NEET Chemistry Surface Chemistry Questions Solved

BOARD

(a) Adsorption of a gas on surface of solid is generally accompained by a

decrease in entropy, still it is a spontaneous process. Explain.

(b) Some substances can act both as colloids and crystalloids. Explain.

(c) What will be the charge on AGI colloidal particles when it is prepared

by adding small amount of ${\mathrm{AgNO}}_{3}$ solution to KI solution in water?

What is responsible for the development of this charge?

We know $∆\mathrm{G}=∆\mathrm{H}-\mathrm{T}∆\mathrm{S}$ for adsorption.  are negative

and $∆\mathrm{H}>\mathrm{T}∆\mathrm{S}$. Thus from this equation $∆\mathrm{G}$ is negative. Therefore,

(b) A crystalloid can be found to behave as a colloid under a different

set of conditions and vice-versa.

Example: NaCl behaves as a crystalloid when dissolved in water but

behaves as a colloid when dissolved in benzene.

(c) When ${\mathrm{AgNO}}_{3}$ solution is added to KI solution, the precipitated AgI

adsorbs I-ions from the dispersion medium and negatively charged

colloidal solution results.

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