Surface Chemistry

JEE Chemistry · 85 questions · Page 5 of 9 · Click an option or "Show Solution" to reveal answer

Q41

For the following Assertion and Reason, the correct option is Assertion : For hydrogenation reactions, the catalytic activity increases from Group 5 to Group 11 metals with maximum activity shown by Group 7-9 elements. Reason : The reactants are most strongly adsorbed on group 7-9 elements.

A Both assertion and reason are true and the reason is the correct explanation for the assertion.

B The assertion is true, but the reason is false.

C Both assertion and reason are true but the reason is not the correct explanation for the assertion.

D Both assertion and reason are false.

Correct Answer

Option B

Solution

Reactants must not get adsorbed so strongly that they are immobilised and other reactants are left with no space on the catalyst’s surface for adsorption.

Q42

Gold numbers of some colloids are : Gelatin : 0.005 - 0.01, Gum Arabic : 0.15 - 0.25; Oleate : 0.04 - 1.0; Starch : 15 - 25. Which among these is a better protective colloid ?

A Gelatin

B Gum Arabic

C Oleate

D Starch

Correct Answer

Option A

Solution

Gold number of a protective colloid is a minimum weight of it in milligrams which must be added to 10 ml of a standard red gold sol. so that no coagulation of the gold sol. (i.e. change of colour from red to blue) takes place when 1 ml of 10% sodium chloride solution is rapidly added to it.

Obviously, smaller the gold number of a protective colloid, the greater is the protective actioin.

It is given that the gelatin has lowest gold number thus, it would serve as a better protective colloid than colloids in the rest of the options.

Q43

Match List I and List II .tg .tg List I List II A. Osmosis I. Solvent molecules pass through semi permeable membrane towards solvent side. B. Reverse osmosis II. Movement of charged colloidal particles under the influence of applied electric potential towards oppositely charged electrodes. C. Electro osmosis III. Solvent molecules pass through semi permeable membrane towards solution side. D. Electrophoresis IV. Dispersion medium moves in an electric field. Choose the correct answer from the options given below :

A A-III, B-I, C-IV, D-II

B A-III, B-I, C-II, D-IV

C A-I, B-III, C-IV, D-II

D A-I, B-III, C-II, D-IV

Correct Answer

Option A

Solution

Correct match is : .tg .tg A.

Osmosis III.

Solvent molecules pass through semi premeable membrane towards solution side.

Reverse osmosis I.

Solvent molecules pass to solvent side through SPM.

Electro osmosis IV.

Dispersion medium moves in an electric field.

Eletrophoresis II.

Movement of colloidal particle towards oppositely charged electrodes.

Q44

Among the following, correct statement is :

A Brownian movement is more pronounced for smaller particles than for bigger–particles

B Sols of metal sulphides are lyophilic.

C Hardy Schulze law states that bigger the size of the ions, the greater is its coagulating power.

D One would expect charcoal to adsorb chlorine more than hydrogen sulphide.

Correct Answer

Option D

Solution

(a) Brownian motion caused by the bombardment of the particles by molecules of the median.

In smaller particle the bombardment is not effective enough so that it can change it's direction and perform zig zag motion.

But for bigger particle zig zag motion happens as bombardment is effective. (b) Inorganic sols are lyophobic.

Metal sulphates are inorganic sols so it is lyophotic. (c) Hardly Schulze does not depends on the size of the ion it depends on the size of the ion it depends on the charge on the ion. (d) Molar mass of Cl2 is 71 and molar mass of H2S is 34 and in both the molecule Nanderwaal force of attraction present.

As Cl2 has more mass than H2S So it's vanderwall force of attraction will be more and tendency to melt will also be more.

So, Cl2 will get easily absorbed.

Q45

Which one of the following is not a property of physical adsorption?

A Higher the pressure, mre the adsorption

B Lower the temperature, more the adsorption

C Greater the surface area, more the adsorption

D Unilayer adsorption ocurs

Correct Answer

Option D

Solution

Physical absorption increases with increase in pressure and decreases with increases in temperature.

When surface are increases then physical absorption also increases.

Physical absorption can perform multiple layer of absorption.

Q46

Match with .tg .tg

List - I		List - II
(A)	Lyophilic colloid	(I)	Liquid-liquid colloid
(B)	Emulsion	(II)	Protective colloid
(C)	Positively charged colloid	(III)	FeCl $_3$ + NaOH
(D)	Negatively charged colloid	(IV)	FeCl $_3$ + hot water

A (A) - (II), (B) - (I), (C) - (IV), (D) - (III)

B (A) - (III), (B) - (I), (C) - (IV), (D) - (II)

C (A) - (II), (B) - (I), (C) - (III), (D) - (IV)

D (A) - (III), (B) - (II), (C) - (I), (D) - (IV)

Correct Answer

Option A

Solution

(A) Protective colloids are lyophilic colloids (B) Emulsions are liquid in liquid colloidal solutions (C) FeCl3 + hot water forms positively charged colloidal solution of hydrated ferric oxide.

(D) FeCl3 + NaOH forms negatively charged colloidal solution due to preferential adsorption of OH- ions

Q47

For a linear plot of log (x/m) versus log p in a Freundlich adsorption isotherm, which of the following statements is correct ? (k and n are constants)

A Both k and 1/n appear in the slope term.

B 1/n appears as the intercept.

C Only 1/n appears as the slope

D log (1/n) appears as the intercept.

Correct Answer

Option C

Solution

According to Freundlich adsorption isotherm

\log {x \over m} = \log K + {1 \over n}\log \,P

Thus if a graph is plotted between log

(x/m)

and log

P,

a straight line will be obtained The slope of the line is equal to

1/n

and the intercept on log

x/m

axis is will correspond to

log

K.

Q48

Amongst the following statements regarding adsorption, those that are valid are (a)

\Delta

H becomes less negative as adsorption proceeds (b) On a given adsorbent, ammonia is adsorbed more than nitrogen gas (c) On adsorption, the residual force acting along the surface of the adsorbent increases (d) With increase in temperature, the equilibrium concentration of adsorbate increases

A (c) and (d)

B (a) and (b)

C (d) and (a)

D (b) and (c)

Correct Answer

Option B

Solution

(a) Since adsorption is exothermic process, as adsorption proceeds number of active sites present over adsorbent decreases, so less heat is evolved. (b) Since NH3 has higher force of attraction on adsorbent due to its polar nature. (c) As the adsorption increases, residual forces over surface decreases. (d) Since process is exothermic, on increasing temperature it shift to backward direction, so concentration of adsorbate particle decreases.

Q49

Which of the following is used for the preparation of colloids?

A Van Arkel Method

B Bredig’s Arc Method

C Mond Process

D Ostwald Process

Correct Answer

Option B

Solution

Bredig's arc method is used for the preparation of colloids.

Q50

The disperse phase in colloidal iron (III) hydroxide and colloidal gold is positively and negatively charged, respectively, which of the following statements is NOT correct?

A magnesium chloride solution coagulates, the gold sol more readily than the iron (III) hydroxide sol.

B sodium sulphate solution causes coagulation in both sols

C mixing the sols has no effect

D coagulation in both sols can be brought about by electrophoresis

Correct Answer

Option C

Solution

When oppositely charged sols are mixed their charges are neutralised.

Both sols may be partially or completely precipitated.

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