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Classification of Colloids - Based on nature of interaction

Gold number o...

Question

Gold number of lyophilic sol is such property that:

A

the larger its value, the greater is the peptising power

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B

the lower its value, the greater is the peptising power

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C

the lower its value, the grater is the protecting power

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D

the larger its value, the greater is the protecting power.

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Solution

The correct option is B the lower its value, the grater is the protecting power
Gold number of a lyophilic sol is such a property that the lower is its value, the greater is the protecting power.

The gold number is the minimum amount of the protective colloid in milligrams required to just prevent the coagulation of a 10 mL of a given gold sol when 1 mL of a $10 %$ solution of sodium chloride is added to it.

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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.

The coagulation of 100 mL of colloidal solution of gold is completely prevented by the addition of 0.25 g of a substance “

X

” to it before the addition of 1 mL of

10 % N a C l

solution. The gold number of “

X

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. Consider the following statements.
I. The colour of the hydrophobic sol depends on the wavelength of the light scattered by the dispersed particle.
II. The smaller the gold number value of a hydrophilic colloid, the greater is its protective power.
III. The movement of sol particle under an applied electric potential is called electroosmosis.
Which of the above statements are correct?

The protective power of the lyophilic colloids is expressed in terms of gold number a term introduced by Zsigmondy. Gold number is the number of milligrams of the protective colloid which prevent the coagulation of

10

ml of red gold sol. When

1

10

percent solution of sodium chloride is added to it. Thus, smaller the gold number of lyophilic colloid, the greater is the protective power.

On addition of one mL of solution of

10 %

N a C l

10

mL of red gold sol in presence of

0.025

g of starch, the coagulation is just prevented. The gold number of starch is :

Q. The bulk modulus and the density of water are greater than those of air. With this much of information, we can say that velocity of sound in air
(a) is larger than its value in water
(b) is smaller than its value in water
(c) is equal to its value in water
(d) cannot be compared with its value in water.

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