Surface Chemistry

JEE Chemistry · 85 questions · Page 8 of 9 · Click an option or "Show Solution" to reveal answer

Q71

The volume of a colloidal particle, VC as compared to the volume of a solute particle in a true solution VS, could be

{V_C \over V_S } \simeq 1

{V_C \over V_S } \simeq 10^{-3}

{V_C \over V_S } \simeq 10^3

{V_C \over V_S } \simeq 10^{23}

Correct Answer

Option C

Solution

Particle size of colloidal particle

= 1\,m\mu \,\,

100\,m\mu

(suppose

10\,m\mu

)

{V_C} = {4 \over 3}\pi {r^3} = {4 \over 3}\pi {\left( {10} \right)^3}

Particle size of true solution particle

= 1\,m\mu

Vs = {4 \over 3}\pi {\left( 1 \right)^3}

hence now

{{Vc} \over {Vs}} = {10^3}

Q72

Among the following the false statement is -

A Lyophilic sol can be coagulated by adding an electrote

B Tyndall effect can be used to distinguish between a colloidal solution and a true solution

C It is possible to cause artificial rain by throwing electrified sand carrying charge opposite to the one on clouds from an aeroplane

D Latex is a colloidal solution of rubber particles which are positively charged

Correct Answer

Option D

Solution

Latex is a colloidal solution of rubber particles which are negatively charged.

Q73

Which of the following statements is incorrect regarding physisorptions ?

A It occurs because of vander Waal’s forces.

B More easily liquefiable gases are adsorbed readily.

C Under high pressure it results into multi molecular layer on adsorbent surface.

D Enthalpy of adsorption (

\Delta H_{adsorption}

) is low and positive

Correct Answer

Option D

Solution

In adsorption when two molecule comes closer then bond is created between the molecules and we know when bond is created between molecules the energy gets released so, Adsorption is an exothermic process, hence

\Delta H

will always be negative .

Q74

The adsorbent used in adsorption chromatography is/are - A. silica gel B. alumina C. quick lime D. magnesia Choose the most appropriate answer from the options given below :

A C and D only

B A only

C B only

D A and B only

Correct Answer

Option D

Solution

Commonly used adsorbents in adsorption chromatography are silica gel and alumina.

Q75

The INCORRECT statements below regarding colloidal solutions is :

A The flocculating power of Al3+ is more than that of Na+.

B A colloidal solutions shows Brownian motion of colloidal particles.

C An ordinary filter paper can stop the flow of colloidal particles.

D A colloidal solutions shows colligative properties.

Correct Answer

Option C

Solution

Colloidal solutions can pass through ordinary filter paper but cannot pass through a special filter colloidal solution coated paper.

Q76

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Finest gold is red in colour, as the size of the particles increases, it appears purple then blue and finally gold. Reason R : The colour of the colloidal solution depends on the wavelength of light scattered by the dispersed particles. In the light of the above statements, choose the most appropriate answer from the options given below.

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

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

C A is true but R is false.

D A is false but R is true.

Correct Answer

Option A

Solution

Finest gold sol is red in colour; as the size of particles increases, it appears purple, then blue and finally golden.

The colour of colloidal solution depends on the wavelength of light scattered by the dispersed particles.

The wavelength of light further depends on size and nature of the particles.

Hence, Both A and R are true and R is the correct explanation of A.

Q77

Among the following, the INCORRECT statement about colloids is :

A The range of diameters of colloidal particles is between 1 and to 1000 nm

B they are larger than small molecules and have high molar mass

C They can scatter light

D The osmotic pressure of a colloidal solution is of higher order than the true solution at the same concentration.

Correct Answer

Option D

Solution

Osmotic pressure of colloidal solution is lower than true solution of same concentration.

Q78

The conditions given below are in the context of observing Tyndall effect in colloidal solutions : (A) The diameter of the colloidal particles is comparable to the wavelength of light used. (B) The diameter of the colloidal particles is much smaller than the wavelength of light used. (C) The diameter of the colloidal particles is much larger than the wavelength of light used. (D) The refractive indices of the dispersed phase and the dispersion medium are comparable. (E) The dispersed phase has a very different refractive index from the dispersion medium. Choose the most appropriate conditions from the options given below :

A (A) and (E) only

B (C) and (D) only

C (A) and (D) only

D (B) and (E) only

Correct Answer

Option A

Solution

The phenomenon of scattering of light by colloidal particles as a result of which the path of the beam becomes visible is called a tyndall effect.

Smaller the diameter and similar the magnitude of refractive indices, lesser is the scattering and hence the tyndall effect and viced-versa.

The diameter of the dispersed phase particle should not be smaller than the wavelength of light used because they won't be able to scatter the light so, therefore, the diameter of the dispersed particles should be equal or not much smaller than the wavelength of the light used.

The refractive indies (i.e. the ratio of the velocity of light in vacuum to the velocity of light in any medium) of the dispersed phase and the dispersion medium should differ greatly in magnitude than only the particles will be able to scatter the light and tyndall effect will be obersved.

On the other hand, if the refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude, then there will be no-scattering of light and hence, therefore, no Tyndall effect effect is observed.

Hence answer (A) and (E) are correct.

Q79

Which one of the following characteristics is not correct for physical adsorption?

A Adsorption increases with increase in temperature

B Adsorption is spontaneous

C Both enthalpy and entropy of adsorption are negative

D Adsorption on solids is reversible

Correct Answer

Option A

Solution

As adsorption is an exothermic process.

$\therefore$ Rise in temperature will decrease adsorption (according to Le-chatelier principle).

Q80

In Freundlich adsorption isotherm at moderate pressure, the extent of adsorption

\left( {{x \over m}} \right)

is directly proportional to Px. The value of x is :

\infty

B zero

C 1

{{1 \over n}}

Correct Answer

Option D

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}}

Hence, x =

{{1 \over n}}

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