In this question paper, some of the important one mark, two and five marks questions from the chapter Surface Chemistry are covered. The questions are prepared from the book back and previous year questions.
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Questions:

1 Marks

4 x 1 = 4

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

If we add equimolar amount of \(Fe{ \left( OH \right) }_{ 3 }\) to \({ As }_{ 2 }{ S }_{ 3 }\) sol, what will happen?

On passing \({ H }_{ 2 }S\) gas through dilute \({ HNO }_{ 3 }\), the colourless solution becomes turbid. Why?

Define the term 'Tyndall effect'.

Generic 2

6 x 2 = 12

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

What is demulsification? Name two demulsifiers.

Why is the ester hydrolysis slow in the beginning and becomes faster after some time?

The action of enzyme is highly specific. Do you agree with this statement? Explain.

Explain the following:
(a) Emulsification
(b) Emulsifying agent
(c) Demulsifier.

10.

Describe a chemical method each for the preparation of the sols of sulphur and platinum in water.

Generic 3

5 x 3 = 15

11.

How do the size of particles of adsorbent, pressure of gas and prevailing temperature influence the extent of adsorption of a gas on a solid?

12.

Give a reason for the following:
(i) Rough surface of catalyst is more effective than smooth surface.
(ii) Smoke is passed through charged plates before allowing it to come out of chimneys in factories.
(iii) Ne gets easily adsorbed over charcoal than He.

13.

Name the characteristics of enzyme catalysis.

14.

Why are medicines more effective in colloidal state?

15.

(a) Which will adsorb more gas, a lump of charcoal or its powder and why?
(b) Describe the preparation of the following colloidal solutions. Name the method used in each case:
(i) Silver sol
(ii) Sulphur sol

Multiple Choice Question

5 x 1 = 5

16.

According to Freundlich adsorption isotherm, which of the following is correct ?

(a)

\(\frac { x }{ m } \alpha { p }^{ o }\)

(b)

\(\frac { x }{ m } \alpha { p }^{ 1 }\)

(c)

\(\frac { x }{ m } \alpha { p }^{ 1/n }\)

(d)

All the above are correct for different ranges of pressure

17.

The function of gum arabic in the preparation of Indian ink is

(a)

Coagulation

(b)

Peptization

(c)

Protective action

(d)

Adsorption.

18.

Purple of cassius is a cooloidal sol of

(a)

silver

(b)

platinum

(c)

gold

(d)

iron

19.

Which one of the following forms an intrinsic colloid?

(a)

Sulphur

(b)

As₂S₃

(c)

Fe(OH)₃

(d)

Egg albumin

20.

Which of the following is true in respect of adsorption?

(a)

\(\triangle G<0,\triangle S>0,\triangle H<0\)

(b)

\(\triangle G<0,\triangle S<0,\triangle H<0\)

(c)

\(\triangle G>0,\triangle S>0,\triangle H<0\)

(d)

\(\triangle G<0,\triangle S<0,\triangle H>0\)

Fill up / 1 Marks

5 x 1 = 5

21.

Converting a freshly precipitated substance into colloidal state by shaking with a suitable electrolyte is called........................ .

22.

The soze of the colloidal particles lies in the range.....................nm.

23.

A plot of mass adsorbed per gram of the adsorbent versus temperature at constant pressure is called....................... .

24.

If solvent is adsorbed from a solution on the adsorbent, it is called.................adsorption.

25.

Silica gel placed in water vapour results in..........................wher as calcium chloride placed in water vapour results in...................... .

Generic 5

2 x 5 = 10

26.

Radha and Meera are fast friends. They both study in class XII.Radha is a student of science while Meera follows commerce stream. One day, when they were playing, Radha got hurt and started bleeding. Meera took her to house and applied some alum on the cut. The bleeding stopped immediately.
(i)Why bleeding stopped when some alum is applied on the cut?
(ii) What are the values associated with Meera's decision to take Radha to her house and apply alum on her cut?

27.

In an adsorption experiment, a graph between log (x/m) versus log P was found to be linear with a slope of 45^o. The intercept on the log (x/m) axis was found to be 0.310. Calculate the amount of the gas adsorbed per gram of charcoal under a pressure of 0.5 atmosphere.

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Answers Key:

1 Marks

4 x 1 = 4

()
Charged smoke particles get attracted towards oppositely charged plate and get coagulated.

()
Mutual coagulation will take place because \(Fe{ \left( OH \right) }_{ 3 }\) is positively charged colloid, whereas \({ As }_{ 2 }{ S }_{ 3 }\) is negatively charged colloid.

()
It is due to the formation of colloidal sulphur.
H₂S +[O] \(\underrightarrow { dil.H{ NO }_{ 3 } } \) H₂O +S

()
When light passes through a colloidal solution, its path becomes clearly visible due to scattering of light by colloidal particles. This is called 'Tyndall effect'.

