Jawaharlal Nehru Technological University Hyderabad B. Pharmacy I Year PHARMACEUTICAL INORGANIC CHEMISTRY-I Previous Question Paper (October-2020 - R17)

The limit test for arsenic is based on the Gutzeit test, which involves the reduction of arsenic compounds to arsine gas (AsH3) using zinc and hydrochloric acid in the presence of a reducing agent like potassium iodide. The evolved arsine gas reacts with mercuric chloride paper to form a yellow-brown stain.

Procedure: The sample is dissolved in water and placed in a Gutzeit apparatus containing zinc, hydrochloric acid, and potassium iodide. A lead acetate-soaked cotton plug is placed in the tube to trap any hydrogen sulfide gas. The evolved arsine gas passes through a mercuric chloride paper disc fixed at the top of the tube. After 40 minutes, the intensity of the stain produced is compared with a standard stain prepared using a known quantity of arsenic. If the stain from the sample is less intense than the standard, it passes the test.

The limit test for sulphates is based on the precipitation reaction between sulphate ions and barium chloride in the presence of dilute hydrochloric acid. This reaction produces barium sulphate, which remains as a white turbidity in the solution.

Procedure: Two Nessler cylinders are used. In the first cylinder (test), a specific quantity of the substance is dissolved in water, and 1 ml of 5 M hydrochloric acid is added. In the second cylinder (standard), a known volume of 0.1089% w/v potassium sulphate solution is taken, and 1 ml of 5 M hydrochloric acid is added. Both solutions are diluted to 50 ml with distilled water. To both cylinders, 1 ml of barium chloride reagent is added, and the solutions are stirred. After standing for 5 minutes, the turbidity produced in the test cylinder is compared against the standard cylinder. The test passes if the turbidity in the test cylinder is not greater than that of the standard.