Surface Chemistry Test

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Surface Chemistry Test - 39

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Question 1
1 / -0

In Bredig's arc method, an electric arc is struck between the metal electrodes under the surface of water containing some stabilizing agent. The process involves:

A
mechanical dispersion

B
condensation

C
both dispersion and condensation

D
ultrasonic dispersion

Solution

In Bredig's arc method, an electric arc is struck between electrodes of the metal immersed in the dispersion medium. The intense heat produced vapourises the metal, which then condenses to form particles of colloidal size.

This process involves dispersion as well as condensation.

Colloidal sols of metals such as gold, silver, platinum, etc., are prepared by this method.

Hence, the correct answer is option $$\text{C}$$.
Question 2
1 / -0

Match the column I with column II with respect to applications of properties of colloids in different fields and mark the appropriate choice.
Column I Column II
(A) Coagulation (i) Colloidal medicines
(B) Adsorption (ii) Photographic films
(C) Electrophoresis (iii) Sewage disposal
(D) Emulsions (iv) Smoke precipitator

A
(A) $$\rightarrow$$ (iii), (B) $$\rightarrow$$ (i), (C) $$\rightarrow$$ (ii), (D) $$\rightarrow$$ (iv)

B
(A) $$\rightarrow$$ (ii), (B) $$\rightarrow$$ (iii), (C) $$\rightarrow$$ (i), (D) $$\rightarrow$$ (iv)

C
(A) $$\rightarrow$$ (iii), (B) $$\rightarrow$$ (i), (C) $$\rightarrow$$ (iv), (D) $$\rightarrow$$ (ii)

D
(A) $$\rightarrow$$ (i), (B) $$\rightarrow$$ (iv), (C) $$\rightarrow$$ (iii), (D) $$\rightarrow$$ (ii)

Solution

In water treatment, coagulation flocculation involves the addition of polymers that clump the small, destabilized particles together into larger aggregates so that they can be more easily separated from the water.

Medicines in colloidal form are easily absorbed by the body tissues and hence are more effective.

Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.

Photographic emulsion. Photographic emulsion is a light-sensitive colloid used in film-based photography.
Question 3
1 / -0

The separation of an emulsion into its constituent liquids is known as:

A
emulsification

B
protection of colloid

C
coagulation

D
demulsification
Solution
- Demulsification is the breaking of a crude oil emulsion into oil and water phases.
- Demulsification is used to separate various mixtures like water in oil and oil in water etc.
- It completely separates the constituent liquids and hence is the reverse of emulsification.
Question 4
1 / -0

Why is ferric hydroxide colloid positively charged when prepared by adding ferric chloride to hot water?

A
Due to precipitation of ferric hydroxide there is an excess of $$Fe^{3+}$$ ions.

B
Due to preferential adsorption of $$Fe^{3+}$$ ions by the sol of $$Fe(OH)_{3.}$$

C
Due to absence of any negatively charged ion.

D
Due to adsorption of $$OH^{-}$$ and $$CI^{-}$$ ions, the remaining sol has only $$Fe^{3+}$$ ions.

Solution

The adsorption of positively charged Fe3+ ions by the sol of hydrated ferric oxide results in positively charged colloid.
Question 5
1 / -0

Which of the following statements given about emulsions is incorrect?

A
The droplets in emulsions are often negatively charged and can be precipitated by electrolytes.

B
Emulsion can be diluted with any amount of the dispersed liquid. On the other hand, the dispersion medium when mixed, forms a separate layer.

C
Emulsions can be broken into constituent liquids by heating, freezing, centrifuging, etc.

D
Emulsions also show Brownian movement and Tyndall effect.
Solution
- Emulsions are liquid-liquid colloidal systems, i.e., the dispersion of finely divided droplets in another liquid.
- If a mixture of two immiscible or partially miscible liquids is shaken, a coarse dispersion of one liquid in the other is obtained which is called an emulsion.
- In emulsions, the droplets present are often negatively charged and can be precipitated by electrolytes.
- Emulsions can be broken down into its constituents by heating, freezing, centrifuging etc.
- Emulsions being a colloid shows both Tyndall effect and Brownian motion.
Hence, option $$B$$ is incorrect.
Question 6
1 / -0

The ratio of the number of moles of $$AgNO_{3}$$, $$Pb(NO_{3})_{2}$$ and $$Fe(NO_{3})_{3}$$ required for coagulation of a definite amount of a colloidal sol of silver iodide prepared by mixing $$AgNO_{3}$$ with excess of KI will be :

A
1 : 2 : 3

B
3 : 2 :1

C
6 : 3 : 2

D
2 : 3 : 6

Solution

With axcess of $$KI$$, colloidal particles will be $$[AgL]I^-$$
$$\xrightarrow [ 1\ mol ]{ [AgL]I^- } +\xrightarrow [ 1\ mol ]{ AgNO_3 } \rightarrow AgI \downarrow +AgI \downarrow +NO_3^-$$

$$\xrightarrow [ 2\ mol ]{ 2[AgL]I^- } +\xrightarrow [ 1\ mol ]{Pb(NO_3)_2 } \rightarrow 2AgI \downarrow +PbI_2 \downarrow +2NO_3^-$$

$$\underset { \begin{matrix} 3mole \\ 1mole \end{matrix} }{ 3[AgI]I^- } +\underset { \begin{matrix} 1mole \\ mole \end{matrix} }{ Fe(NO_3)_3 } \rightarrow 3AgI \downarrow +FeI_2 \downarrow +3NO_3^-$$
$$\therefore$$ Molar ratio required for coagulation of same amount of $$[AgI]I^-$$ is $$=1:\dfrac{1}{2}:\dfrac{1}{3}=6:3:2$$
Question 7
1 / -0

Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $$SnCl_{2}$$, formaldehyde, phenyl hydrazine, etc.
2$$AuCl_{3}$$ + 3$$SnCl_{2}$$ $$\rightarrow$$ 3$$SnCl_{4}$$ + $$2Au_{sol}$$
The above method is an example of:

A
reduction method

B
oxidation method

C
hydrolysis method

D
double decomposition method
Solution
- A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
- Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $$SnCl_2$$, formaldehyde, phenylhydrazine.
In the given reaction,
$$2AuCl_3 + 3SnCl_2 \rightarrow 3SnCl_4 + 2Au_{sol}$$
The oxidation state of $$Sn$$ is changing from -2 to -4. So,it is gaining electrons and hence the method is the reduction method.
Question 8
1 / -0

When a small quantity of $$FeCl_{3}$$ solution is added to the fresh precipitate of $$Fe(OH)_{3}$$, a colloidal sol is obtained. The process through which this sol is formed is known as:

A
exchange of solvent

B
chemical double decomposition

C
peptization

D
electrophoresis
Solution
- Peptization may be defined as the process of converting a precipitate into colloidal sol by shaking it with dispersion medium in the presence of a small amount of electrolyte.
- The electrolyte used for this purpose is called a peptizing agent.
- When a small quantity of $$FeCl_3$$ solution is added to fresh precipitate of $$Fe(OH)_3$$ the precipitate is converted into colloidal sol, which is nothing but the process of peptization.
Question 9
1 / -0

Which of the following is not an example of an emulsifying agent?

A
Proteins

B
Gums

C
Soaps

D
Electrolytes
Solution
Emulsions are liquid-liquid colloidal systems, i.e., the dispersion of finely divided droplets in another liquid.
If a mixture of two immiscible or partially miscible liquids is shaken, a coarse dispersion of one liquid in the other is obtained which is called emulsion.
Emulsions of oil in water are unstable and sometimes they separate into two layers on standing.
The emulsifying agent forms an interfacial film between suspended particles and the medium, which stabilises the Emulsion.
Examples of emulsifying agents are proteins, gums, natural and synthetic soaps,heavy metal salts of fatty acids, long chain alcohols, lampblack.
Here, electrolyte is not an emulsifying agent and hence is the correct option.
Question 10
1 / -0

Which of the following is not a correct match?

A
Butter - Oil in water type emulsion

B
Vanishing cream - Oil in water type emulsion

C
Milk - Oil in water type emulsion

D
Cream - Water in oil type emulsion
Solution
Emulsions are liquid-liquid colloidal systems, i.e., the dispersion of finely divided droplets in another liquid.

If a mixture of two immiscible or partially miscible liquids is shaken, a coarse dispersion of one liquid in the other is obtained which is called an emulsion.

Generally, there are two types of emulsions:
Oil in water type - Vanishing creams, Milk, etc.
Water in Oil type - Cream, Butter, etc.

Hence, option A is not a correct match.

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Column I	Column II
(A) Coagulation	(i) Colloidal medicines
(B) Adsorption	(ii) Photographic films
(C) Electrophoresis	(iii) Sewage disposal
(D) Emulsions	(iv) Smoke precipitator

Surface Chemistry Test - 39

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Surface Chemistry Test - 39

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Question 1

mechanical dispersion

condensation

both dispersion and condensation

ultrasonic dispersion

Solution

Question 2

(A) $$\rightarrow$$ (iii), (B) $$\rightarrow$$ (i), (C) $$\rightarrow$$ (ii), (D) $$\rightarrow$$ (iv)

(A) $$\rightarrow$$ (ii), (B) $$\rightarrow$$ (iii), (C) $$\rightarrow$$ (i), (D) $$\rightarrow$$ (iv)

(A) $$\rightarrow$$ (iii), (B) $$\rightarrow$$ (i), (C) $$\rightarrow$$ (iv), (D) $$\rightarrow$$ (ii)

(A) $$\rightarrow$$ (i), (B) $$\rightarrow$$ (iv), (C) $$\rightarrow$$ (iii), (D) $$\rightarrow$$ (ii)

Solution

Question 3

emulsification

protection of colloid

coagulation

demulsification

Solution

Question 4

Due to precipitation of ferric hydroxide there is an excess of $$Fe^{3+}$$ ions.

Due to preferential adsorption of $$Fe^{3+}$$ ions by the sol of $$Fe(OH)_{3.}$$

Due to absence of any negatively charged ion.

Due to adsorption of $$OH^{-}$$ and $$CI^{-}$$ ions, the remaining sol has only $$Fe^{3+}$$ ions.

Solution

Question 5

The droplets in emulsions are often negatively charged and can be precipitated by electrolytes.

Emulsion can be diluted with any amount of the dispersed liquid. On the other hand, the dispersion medium when mixed, forms a separate layer.

Emulsions can be broken into constituent liquids by heating, freezing, centrifuging, etc.

Emulsions also show Brownian movement and Tyndall effect.

Solution

Question 6

1 : 2 : 3

3 : 2 :1

6 : 3 : 2

2 : 3 : 6

Solution

Question 7

reduction method

oxidation method

hydrolysis method

double decomposition method

Solution

Question 8

exchange of solvent

chemical double decomposition

peptization

electrophoresis

Solution

Question 9

Proteins

Gums

Soaps

Electrolytes

Solution

Question 10

Butter - Oil in water type emulsion

Vanishing cream - Oil in water type emulsion

Milk - Oil in water type emulsion

Cream - Water in oil type emulsion

Solution

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