Preparation of Lyophobic Sol - Arsenious Sulphide Sol

In this article, we have discussed step-by-step procedure to perform an experiment to prepare Arsenious Sulphide sol. Carefully read the content on this page to understand the aim, procedure and the materials required to perform the experiment. Try to perform the experiment and match your result with this.


The aim of this experiment – to prepare Arsenious Sulphide sol.


As2S3 (Arsenious sulphide) is a lyophobic colloid. It is formed due to the hydrolysis of As2O3 (Arsenious oxide) in boiled distilled water. Further H2S gas is passed through the solution. The reaction is as follows:

As2O3 + 3H2O → 2As(OH)3

2As(OH)3 + 3H2S → As2S3 + 6H2O

The particles in Arsenious sulphide colloidal solution are surrounded by HS ions which are formed due to the dissociation of H2S. Sulphide ion layer is surrounded by H+ ions.

Materials required:

The apparatus and materials required for this experiment are as follows:

  1. Beaker 250 mL
  2. Round bottom flask 500 mL
  3. Glass tubing
  4. Conical flask of 250 mL volume
  5. Filter paper
  6. Funnel
  7. Glass rod
  8. Wire gauze
  9. Burner
  10. Tripod stand
  11. Iron stand with clamp
  12. Distilled water
  13. H2S gas
  14. Solid arsenious oxide

Experimental setup:

Steaming out process to clean conical flask


  1. Take a 250 mL of conical flask and clean it by steaming out process.
  2. Add 0.2 g of solid arsenious oxide and 100 mL of distilled water.
  3. Boil the solution for 10 minutes.
  4. With the help of a filter paper, separate the hot solution.
  5. Pass H2S through As2O3 using Kipp’s apparatus as shown in the below figure.

Preparation of As2S3 solution

  1. The colour of the solution changes to yellow which is the result of formation of As2S3.
  2. Expel hydrogen sulphide gas from sol by slowly heating.
  3. Label the filtrate as ‘arsenious sulphide sol’.

Precautions to be taken during the experiment:

  • Use clean apparatus for the experiment as As2S3 gets affected if any even traces of impurities are present.
  • As2S3 is highly poisonous so handle it carefully.

Viva Voce:

1. How to prepare arsenious oxide solution?

Ans: Mix 0.2 g of arsenious oxide in 100 mL of distilled water.

2. Why is it important to clean the apparatus used to prepare As2S3 sol by steaming out process?

Ans: Arsenious Sulphide sol gets affected due to the presence of ionic impurities. Therefore, the apparatus is steam cleaned before the experiment.

3. Boil the mixture of Arsenious oxide solution and distilled for _______ minutes.

Ans: 10 minutes.

4. The particles in Arsenious sulphide colloidal solution are surrounded by ________.

Ans: HS ions.

5. The colour of the solution changes to _______.

Ans: Yellow colour.

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