Question

What is the use of cotton wool moistened with
lead acetate placed in glass tube of gutzeit
apparatus? (1 marks )
Ans.
To trap carbon dioxide gas
To trap sulphur dioxide gas
To trap hydrogen sulphide gas
To trap arsine gas
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Answer 1

Arsenic's limit test is based on the reaction of arsenic gas with hydrogen ion to form yellow stain on reaction with mercuric chloride paper in the presence of reduction agents such as potassium iodide. It is also called a Gutzeit test and requires special equipment. Arsenic,

which is present in the sample as arsenic acid, is reduced to arsenic acid by reducing agents such as potassium iodide, stan acid, zinc, hydrochloric acid, etc. Hydrogen further reduces arsenic acid to arsine (gas) and reacts to form yellow stain on reacting with mercuric chloride paper. Cotton wool dipped in a solution of lead acetate is used to trap any hydrogen sulfide gas released with arsine gas.