Surface Chemistry — Page 7 | JEE Chemistry

Q61

Adsorption of a gas on a surface follows Freundlich adsorption isotherm. Plot of log

{x \over m}

versus log p gives a straight line with slope equal to 0.5, then: (

{x \over m}

is the mass of the gas adsorbed per gram of adsorbent)

A Adsorption is independent of pressure.

B Adsorption is proportional to the pressure.

C Adsorption is proportional to the square root of pressure.

D Adsorption is proportional to the square of pressure.

Correct Answer

Option C

Solution

According to Freundlich adsorption isotherm, in the median range of pressure

{x \over m} \propto {P^{{1 \over n}}}

$\Rightarrow$

{x \over m}

= kP

^{{1 \over n}}

taking log both sides, we get, log

{x \over m}

= logk +

{1 \over n}

logP Here in graph between log

{x \over m}

and logP, slope is

{1 \over n}

and intercepts = log k. Given that, slope = 0.5

\therefore\,\,\,

{1 \over n}

= 0.5 $\Rightarrow$ n = 2

\therefore\,\,\,

{x \over m}

= kP

^{{1 \over 2}}

= k

\sqrt P

$\therefore$ Adsorption is proportional to the square root of pressure.

Q62

3 g of activated charcoal was added to 50 mL of acetic acid solution (0.06N) in a flask. After an hour it was filtered and the strength of the filtrate was found to be 0.042 N. The amount of acetic acid adsorbed (per gram of charcoal) is:

A 36 mg

B 42 mg

C 54 mg

D 18 mg

Correct Answer

Option D

Solution

Let the weight of acetic acid initially be

{w_1}

in

50

ml

of

0.060

N

solution. Let the

N = {{{w_1} \times 1000} \over {M.wt. \times 50}}\,\,\,

(Normality

=0.06

N

)

0.06 = {{{w_1} \times 1000} \over {60 \times 50}}

\Rightarrow \,\,\,\,\,{w_1} = {{0.06 \times 60 \times 50} \over {1000}}

= 0.18\,g = 180\,mg.

After an hour, the strength of acetic acid

=0.042

N

so, let the weight of acetic acid be

{w_2}

N = {{{w_2} \times 1000} \over {60 \times 50}};0.042 = {{{w_2} \times 1000} \over {3000}}

\Rightarrow \,\,\,\,\,\,\,\,\,\,{w_2} = 0.126g = 126mg

So amount of acetic acid adsorbed per

3g

= 180 - 126\,mg = 54\,mg

Amount of acetic acid adsorbed per

g

= {{54} \over 3} = 18\,mg

Q63

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R Assertion A: Amongst

\mathrm{He}, \mathrm{Ne}, \mathrm{Ar}

and

\mathrm{Kr}

; 1

\mathrm{g}

of activated charcoal adsorbs more of

\mathrm{Kr}

. Reason R: The critical volume

\mathrm{V}_{\mathrm{c}}\left(\mathrm{cm}^{3} \mathrm{~mol}^{-1}\right)

and critical pressure

\mathrm{P}_{\mathrm{c}}

(atm) is highest for Krypton but the compressibility factor at critical point

\mathrm{Z}_{\mathrm{c}}

is lowest for Krypton. In the light of the above statements, choose the correct answer from the options given below

A Both A and R are true and R is the correct explanation of A

B A is false but R is true

C Both A and R are true but R is NOT the correct explanation of A

D A is true but R is false

Correct Answer

Option D

Solution

MW order, $\mathrm{Kr}>\mathrm{Ar}>\mathrm{Ne}>\mathrm{He}$ $Z$ (at critical point) $=\dfrac{3}{8}$

Q64

The coagulating power of electrolytes having ions Na+, Al3+ and Ba2+ for arsenic sulphide sol increases in the order:

A Na+ < Ba2+ < Al3+

B Al3+ < Ba2+ < Na+

C Ba2+ < Na+ < Al3+

D Al3+ < Na+ < Ba2+

Correct Answer

Option A

Solution

According to Hardly Schulze rule, greater the charge or cation, greater is its coagulating power for negatively charged solution.

Hence the correct order of coagulating power :

N{a^ + } < B{a^{2 + }} < A{l^{3 + }}

Q65

For coagulation of arsenious sulphate sol, which one of the following salt solution will be most effective ?

A BaCl2

B AlCl3

C NaCl

D Na3PO4

Correct Answer

Option B

Solution

Sulphide is $-$ ve charged colloid.

As coagulation is directly proportional to the effective charge, so cation with maximum charge will be most effective for coagulation.

Al3+ > Ba2+ > Na+ coagulating power.

Q66

Among the colloids cheese (C), milk (M), and smoke (S), the correct combination of the dispersed phase and dispersion medium, respectively is :

A C : liquid in solid ; M : liquid in liquid ; S : solid in gas

B C : liquid in solid ; M : liquid in solid ; S : solid in gas

C C : solid in liquid ; M : liquid in liquid ; S : gas in solid

D C : solid in liqid ; M : solid in liquid ; S : solid in gas

Correct Answer

Option A

Solution

Cheese (C) is liquid dispersed in solid. Milk (M) is liquid dispersed in liquid. Smoke (S) is solid dispersed in gas.

Q67

The Tyndall effect is observed only when following conditions are satisfied: (a) The diameter of the dispersed particles is much smaller than the wavelength of the light used. (b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used. (c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude. (d) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.

A (b) and (d)

B (a) and (c)

C (b) and (c)

D (a) and (d)

Correct Answer

Option A

Solution

Tyndall effect is observed only when (i) The diameter of the dispersed particle is not much smaller than the wavelength of the light used. (ii) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.

So, (b) and (d) are correct.

Q68

A gas undergoes physical adsorption on a surface and follows the given Freundlich adsorption isotherm equation

{x \over m} = k{p^{0.5}}

Adsorption of the gas increase with :

A Decrease in p and increase in T

B Increase in p and decrease in T

C Decrease in p and decrease in T

D Increase in p and increase in T

Correct Answer

Option B

Solution

Physical adsorption increases with increase of pressure and decrease of temperature.

Q69

The correct option among the following is :

A Addition of alum to water makes it unfit for drinking.

B Colloidal medicines are more effective because they have small surface area.

C Colloidal paraticles in lyophobic sols can be precipitated by electrophoresis.

D Brownian motion in colloidal solution is faster if the viscosity of the solution is very high.

Correct Answer

Option C

Solution

Electrophoresis is used to coagulate lyophobic colloids.

Q70

The sol given below with negatively charged colloidal particles is :

A FeCl3 added to hot water

B KI added to AgNO3 solution

C AgNO3 added to KI solution

D Al2O3.xH2O in water

Correct Answer

Option C

Solution

When AgNO3 is added to KI, Iodide ion gets adsorbed on the surface of AgI.

This will result in formation of negatively charged colloids.

When KI is added to AgNO3 following reaction takes place.

Silver cation gets adsorbed on surface of AgI, resulting in formation of positively charged colloids.