Generic 2

6 x 2 = 12

It is important to have a clean surface so that they are not covered by the gases of the air (O₂,N₂ ect.) and surface is available for adsorption of desired of desired gases.

The process of decomposition of an emulsion into its constituent liquids is called demulsification. Examples of demulsifiers are surfactants, ethylene oxide, etc.

The ester hydrolysis takes as follows:
\(\underset { Ester }{ RCOOR' } +\underset { Water }{ H_{ 2 }O } \rightleftharpoons \underset { Acid }{ RCOOH } +\underset { Alcohol }{ R'OH } \)
The acid produced in the reaction acts as catalyst (autocatalyst) for the reaction. Hence, the reaction becomes faster after some time.

Yes, the activity of enzymes is highly specific because they catalyse specific reaction and do not catalyse another. They can bind to specific substrate and not the other.

(a) Emulsification: The process of making an emulsion from an oil is termed emulsification.
(b) Emulsifying agent: The substances which stabilise emulsions are called emulsifying agents or emulsifier, e.g. soaps and detergents.
(c) Demulsifier: It is a substance which changes the emulsion into two separate layers.

10.

Sulfur sol can be prepared by oxidation of with the help\({ H }_{ 2 }S\) of Conc. \({ HNO }_{ 3 }\)
\({ H }_{ 2 }S\overset { [O] }{ \underset { { HNO }_{ 3 } }{ \rightarrow } } { H }_{ 2 }O+S\ \ { HNO }_{ 3 }\)
Bredig's Arc Method: Platinum (Pt) sol can be prepared by Bredig's arc method. Two Pt metal electrodes are taken through which high voltage is passed so that metal gets vaporized. When vapors are condensed, a colloidal solution of Pt in water is obtained.

Generic 3

5 x 3 = 15

11.

(i) Smaller the size of the particles of adsorbent larger will be the surface area and greater will be the extent of adsorption.
(ii) At constant temperature, the extent of adsorption increases with increase of pressure, rapidly in the beginning, relatively slow at moderate pressure and ultimately becomes independent of pressure.
(iii) At constant pressure, the physical adsorption decreases with increase of temperature whereas, the chemisorption first increases and then decreases.

12.

(i) Rough surface of a catalyst provides more surface area for adsorption.
(ii) So that unburnt charged carbon particles get settled between the charged plate leaving behind air free from pollutants.
(iii) Ne has higher critical temperature i.e., stronger Vander Waals forces therefore gets easily adsorbed.

13.

Characteristics of enzyme catalysis :
(i) High efficiency: A single molecule of enzyme can transform one million molecules of the reactant per minute.
(ii) High specificity: Each enzyme is specific for a given reaction.
(iii) Highly active under optimum temperature (25⁰-35⁰C).
(iv) Highly active under optimum pH.
(v) Enzyme activity increases in the presence of coenzymes.
(vi) Influence of inhibitors and poisons.
(vii) Enzyme do not alter final state of equilibrium.

14.

A colloidal state has larger surface area of sol particles and therefore, are more effectively adsorbed.Therefore the medicines in colloidal state are more easily assimilated or adsorbed and are more effective.

15.

(a) The charcoal powder will adsorb more gas because it has more surface area.
(b) (i) Bredig's Arc method: Take silver electrodes in form of electric arc in water and pass high voltage through it. A lot of heat will be generated which will vaporize silver metal into vapors which on condensing form silver sol.
(ii) Oxidation: Pass H2S gas through an aqueous solution of nitric acid. A colloidal solution of sulfur will be obtained.
\({ H }_{ 2 }S+[O]\xrightarrow [ Conc.H{ NO }_{ 3 } ]{ } { H }_{ 2 }O+S\)

Multiple Choice Question

5 x 1 = 5

16.

(d)
All the above are correct for different ranges of pressure

17.

18.

19.

(d)
Egg albumin

20.

(b)
\(\triangle G<0,\triangle S<0,\triangle H<0\)

Fill up / 1 Marks

5 x 1 = 5

21.

()
peptization

22.

()
1-1000

23.

()
adsorption isobar

24.

()
negative

25.

()
adsorption, absorption

Generic 5

2 x 5 = 10

26.

(i) Blood is a colloidal solution of albuminoid substance. The styptic action (blood stopping action) of alum is due to coagulation of blood forming a clot which stops further bleeding.
(ii) Values associated with Meera's decision are:
(a) Friendship
(b) Keen observation
(c) Applying knowledge of chemistry to daily life
(d) Responsibility
(e) Love and care.

27.

At P = 0.5 atm, \(\frac { x }{ m } kP1/n\ =\ 2\times { (0.5) }^{ 1 }=1.0\)