Surface Chemistry — Page 2 | JEE Chemistry

Q11

Most suitable salt which can be used for efficient clotting of blood will be :

A Mg(HCO3)2

B NaHCO3

C FeCl3

D FeSO4

Correct Answer

Option C

Solution

According to Hardy-Schulze rule, for negatively charged sol, most (+ve) charged ion is needed for efficient coagulation.

Blood is a negatively charged sol.

Hence FeCl3 can be used for blood clotting and it from Fe3+ ion.

Q12

Which one of the following statements is FALSE for hydrophilic sols?

A They do not require electrolytes for stability.

B The sols cannot be easily coagulated.

C These sols are reversible in nature.

D Their viscosity is of the order of that of H2O.

Correct Answer

Option D

Solution

1.

Viscosity of hydrophilic sol > viscosity of H2O 2.

Hydrophilic sol is more stable so can't be easily coagulated.

3.

Hydrophilic sols are reversible sols.

4.

No electrolytes are required to stabilise hydrophilic sol.

Q13

The nature of charge on resulting colloidal particles when FeCl3 is added to excess of hot water is :

A neutral

B sometimes positive and sometimes negative

C positive

D negative

Correct Answer

Option C

Solution

If FeCl3 is added to excess of hot water, a positively charged sol of hydrated ferric oxide is formed due to adsorption of Fe3+ ions.

Q14

For the coagulation of a negative sol, the species below, that has the highest flocculating power is :

A Na+

B Ba2+

C PO

_4^{3 - }

D SO

_4^{2 - }

Correct Answer

Option B

Solution

For a negative sol, a positive ion is required for flocculation.

The greater the valence of the flocculating ion added, the greater is its power to cause precipitation.

This is called Hardy-Schulz law.

So, Ba+2 has highest flocculating power.

Q15

The charges on the colloidal CdS sol and TiO2 sol are, respectively :

A positive and positive

B positive and negative

C negative and negative

D negative and positive

Correct Answer

Option D

Solution

Oxides & Hydroxide sol are positive so TiO2 is positive sol.

Sulphide sol are negatively charge so CdS is negatively charge sol.

Q16

When silver nitrate solution is added to potassium iodide solution then the sol produced is :

A AgI / I

-

B AgI / Ag+

C KI / NO

_3^ -

D AgNO3 / NO

_3^ -

Correct Answer

Option A

Solution

\mathop {AgN{O_3}(aq.)}\limits_{(drop\,by\,drop)} + \mathop {KI(aq.)}\limits_{excess} \overset{{}}\longrightarrow \mathop {AgI/{I^ - }}\limits_{Sol}

Q17

Match with : Example of colloids Classification

List - I		List - II
(a)	Cheese	(i)	dispersion of liquid in liquid
(b)	Pumice stone	(ii)	dispersion of liquid in gas
(c)	Hair cream	(iii)	dispersion of gas in solid
(d)	Cloud	(iv)	dispersion of liquid in solid Choose the most appropriate answer from the options given below

A (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

B (a)-(iv), (b)-(i), (c)-(iii), (d)-(ii)

C (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)

D (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Correct Answer

Option D

Solution

Cheese $\to$ liquid in solid Pumice stone $\to$ gas in solid Hair cream $\to$ liquid in liquid Cloud $\to$ liquid in gas

Q18

Which one of the following is correct for the adsorption of a gas at a given temperature on a solid surface?

A

\Delta

H > 0,

\Delta

S > 0

B

\Delta

H > 0,

\Delta

S < 0

C

\Delta

H < 0,

\Delta

S < 0

D

\Delta

H < 0,

\Delta

S > 0

Correct Answer

Option C

Solution

(i) Adsorption of gas at metal surface is an exothermic process of

\Delta

H < 0 (ii) As the adsorption of gas on metal surface reduces the free movement of gas molecules thus restricting its randomness hence

\Delta

S < 0

Q19

Tyndall effect is more effectively shown by :

A true solution

B lyophilic colloid

C lyophobic colloid

D suspension

Correct Answer

Option C

Solution

Tyndall effect is observed in lyophobic colloids

Q20

Lyophilic sols are more stable than lyophobic sols because :

A there is a strong electrostatic repulsion between the negatively charged colloidal particles.

B the colloidal particles have positive charge.

C the colloidal particles have no charge.

D the colloidal particles are solvated.

Correct Answer

Option D

Solution

In the lyophilic colloids, the colloidal particles are extensively solvated.