Surface Chemistry — Page 4 | NEET Chemistry

Q31

If x gram of gas is adsorbed by m gram of adsorbent at pressure P, the plot of log

{x \over m}

versus log P is linear. The slope of the plot is : (n and k are constants and n > 1)

A 2 k

B log k

C n

D

{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}}

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.

Q32

'Adsorption' principle is used for which of the following purification method?

A Chromatography

B Sublimation

C Distillation

D Extraction

Correct Answer

Option A

Solution

Principle used in chromotography is adsorption.

Q33

Gold numbers of protective colloids A, B, C and D are 0.50, 0.01, 0.10 and 0.005, respectively. The correct order of their protective powers is

A D < A < C < B

B C < B < D < A

C A < C < B < D

D B < D < A < C

Correct Answer

Option C

Solution

For a protective colloid $\mu$ lesser the value of gold number better is the protective power.

Thus the correct order of protective power of

A,B,C

and

D

is $\Rightarrow$

\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,

\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,

\left( A \right)\,\, < \,\,\left( C \right)\,\, < \,\,\left( B \right)\,\, < \,\,\left( D \right)

Gold number

\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0.50\,\,\,\,\,\,0.10\,\,\,\,\,\,0.01\,\,\,\,\,\,0.005

Hence

(c)

is the correct answer

Q34

Which of the following is not an example of heterogenous catalytic reaction?

A Ostwald's process

B Combustion of coal

C Hydrogenation of vegetable oils

D Haber's process

Correct Answer

Option B

Solution

Then is no catalyst is required for combustion of coal.

Q35

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.

Q36

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.

Q37

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.

Q38

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.

Q39

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

Q40

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