PRACTICAL-INORGANIC CHEMISTRY-LIMIT TEST OF SULPHATE

Object – To perform the limit test for Sulphate as per I.P..

Reference – Sharma N. etal, Practical Inorganic Pharmaceutical Chemistry & Viva voce, Birla publications Pvt. Ltd., Delhi, I Edition, 2007-08, 96.

Materials required –

Chemicals – Barium sulphate reagent, dilute hydrochloric acid, Sodium Chloride, Potassium sulphate, Distill water

Glasswares & Apparatus – Nessler cylinder, Measuring cylinder, Pipette, Glass rod, Spatula, Weighing balance

Theory – Limit tests are quantitative or semi quantitative tests designed to identify and control small quantities of impurity which are likely to be present in the substance. The limit tests for sulphates is based on the reaction between sulphate and barium chloride in presence of hydrochloric acid.

Reaction involved-

BaCl2 + So42-  →  BaSO4 + 2Cl

Hydrochloric acid prevents precipitation of other acid radicals with barium chloride, and in presence of hydrochloric acid only sulphate get precipitated. The turbidity produced in each nessler cylinder was compared transversely. If the turbidity from the sample is less than the standard turbidity, the sample will pass the limit test and vice versa.

Fig : Nessler cylinder

Procedure –

Test solution –

  1. First of all, cleaned and dried Nessler cylinder was taken.
  2. In the Nessler cylinder, 2 gram of sample (NaCl) was taken.
  3. Then, 2 ml of dilute hydrochloric acid was added to it.
  4. Now, 45 ml with water was added.
  5. Then, 5 ml of Barium sulphate reagent was added.
  6. It was stirred well.
  7. Finally it was kept aside for 5 minutes and then turbidity or opalescence was observed.

Standard solution –

  1. First of all, cleaned and dried Nessler cylinder was taken.
  2. In the Nessler cylinder, 1 ml of 0.01089% w/v solution of potassium sulphate and 9 ml of distill water was taken.
  3. Then, 2 ml of dilute hydrochloric acid was added to it.
  4. Now, 45 ml with water was added to it.
  5. Then, 5 ml of barium sulphate reagent was added.
  6. It was stirred well.
  7. Finally it was kept aside for 5 minutes and then turbidity or opalescence was observed.

Inference –

  1. Turbidity of test solution > turbidity of standard solution – test failed
  2. Turbidity of test solution < turbidity of standard solution – test passed
  3. Turbidity of test solution = turbidity of standard solution – test passed

Result – On comparing the turbidity / Opalescence of test solution and standard solution, it was found that the turbidity of test solution is…………………………….. (more than/ less tan / equal to) the standard solution. Hence the sample ……………………………..(passed / failed) the limit test for sulphate.

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