Page 1 :
A Practical Book of Pharmaceutical Inorganic Chemistry _Limit Tests, , _ Experiment No. 08, , , , Aim: To perform the limit test of Arsenic for the given sample., Principle:, , The limit test for arsenic is based on the reduction of the arsenic in the arsenious state to, the arsine gas (AsH;) with zinc and hydrochloric acid. The arsine gas stains the mercuric, chloride paper yellow., , The sample is dissolved in acid whereby the arsenic present as impurity in the sample, gets converted to arsenic acid. The arsenic acid is reduced to arsenious acid by reducing, agents like stannous acid, potassium iodine etc. The nascent hydrogen formed during the, reaction further reduce arsenious acid to the arsine gas. The arsine gas reacts with mercuric, , chloride paper to produce a yellow stain., As** —> H3AsOg, (Impurity) (Arsenic acid), H3AsO, + —— > H3AsO3, (Arsenic acid) (Arsenious acid), H3AsO3; +3H,2 —> AsH3 + 3H20, (Arsenious acid) (Arsine gas), 2AsH3 + HgCl, —> Hg(AsH2)2 + 2HCI, (Arsine) (Mercurous chloride) (Yellow stain), The depth of the yellow stain depends upon the amount of arsenic present in the sample,, which is compared with that of standard stain produced from a known amount of arsenic., , The apparatus is as per I.P. 1996:, , , , , , , , , , , , , , “48, ‘lab., il, {, | |, a Vist, afd I, 100 mi, , Fig. 1: Gutzeit apparatus for limit test A for arsenic (Dimensions in millimetres), 15, , Scanned with CamScanner

Page 2 :
ame, , A Practical Book of Pharmaceutical Inorganic Chemistry __, , Limi Te, , Structure and Dimensions:, , Reagent Preparations:, , - Stannous chloride solution AsT: 9, , 1. The apparatus consists of a 100 ml bottle or conical flask closed ee, ground-glass stopper through which passes a glass tube (about 20 cm x 5 mm), , 2. The lower part of the tube is drawn to an internal diameter of 1.0 me and 15 pp,, from its tip is a lateral orifice 2 to 3 mm in diameter. When the tube ls In position, , ’ A lower surface o, the stopper the lateral orifice should be at least 3 mm below the f th, , stopper. / Ri, 3. The upper end of the tube has a perfectly flat surface at right angles to the axis of the, tube., 4. A second glass of the same internal diameter and 30 mm long, with a at Ma, surface, is placed in contact with the first and is held in position by two spiral spring;, or clips P, , 5. Into the lower tube, insert 50 to 60 mg of lead acetate cotton, loosely packed, or 3 L_, small plug of cotton and a rolled piece of lead acetate paper weighing 50 to 60 mg, , 6 Between the flat surfaces of the tubes, place a disc or a small square of mercuric, chloride paper large enough to cover the orifice of the tube (15 mm x 15 mm)., , Preparation of the test solution: - r, , The solution of water soluble substances is prepared with water and _stannated, hydrochloric acid AsT. The solution of substances such as metallic carbonates, which, effervesces with acids, is obtained with brominated hydrochloric acid AsT. The substances, which are insoluble e.g., BaSO,, bentonite or kaolin are diffused in water., , It is prepared by adding stannous chloride solution to an equal volume of hydrochloric, acid AsT, reducing to the original volume by boiling and filtering through a fine-grain, filter paper., , Stannated hydrochloric acid AsT:«, , It is prepared by adding 1 ml of stannous chloride solution AsT to 100 ml of hydrochloric, acid AsT., , Preparation of standard arsenic solution (10 ppm As):, , , , Dissolve 0.330 g of arsenic trioxide in 5 ml of 2 M sodium hydroxide and dilute to, 250.0 ml with water. Dilute 1 volume of this solution to 100 volumes with water., , , , ae, , 16, , Scanned with CamScanner

Page 3 :
A Practical Book of Pharmaceuyost Inorganic Chemistry, , Zinc AsT;, , It us the granulated zinc which compia. with the following additional test. To 10 g of the, , granulated zinc adds 15 mi of the stannous chionde solution AsT and S$ mi of 01 M, potassium iodide Apply the genera! test but allow the reaction to continue for one hour, No visible stain should be produced on the mercuric chionde paper Repeat the test by, adding 0.1 mi of standard arsenic solution (10 ppm As), a faint but distinct yellow stain is, , produced, , Requirements:, (a) Glasswares: Gutzeit’s apparatus, measuring cylinder, conical flask, glass rod, dropper, , etc, , (b) Chemicals: Test solution, stannous chloride solution, stannated hydrochloric acid, 7, standard arsenic solution, granulated zinc, potassium iodide,, , (Hg@Cl,) paper, , , , , , , , , , Procedure:, , Test Standard Reasons, , 1 The test solution which is | 1. 1 mi of arsenic standard | 1 Suspected sample is, , j prepared as Girected in solution (10 ppm As) is taken which might, , | the individual diluted to 50 mi with have an impurity of, , | monograph is introduced water arsenic and make its, , into the bottle or conical solution as per, , | flask monograph, , 12. 5 ml of 1 M potassium | 2. 5 ml of 1 M potassium | 2. (i) Stannous chloride, , | jadide, 5 mi of stannated iodide, 5 ml of stannated is used for, , | hydrochloride solution hydrochloride solution complete evolution, , | AST and 10 g of zinc AsT AsT and 10 g of zinc AsT of arsine gas., , | are added. are added. (ii) Zine, potassium, , iodide and, , stannous chloride, are used as a, reducing agent., , (iii) Hydrochloric acid, is used to make, the solution acidic., , 3, Immediately, the 3. Immediately, the 3. Uniform evolution of, , , , apparatus is assembled, and the flask is immersed, in water bath ata, temperature of 40°C., , , , apparatus is assembled, and the flask is immersed, in water bath at a, , , , temperature of 40°C., , arsine gas is, maintained at 40°C., , , , , , «+. (Contd.), , Limit Tests, , mercuric chloridey, , , , 17, , ‘Scanned with CamScanner

Page 4 :
CN eeE™”™-—lt—“‘_O™O™OS, , A Practical Book of Pharmaceutical Inorganic Chemistry, , Test, , , , Standard, , 4. Arsine gas reacts with, HgClz (paper) ang, make a yellow Stain,, Compare the intensip, of yellow colour in, both., , , , After 40 min. any stain, , produced on the, mercuric chloride (HgCl2), , paper is observed., , 4. After 40 min., any stain 4., produced on the, mercuric chloride (HgCla), Paper is observed., , , , , , , , AsT- Suitable for Arsenic Test (Arsenic free sample), , Note: The stain produced on paper fades on keeping and the, compared immediately. Arsine gas produced is passed throug, purify and trap other impurities like H2S gas., , refore the stains should, h lead acetate solution |, , Conclusion:, After 40 minutes, if the intensity of the yellow stain produced in the standard is mo;, , than that in the test, the sample complies with the limit test of lead., , AA &, , ‘Scanned with CamScanner