Surface Chemistry Test

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Surface Chemistry Test - 17

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Question 1
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Peptization is a process of :

A
precipitating colloidal particles.

B
purifying colloidal particles.

C
dispersing the precipitate into colloidal state.

D
none of the above.

Solution

Peptization is a process of passing of a precipitate into colloidal particles on adding suitable electrolyte. The electrolyte added is known as peptizing agent.
For example: A reddish brown colored colloidal solution is obtained by adding small quantity of ferric chloride solution to the freshly precipitated ferric hydroxide.
Question 2
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Tanning of leather is the :

A
colouring of leather by chemicals

B
drying process to make the leather hard

C
polishing of leather to make it look attractive

D
coagulative hardening of the leather by chemicals

Solution

Tanning is the process that converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. The principal difference between raw hides and tanned hides is that raw hides dry out to form a hard inflexible material that can putrefy when re-wetted (wetted back), while tanned material dries out to a flexible form that does not become putrid when wetted back. A large number of different tanning methods and materials can be used. The choice is ultimately dependent on the end application of the leather. The most commonly used tanning material is chromium, which leaves the leather, once tanned, a pale blue colour (due to the chromium), this product is commonly called wet blue.
Question 3
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Gelatin is often used as an ingredient in the manufacture of ice-cream. The reason for this is :

A
to prevent the formation of a colloid.

B
to stabilize the colloid and prevent crystal growth.

C
to cause the mixture to solidify.

D
to improve the flavour.

Solution

Gelatin is a translucent, colourless, brittle (when dry), flavourless foodstuff derived from collagen obtained from various animal by-products. It is commonly used as a gelling agent in food, pharmaceuticals. Substances containing gelatin or functioning in a similar way are called gelatinous. Gelatin is an irreversibly hydrolyzed form of collagen. It is often used as an ingredient in the manufacture of ice-cream to stabilize the colloid and prevent crystal growth and works as protective colloid.
Question 4
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The rate of decomposition of aldehyde $$(CH_3CHO)$$ into $$CH_4$$ and $$CO$$ in presence of $$I_2$$ at 800 K follows the rate law: $$r=K[CH_3CHO][I_2]$$. The decomposition is believed to go to the two step mechanism:

$$CH_3CHO+I_2\rightarrow CH_3I+HI+CO$$

$$CH_3I+HI\rightarrow CH_4+I_2$$

What is the catalyst for the reaction? Which of the two steps is the slower one?

A
$$HI, I^{st} \ step$$

B
$$I_2, I^{st} \ step$$

C
$$HI, II^{st}\ step$$

D
$$I_2, II^{st}\ step$$

Solution

Iodine is consumed in the first step and formed in the second step. Hence, iodine is the catalyst. The rate law expression contains the concentrations of acetaldehyde and iodine which appear in the first step. Hence, the first step is the slower step. It is the rate determining step.
Question 5
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Rate of reaction (r) is plotted against temperature (T) for an enzyme catalysed reaction. Which of the following is correct representation?

A

B

C

D

Solution

Option (B) is correct.

Enzyme catalysed reactions have optimium temperature range $$35^oC$$. As the temperature increases, the speed of movement of substrate and enzymes molecules also continues to increase. But above certain temperature ($$35^oC$$) called as optimum temperature, enzymes gets denatured.
Question 6
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Milk is an example of :

A
Aquasol

B
True solution

C
Aerosol

D
Emulsion

Solution

Aerosols are a colloidal solution of liquid and gas.

A true solution is a homogeneous solution in which the solute particles have diameters less than $$10^{-7}$$cm.

In an emulsion, one liquid (the dispersed phase) is dispersed in the other liquid (the continuous phase).

Hence, milk is an example of emulsion.
Question 7
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Substances, which are added to soaps change their properties in order to make them more useful for a particular application, are called ___.

A
fillers

B
absorbant

C
reagent

D
none

Solution

Substances, which are added to soaps change their properties in order to make them more useful for a particular application, are called fillers.
Fillers make the soap harder, harsher on the skin and lower the cost.
Question 8
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Directions For Questions

Emulsions are also called the colloidal solutions in which the dispersed phase as well as dispersion medium are liquids. It may be oil-in-water or water-in-oil type. Emulsifiers can be used to stabilize the emulsion. Soaps, detergents, proteins and gums are used as emulsifiers.

...view full instructions

Butter is an emulsion of type :

A
water in oil

B
oil in water

C
oil and oil

D
none of the above

Solution

Oil in water (o/w) type : In these emulsions, oil forms the dispersed phase and water, the dispersion medium. For example, milk, vanishing cream, etc. These are also called aqueous emulsions.
Water in oil (w/o) type : In these emulsions, water is in the dispersed phase and oil in the dispersion medium. For example, butter, cold cream etc. are also called oil emulsions.
Question 9
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Directions For Questions

Substances which alter the velocity of a reaction by mere presence without undergoing any change in mass and composition are termed catalysts and the phenomenon is known as catalysis.

...view full instructions

Which is incorrect for a catalyst?

A
A catalyst can initiate a reaction

B
A catalyst remains unchanged in quality and composition at the end of reaction

C
It does not alter the position of equilibrium in a reversible reaction

D
Catalysts are sometimes very specific in reaction

Solution
Question 10
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A freshly obtained precipitate of $$SnO_2$$ is peptized by little of $$KOH$$ to give a sol. The sol particles may be represented as :

A
$$[SnO_2]K^{+}$$

B
$$[SnP_2]OH^{-}$$

C
$$[SnO_2]Sn^{4+}$$

D
$$[SnO_2]SnO_3^{2-}$$

Solution

The reaction is as follows:
$$SnO_2(s)+2KOH(aq)\rightarrow K_2SnO_3(aq)+H_2O$$
$$SnO_3^{2-}$$ ions would be preferentially adsorbed by $$SnO_2$$ particles.