enables solute to dissolve liquid water, H2O(l) solution mixture of solute dissolved in solvent sodium chloride dissolved in water, NaCl(aq)
- Concentration of a solution can be given in moles of solute per litre of solution (mol L-1 or mol/L or M).(1)
solute solvent solution units of measurement moles
moles per litre
mol L-1 (mol/L or M)
- Molarity is the term used to describe a concentration given in moles per litre.
- Molarity has the units mol L-1 (or mol/L or M).
- Molarity, concentration in mol/L or mol L-1, is given the symbol c (sometimes M).
For a 0.01 mol L-1 HCl solution we can write :
[HCl] = 0.01 mol L-1 (concentration implied by square brackets around formula)
c(HCl) = 0.01 mol L-1 (c stands for concentration, formula given in round brackets or parentheses)
- Equation (formula or expression) to calculate the molarity of a solution (concentration in mol L-1) is
c = n ÷ V where c = concentration of solution in mol L-1 (mol/L or M),
n = moles of substance being dissolved (moles of solute),
V = volume of solution in litres (L)
- This equation (formula or expression) can be re-arranged to find:
moles of solute given molarity and volume of solution:
n = c × V
volume of solution given moles of solute and molarity:
V = n ÷ c