Question

Which of the following are negative colloids?
a.) $Fe{\left( {OH} \right)_3} sol$
b.) $A{s_2}{S_3} sol$
c.) Blood
d.) Gold sol

Answer 1

Hint: To solve this question, we will use the concept of colloids. The colloids are mixtures in which one substance is divided into minute particles. These particles cannot be seen with the naked eyes. We will use these properties of the colloid and see what is negative colloid and positive colloid to solve this question.

Complete step by step solution: Depending upon the charge on the colloidal sol they are classified as positive and negative sols.
The positive charge sols are haemoglobin, metallic hydroxides , sols of basic dyes such as methylene blue etc.
The negative sols are Metal sols e.g. Au, Ag, Cu, etc. metal sulphides, starch, sols of acid dyes, blood etc
In the above example, the negative sols are blood, gold sol and $A{s_2}{S_3} sol$
Hence, the correct option is B, C and D.

Additional Information - The colloidal particle has a certain type of electric charge as one of the major features of colloidal solutions. All colloidal particles carry the same type of charge with a particular colloidal solution, while the dispersion medium has the same but opposite charge. The charge for colloidal particles is therefore balanced by the dispersion medium and the entire colloidal solution is electrically neutral. The colloidal ferric hydroxide parts, for example, are positively charged in a ferric solar hydroxide, whereas the dispersion medium carries the same negative charge.

Note: In order to solve these types of questions, you need to have the concept of solution, colloidal sol and the difference between them. Colloidal sol has very minute particles that cannot be seen with naked eye while can be seen with a microscope. Also the stability of the colloidal solution depends upon the charge on it and as we know the same charges repel each other therefore the colloidal particles do not combine in the colloidal solution.