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.