Let’s say that a scientist carries out a titration. The titrant in the burette is 1M HCl and the analyte in the conical flask is 50cm³ of sodium hydroxide of an unknown concentration. The scientist wants to determine the concentration of the sodium hydroxide solution. The titration is carried out and it is determined that 27cm³ of hydrochloric acid are required to neutralise the solution.

Step 1: What reaction is occurring here?

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

So the hydrochloric acid and the sodium hydroxide are reacting together in a 1:1 ratio (5 moles of HCl will react with 5 moles of NaOH).

Step 2: How many moles of the titrant were used?

Concentration(mol/dm³) = moles/volume(dm³), so moles = concentration(mol/dm³) x volume(dm³).

The volume of HCl was given in cm³; it needs to be in dm³.

27cm³/1000 = 0.027dm³.

Moles = 1mol/dm³ x 0.027dm³ = 0.027.

0.027 moles of HCl was used to neutralise the NaOH. Because of step 1, this means that the analyte also contained 0.027 moles of NaOH.

Step 3: What’s the concentration of the analyte?

Moles of NaOH: 0.027.

Volume of NaOH (from the start): 50cm³/1000 = 0.05dm³.

Concentration(mol/dm³) = moles/volume(dm³)

Concentration = 0.027 moles/0.05dm³ = 0.54mol/dm³.

The concentration of the sodium hydroxide solution is 0.54mol/dm³ (or 0.54M).