Question

Explain the process of obtaining crystals of sodium sulphate by titration.

Answer 1

Sodium sulphate crystals can be obtained by titrating dilute sulphuric acid (H₂SO₄) with sodium hydroxide (NaOH) solution using a suitable indicator.

1. Take a known volume of dilute sodium hydroxide solution in a conical flask and add a few drops of a suitable indicator.
2. Add dilute sulphuric acid from a burette until the end point is reached.
3. Note the volume of acid required for complete neutralisation.
4. Repeat the titration without adding the indicator, using the same volumes of acid and sodium hydroxide.
5. Transfer the resulting sodium sulphate solution to an evaporating dish and concentrate it by gentle heating.
6. Allow the concentrated solution to cool. Crystals of hydrated sodium sulphate (Na₂SO₄·10H₂O) separate out.
7. Filter the crystals and dry them between sheets of filter paper.

Chemical equation:

\[\ce{2NaOH + H2​SO4 ​→ Na2​SO4​ + 2H2​O}\]