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Classification of Colloids - Based on Phases

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Question

Write the dispersed phase and dispersion medium of the following colloidal systems:
(i) Smoke
(ii) Milk
What are lyophilic and lyophobic colloids? Which of these sols can be easily coagulated on the addition of small amounts of electrolytes?

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Solution

Dispersed phase Dispersed medium
Smoke Solid Gas
milk Liquid Liquid
Lyophilic colloid:- Lyophilic sols are relatively stable as a strong force of interaction exists between colloidal particles and liquid. Ex. :- Gelatin, starch.

Lyophobic colloid:- lyophobic sols are less stable as a weak force exists between colloidal particles and liquid.
Ex. :- Metal hydroxide, metal sulphides.
lyophobic colloid easily gets coagulated on an addition of a small amount of electrolyte.

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Q. What are lyophilic and lyophobic colloids? Which of these sols can be easily coagulated on addition of small amounts of electrolytes?

Q. Which of the following statements are correct?
1. The smaller the gold number of lyophobic colloid, the larger will be its protective power.
2. Lyophilic sols, in contrast to lyophobic sols are easily coagulated on the addition of small amounts of electrolytes.
3. Ferric chloride solution is used to stop bleeding from a fresh cut because it coagulates the blood.
4. The flocculation value of arsenious sulfide sol is independent of the anion of the coagulating electrolyte.

Q. Lyophilic colloidal sols are much more stable than lyophobic colloidal sols. This is due to the extensive solvation of lyophilic colloidal sols, which form a protective layer outside it which prevents it from forming associated colloids. Lyophilic colloidal sols also protect lyophobic colloidal sols from precipitation by the action of electrolytes. This is due to the formation of a protective layer by the lyophilic sols outside lyophobic sols. Lyophilic sols are also called protective sols.
Gelatin (lyophilic) protects gold sol (lyophobic) from coagulation on the addition of a solution of sodium chloride. The protective powers of different colloidal sols are measured in terms of gold number.
Gold number is defined as the amount of protective sol in milligrams that prevents the coagulation of 10 mL of a given gold sol on adding 1 mL of a

10 %

solution of sodium chloride. Thus, the smaller the gold number of a lyophilic sol, the greater is the protective power.

[A g I] I^{-}

colloidal sol can be coagulated by the addition of a suitable cation. 1 mol

[A g I] I^{-}

A g N O_{3}, P b (N O_{3})_{2}

F e (N O_{3})_{3}

Q. Assertion :Lyophilic sols are reversible sols. Reason: Lyophilic sols can be reconstituted by simply remixing the dispersed phase and dispersion medium.

Q. Colloidal dispersions can be classified based on the nature of interaction as – Lyophilic or Lyophobic. Which of the two is readily obtained by shaking or warming a substance with a suitable solvent or dispersion medium?

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