Surface Chemistry — Page 9 | NEET Chemistry

Q81

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.

Q82

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.

Q83

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.

Q84

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

A

{V_C \over V_S } \simeq 1

B

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

C

{V_C \over V_S } \simeq 10^3

D

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

Correct Answer

Option C

Solution

Particle size of colloidal particle

= 1\,m\mu \,\,

to

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}

Q85

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.

Q86

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 .

Q87

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.

Q88

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.

Q89

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.

Q90

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.