Chemistry

Surface Chemistry

Question:

What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophobic sols easily coagulated?

Answer:

Lyophillic colloids (solvent loving) are those substances that directly pass into the colloidal state when brought- in contact with the solvent, e.g., proteins, starch, rubber, etc.
These sols are quite stable because of the strong attractive forces between the particles of disperse phase and the dispersion medium.
Lyophobic colloids (solvent hating) are those substances that do not form the colloidal sol readily when mixed with the dispersion medium.These sols are less stable than the lyophilic sols. Examples of lyophobic sols include sols of metals and their insoluble compounds like sulphides and hydroxides.
The stability of hydrophobic sol is only due to the presence of charge on the colloidal parties. If charge is removed, e.g., by addition of suitable electrolytes, the particles will come nearer to each other to form aggregate, i.e., they will coagulate and settle down. On the other hand, the stability of hydrophilic sol is due to charge as well as solvation of the colloidal particles. Thuf, for coagulation to occur easily both the mentioned factors have to be removed.

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Surface Chemistry

Q 1.

Why is the ester-hydrolysis slow in the beginning and becomes faster after sometime?

Q 2.

Why is it essential to wash the precipitate with water before estimating it quantitatively?

Q 3.

What happens when dialysis is prolonged?

Q 4.

A colloid is formed by adding FeCl3  in excess of hot water. What will happen if excess sodium chloride is added to this colloid?

Q 5.

Explain what is observed
(i) when a beam of light is passed through a colloidal sol.
(ii) an electrolyte, NaCI is added to hydrated ferric oxide sol.
(iii) electric current is passed through a colloidal sol.

Q 6.

Why is Fe(OH)3colloid positively charged, when prepared by adding FeCl3 to hot water?

Q 7.

Give reason why a finely divided substance is more effective as an adsorbent?

Q 8.

What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophobic sols easily coagulated?

Q 9.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
(a) Both Assertion and Reason are correct and the Reason is the correct explanation for Assertion.
(b) Both Assertion and Reason arc correct but Reason is not the correct explanation for Assertion.
(c) Assertion is correct but Reason is incorrect.
(d) Both Assertion and Reason are incorrect.
(e) Assertion is incorrect but Reason is correct

Assertion (A): An ordinary filter paper impregnated with collodion solution stops the flow of colloidal particles.
Reason (R): Pore size of the filter paper becomes more than size of colloidal particle.

Q 10.

Assertion (A): Colloidal solutions show colligative properties.
Reason (R): Colloidal particles are large in size.

Q 11.

Why does the white precipitate of silver halide become coloured in the presence of dye eosin.

Q 12.

How does a delta form at the meeting place of sea and river water?

Q 13.

How does a solid catalyst enhance the rate of combination of gaseous molecules?

Q 14.

What are the applications of adsorption in chemical analysis?

Q 15.

How do emulsifying agents stabilize the emulsion?

Q 16.

What is the role of adsorption in froth floatation process used especially for concentration of sulphide ores?

Q 17.

Why is chemisorption referred to as activated adsorption?

Q 18.

Assertion (A): Colloidal solutions do not show Brownian motion.
Reason (R): Brownian motion is responsible for stability of sols.

Q 19.

What do you understand by shape selective catalysis? Why are zeolites good shape selective catalysts?

Q 20.

Distinguish between the meaning of the terms adsorption and absorption. Give one example of each.

Q 21.

What are the factors which influence the adsorption of a gas on a solid?

Q 22.

Give four examples of heterogeneous catalysis.

Q 23.

What do you mean by activity and selectivity of catalysts?

Q 24.

What happens when gelatin is mixed with gold sol?

Q 25.

Match the types of colloidal systems given in Column I with the name given in Column II.
ncert-exemplar-problems-class-12-chemistry-surface-chemistry-20

Q 26.

Assertion (A): Detergents with low CMC are more economical to use. Reason (R): Cleansing action of detergents involves the formation of micelles. These are formed when the concentration of detergents becomes equal to CMC.

Q 27.

Freundlich adsorption isotherm is given by the expression  x/m=KP1/n. Which of the following conclusions can be drawn from this expression?
ncert-exemplar-problems-class-12-chemistry-surface-chemistry-15

Q 28.

Why is it important to have clean surface in surface studies?

Q 29.

What is collodion?

Q 30.

Action of soap is due to emulsification and micelle formation. Comment

Q 31.

Which of the following electrolytes will have maximum coagulating value
ncert-exemplar-problems-class-12-chemistry-surface-chemistry-7

Q 32.

H2 gas is adsorbed on activated charcoal to a very little extent in comparison
to easily liquefiable gases due to
(a) very strong van der Waals interaction
(b) very weak van der Waals forces
(c) very low critical temperature
(d) very high critical temperature.

Q 33.

What type of solutions are formed on dissolving different concentrations of soap in water?

Q 34.

Why does leather get hardened after tanning?

Q 35.

How does a delta form at the meeting place of sea and river water?

Q 36.

Method of formation of solution is given in Column I. Match it with the type of solution given in Column II.
ncert-exemplar-problems-class-12-chemistry-surface-chemistry-17

Q 37.

Write any two characteristics of Chemisorption.

Q 38.

What is the role of desorption in the process of catalysis.

Q 39.

What role does adsorption play in heterogeneous catalysis?

Q 40.

Which of the following phenomenon occurs when a chalk stick is dipped in ink?
(a) Adsorption of coloured substance
(b) Adsorption of solvent
(c) Absorption and adsorption both of solvent
(d) Absorption of solvent.

Q 41.

How does the precipitation of colloidal smoke take place in Cottrell precipitator?

Q 42.

What is the role of activated charcoal in gas mask used in coal mines?

Q 43.

Give an example where physisorption changes to chemisorption with rise in temperature. Explain the reason for change.

Q 44.

At the equilibrium position in the process of adsorption
ncert-exemplar-problems-class-12-chemistry-surface-chemistry-1

Q 45.

Which of the following colloids cannot be coagulated easily?
(a) Lyophobic colloids (b) Irreversible colloids
(c) Reversible colloids (d) Lyophilic colloids

Q 46.

What happens when a lyophilic sol is added to a lyophobic sol?
(a) Lyophobic sol is protected.
(b) Lyophilic sol is protected.
(c) Film of lyophilic sol is formed over lyophobic sol.
(d) Film of lyophobic sol is formed over lyophilic sol.

Q 47.

In a reaction, catalyst changes  
(a) physically (b) qualitatively
(c) chemically (d) quantitatively

Q 48.

Which of the following phenomenon occurs when a chalk stick is dipped in ink?
(a) Adsorption of coloured substance
(b) Adsorption of solvent
(c) Absorption and adsorption both of solvent
(d) Absorption of solvent.

Q 49.

What causes Brownian motion in colloidal dispersion?

Q 50.

Why are some medicines more effective in the colloidal form?