The mole is the unit for amount of substance. The number of particles in a substance can be found using the Avogadro constant. The mass of product depends upon the mass of limiting reactant.

The amount in moles of a solute in a given volume of solution can be calculated if the concentration of the solution is known. The mass of solute can then be calculated.

Rearranging the equation for concentration below:

Gives:

Amount of solute in mol = concentration in mol/dm^{3} × volume in dm^{3}

Calculate the amount of sodium hydroxide, NaOH, in 25.0 cm^{3} of solution of concentration 0.1 mol/dm^{3}.

Converting the volume from cm^{3} to dm^{3}, 25.0 cm^{3} = 25.0 ÷ 1000 = 0.025 dm^{3}.

Amount of NaOH in mol = concentration in mol/dm^{3} × volume in dm^{3}

= 0.1 mol/dm^{3} × 0.025 dm^{3}

= 0.0025 mol

If the amount in mol of a solute in a given volume of solution is known, its mass can also be calculated.

- Question
For the example above, calculate the mass of NaOH in 25.0 cm

^{3}of solution. (*M*_{r}= 40 g)Mass = amount × relative formula mass

= 0.0025 × 40

= 0.1 g

If the volumes of two solutions that react completely are known, and the concentration of one of the solutions is known, then the concentration of the other solution can be calculated.

25.0 cm^{3} of hydrochloric acid, HCl, of concentration 1.0 mol/dm^{3} reacts with 20.0 cm^{3} of sodium hydroxide, NaOH, solution. Calculate the concentration of the NaOH solution. The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H_{2}O(l)

Converting volumes from cm^{3} to dm^{3}:

- volume of HCl = 25.0 cm
^{3}= 25.0 ÷ 1000 = 0.025 dm^{3} - volume of NaOH = 20.0 cm
^{3}= 20.0 ÷ 1000 = 0.020 dm^{3}

Substituting into the equation to find the amount of HCl in the given volume:

Amount of HCl in mol = concentration in mol/dm^{3} × volume in dm^{3}

= 1.0 mol/dm^{3} × 0.025 dm^{3}

= 0.025 mol

The equation shows that 1 mol of HCl reacts with 1 mol of NaOH. So the amount of NaOH in 20.0 cm^{3} is 0.025 mol.

Substituting into the equation to find the concentration of NaOH:

= 1.25 mol/dm^{3}