Surface Chemistry

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Question
CBSEENCH12011387

A plot of log x/m versus log p for the adsorption of a gas on a solid gives a straight line with slope equal to:

  • -log k

  • n

  • 1/n

  •  log k

Solution

C.

1/n

The empirical relation x/m = kp1/n put forward by Freundlich is known as Freundlich adsorption isotherm. Taking logarithm
log space straight x over straight m space equals space log space straight k space plus 1 over straight n space log space straight p
If the following curve is plotted

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Question
CBSEENCH12011043

Fog is a colloidal solution of 

  • Gas in liquid

  • Solid in gas

  • Gas in gas

  • Liquid in gas

Solution

D.

Liquid in gas

Fog is a colloidal solution of liquid in a gas in which liquid is the dispersed phase whereas gas is the dispersion medium.

Question
CBSEENCH12011157

The ease of adsorption of the hydrated alkali metal ions on an ion exchange resins follows the order

  • Li+ > K+ >Na+> Rb+

  • Rb+ < K+ < Na+ < Li+

  • K+ >Na+>  Rb+ > Li+

  • Na+ < Li+ < K+ < Rb+

Solution

B.

Rb+ < K+ < Na+ < Li+

Ease of adsorption of the hydrated alkali metal ions on an ion-exchange resin decreases as the size of alkali metal ion increases.
since, the order of the size of alkali metal ions
Li+ < Na+ < K+ < Rb+

Thus,  the ease of adsorption follows the order
Rb+ < K+ < Na+ < Li+

Question
CBSEENCH12011362

The Langmuir adsorption isotherm is deduced using  the assumption: 

  • the adsorption takes place in multilayers

  • The adsorption sites are equivalent in their ability to adsorb the particles

  • The adsorbed molecules interact with each other

  • The adsorbed molecules interact with each other

Solution

A.

the adsorption takes place in multilayers

The main points  of Langmuir theroy of adsorption are as:
i) Adsorption takes place on the surface of the solid only till the whole of the surface is completely covered with a unimolecular layer of the adsorbed gas.
ii) Adsorption consist fo two opposing processes (a) condensation, and (b) evaporation.
iii) The rate of condensation depend upon  the uncovered surface of the adsorbent available for condensation.

Question
CBSEENCH12011160

The protecting power of lyophilic colloidal sol is expressed in terms of 

  • Coagulation value

  • Gold number

  • Critical micelle concentration

  • Oxidation number

Solution

B.

Gold number

Lyophobic sols are unstable, so they re-stabilised by adding some lyophilic colloids which protect them from precipitation. Thus, lyophilic colloids are called protecting colloids. Their protecting power is expressed in terms of gold number.
[Lesser the gold number, higher si the protecting power,]