To perform a limit test for sulphate in a given sample of tap water.

 Experiment

Object:

To perform a limit test for sulphate in a given sample of tap water.

Reference:

Parle A., "Pharmaceutical Chemistry 1 Laboratory Manual”, CBS Publishers and Distributors Pvt. Ltd.,Ed 1st, 2008, pp 59

Requirements:

•Chemical required: Hydrochloric acid, Barium sulphate, and Barium chloride

•Apparatus required: Measuring cylinder, glass rod, pipette and Nessler’s cylinder, etc.

Theory:

Limit tests are quantitative or semi-quantitative test designed to identify and control a small number of impurities which are likely to be present in the substance. This test involves the  reaction of Barium chloride with soluble sulphate to form the precipitate of Barium sulphate

which is insoluble in dilute hydrochloric acid. The Barium sulphate precipitate is white in color.

Reaction - 

SO4-- + BaCl2 → BaSO4 + Cl-

(White ppt.)

Na2 SO4 + BaCl2→ BaSO4 + NaCl

(White ppt.)

Procedure:

STANDARD -

 Take 1mL of 0.1089 w/v of Na2SO4 or K2SO4 as per I.P. in Nessler cylinder. Add 2 mL

of dilute Hydrochloric acid. Makeup the volume up to 45 ml with distilled water. Add in this solution of

5 mL of Barium sulphate reagent. Stirrer the solution with a glass rod and allow to stand for 5 minutes.

TEST-

Dissolve the specific quantity of test substances in 10 mL of tap water. Add 2 mL of dilut Hydrochloric acid. Makeup the volume up to 45 ml with distilled water. Add in this solution of 5 mL of Barium sulphate reagent Stirrer the solution with a glass rod and allow to stand for 5minutes.

Observation:

The opalescence of the test solution is less/more than the standard solution. If the opalescence of

the test solution has been less than the standard opalescence, the sample will pass the limit test.

Result:

Limit test for sulphate was performed.