Chrominfo: Identification test for bentonite

Learn the identification test for bentonite through a laboratory experiment or practical.

Aim:

To perform identification test for bentonite.

Reference: Indian Pharmacopoeia (IP)

Requirements:

Glasswares and miscellaneous:

Test tube, measuring cylinder, pipette, glass rod, volumetric flask, beaker, funnel, dropper, rubber stopper, test tube stand, test tube holder, balance, etc.

Chemicals:

Bentonite, anhydrous sodium carbonate (Na₂CO₃), ammonium chloride (NH4Cl), sodium hydroxide (NaOH, hydrochloric acid (HCl), thioacetamide (C2H5NS), quinalizarin (C14H8O6), etc.

Theory:

Identification tests are used to determine the drug's quality so that it can be used safely. This identification of bentonite is usually based on the reactions of ions and cations present in the sample, by which we can determine the quality of the drug. Bentonite is a suspension agent made up of colloidal hydrated aluminum silicate.

Bentonite is an odorless powder that's pale buff or cream in color and has a slightly earthy taste. It is water-insoluble, however, when water is added, it expands to around twelve times its original volume. It is insoluble in organic solvents and does not swell upon contact with them.

Procedure:

Fuse 02.00 gm of anhydrous sodium carbonate and 01.00 gm of the sample, then warm the residue with 10.00 ml distilled water. Filter the residue, wash it with 05.00 ml of water, and combine the filtrate and washings. Do the test for the presence of aluminum in the residue and silica in the filtration.

Identification tests for barium ion:

Perform the following tests by dissolving the residue in 10.00 ml of weak hydrochloric acid. Add 0.5 ml of thiocetamide reagent to 02.00 ml of the above-prepared solution. No precipitate is formed. Add 2N solution of sodium hydroxide in a dropwise manner. A gelatinous white precipitate of aluminum hydroxide (Al(OH)3) is found.

In the 02.00 ml of the above solution add 2-4 drops of freshly made 0.05 percent w/v quinlizarin in a 1 percent w/v NaOH solution. Boil, cool, then acidify with an excess of acetic acid, you get a reddish violet color.