Question

Explain the methods of preparation of colloids of 

1. AS₂S₃

2. S.

Answer 1

1. Double decomposition: 

When hydrogen suiphide gas is passed through a solution of arsenic oxide, a yellow coloured arsenic sulphide is obtained as a colloidal solution.

AS₂O₃  + H₂S → AS₂S₃ + 3H₂O

2. Decomposition: 

When few drops of an acid is added to a dilute solution of sodium thio sulphate, the insoluble free sulphur produced by the decomposition of sodium thiosuiphate accumulates into clusters which impart various colours blue, yellow and even red to the system depending on their growth within the size of colloidal dimensions.