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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.
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