Modified Limit Test for Sulfate (Gravimetric Analysis)

• The modified limit test for sulfate is based on gravimetric analysis, where sulfate ions (SO₄²⁻) are precipitated as barium sulfate (BaSO₄) using barium chloride (BaCl₂).

• The precipitate is then collected, dried, and weighed to determine the sulfate concentration.

Chemical Reaction

Ba²⁺ (aq) + SO₄²⁻ (aq) → BaSO₄ (s)

Procedure of Gravimetric Analysis

1) Prepare Test Solution

• Prepare a solution from the sample, ensuring the sulfate ions are in a soluble form.

2) Add Barium Chloride (BaCl₂)

• Add an excess of BaCl₂ solution to the test solution to precipitate sulfate ions as barium sulfate (BaSO₄).

3) Filter the Precipitate

• Filter the precipitate using a pre-weighed filter paper or crucible, then thoroughly wash the precipitate to remove any impurities.

4) Dry the Precipitate

• Dry the filter paper or crucible containing the precipitate in an oven or desiccator until a constant weight is achieved.

5) Weigh the Precipitate

• Weigh the filter paper or crucible with the dried precipitate.

• Subtract the initial weight of the filter paper or crucible to determine the weight of the barium sulfate (BaSO₄) precipitate.

6) Calculate Sulfate Ion Concentration

• Calculate the sulfate ion concentration in the sample based on the weight of BaSO₄ and the stoichiometry of the reaction.