To Prepare Colloidal Solution of Arsenious Sulphide  , [As2 S3]

Chemistry Lab ManualNCERT Solutions Class 12 Chemistry Sample Papers

Theory
Arsenious sulpide, As2S3 is a lyophobic colloid. It is obtained by the hydrolysis of arsenious oxide (AS203) with boiling distilled water, followed by passing H2S gas through the solution obtained.
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In the colloidal solution of arsenious sulphide, each particle is surrounded by HS- ions, produced by the dissociation of H2S. This sulphide ion layer is further surrounded by the counter ion layer of H+ ions.

Apparatus
Conical flasks (250 ml), beaker (250 ml), round-bottom flask (500 ml), glass-rod, funnel, glass tubing, filter-paper, tripod stand, wire-gauze, iron stand with clamp, burner, etc.

Materials Required
Solid arsenious oxide, H2S gas and distilled water.

Procedure

  1. Clean a conical flask (250 ml) by the use of steaming-out process.
  2.  To this cleaned flask, add 0.2 g of As203 solid and add 100 ml of distilled water.
  3. Boil the solution for about 10 minutes (Fig).
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  4. Filter the above hot solution through flutted filter paper and receive the filtrate in another beaker (Fig).
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  5. Pass a slow current of H2S into As203 solution as shown in Fig.
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    The solution develops a yellow colour due to formation of As2S3. Continue passing H2S till the intensity of colour does not change further.
  6. Expel excess of H2S gas from the sol by boiling the sol till the escaping gas does not turn lead acetate paper black.
  7. Filter the solution through flutted-filter paper and collect the bright yellow filtrate in a dry conical flask and cork it. Label it as “Arsenious Sulphide Sol”.

Precautions

  1. Use cleaned apparatus since As2S3 sol is affected by even traces of impurities.
  2. Handle arsenious oxide with care since it is highly poisonous. Wash your hands immediately every time after handling this chemical. While doing this experiment do not eat or drink anything.