Preparation of Lyophobic Sol - Arsenious Sulphide Sol

In this article, we have discussed a 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 materials required to perform the experiment. Try to perform the experiment and match your result with this.

Aim:

The aim of this experiment is to prepare arsenious sulphide sol.

Theory:

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. The 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:

Procedure:

1. Take a 250 mL conical flask and clean it by the 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 filter paper, separate the hot solution.
5. Pass H₂S through As₂O₃ using Kipp’s apparatus as shown in the below figure.

1. The colour of the solution changes to yellow which is the result of the 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 a clean apparatus for the experiment as As₂S₃ gets affected if any 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 distil 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.