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Emulsions is a colloids in which dispersed phase and dispersion medium both are liquid. Emulsion are two type;

(i) Oil in water emulsion: Oil is disperse and water is disperse medium e.g. Milk, vanishing cream etc. 

(ii) Water in Oil emulsion: Here water is disperse phase and oil is disperse medium e.g. Butter, Cold cream etc.

Emulsion – Liquid – liquid colloidal system is known as Emulsion. 

There are two types of Emulsion. 

(a) O/W type - Oil dispersed in water. 

Eg: milk, vanishing cream. 

(b) W/O type – Water dispersed in oil. 

Eg: Butter & Cream. 

An emulsion is the colloidal dispersion in which both the dispersed phase and the dispersion mediums are liquids. 

They can be of two types:- 

(i) Emulsion of oil in water. 

(ii) Emulsion of water in oil.

Enthalpy of chemisorption is high (80-240 KJ mol^-1) as it involves chemical bond formation.

(i) Lyophilic Sols:
Colloidal sols that are formed by mixing substances such as gum, gelatin, starch etc. with a suitable liquid (dispersion medium) are called lyophilic sols. These sols are reversible in nature i.e. if two constituents of the sol are separated by any means (such as evaporation), then the sol can be prepared again by simply mixing the dispersion medium with the dispersion phase and shaking the mixture.

(ii) Lyophobic sols:
When substances such as metals and their sulphides etc. are mixed with the dispersion medium, they do not form colloidal sols. Their colloidal sols can be prepared only by special methods. Such sols are called lyophobic sols. These sols are irreversible in nature. For example: sols of metals.

Now, the stability of hydrophilic sols depends on two things the presence of a charge and the salvation of colloidal particles on the other hand, the stability of hydrophobic sols is only because of the presence of a charge. Therefore, the latter are very much less stable than the former. If the charge of hydrophobic sols is removed (by addition of electrolytes), then the particles present in them some closer and form aggregates leading to precipitation.

(i) Assertion and reason both are correct and the reason is correct explanation of assertion.

1. Colloidal solution of few substances like phosphorous or sulphur is obtained by the solutions in alcohol and pouring them into water.

2. As they are insoluble in water, they form colloidal solution.

P in alcohol + water → P_sol

1. The colloidal solutions due to their different methods ofpreparation may contain impurities.

2. If they are not removed, they may destabilise and precipitate the colloidal solution. This is called coagulation.

3. Hence the impurities mainly electrolytes should be removed to increase the stabilisation of colloid.

(d) Tollen’s test

(b) Exchange of solvent

1. Kidney malfunction results in the building up of electrolyte concentration within the blood to toxic levels. 

2. In the dialysis. recycling of patient’s blood is done through considerable length of semipermeable tube in an isotomic saline solution.

Glue can act as emulsifier

Purple of cassius is a purple pigment formed by the reaction of gold salts with tin (II) chloride. It has been used to impart red colouration as well as to determine the presence of gold as a chemical test.

(a) Both A and R are correct and R is the correct explanation of A.

(b) lyophilic colloids

1. Zsigmondy introduced the term “Gold number” as a measure of protective power of a colloid.

2. Gold number is defined as the number of milligrams of hydrophilic colloid that will just prevent the precipitation of 10 ml of gold sol on the addition of 1 ml of 10% NaCI solution.

(c) Protective colloids

Mercury sol is obtained by subjecting it to sound waves of frequency more than 20 kHz.

(c) (ii) only

(c) double decomposition

(d) peptisation

(b) Decomposition

Separating an emulsion in constituent liquids. Heating and freezing.

Dialysis: The process of dialysis is based on the fact that colloidal particles can not be diffused from parchment membrane or cell membrane and cell wall while the ions of electrolyte are diffused.

The colloidal solution taken in a bag made of cellophane or parchment. The bag is suspended in water. The impurities of electrolyte are diffused slowly towards outside and pure colloidal solution remains in dialysis apparatus. The process of the separating the paricles of colloids from those of crystalloids by means of diffusion through a suitable membrane is called dialysis.

Pig iron, cast iron and wrought iron.

I. Pig iron contains 4% carbon,

II. Cast iron contains 3% iron

III. Wrought iron contains 0.2-0.5% Carbon.

(c) oxidation

(a)  4 3 1 2

(a) Tyndall effect- scattering of light by colloidal particles by which path of beam becomes clearly visible. this effect is known as tyndal effect.

(b) Brownian movement- zig-zag motion of colloidal particles.

(c) Hardy Sehulze Law - Coagulating value of a coagulating ion is directly proportional to the charge on the ion.

e.g: Na⁺< Ca⁺⁺< Al³⁺ for negatively changed sol.

 Cl^- < CO₃^2- < PO₄^3- < [Fe (CN)₆]^4- for positive sol.

Gold sol is prepared by the reduction of auric chloride using formaldehyde.

2AuCl₃ + 3HCHO + 3H₂O → 2Au (sol) + 6HCI + 3HCOOH

Chlorine is extracted from brine by oxidation method

 NaCl(aq) → Na⁺ + Cl^-

At anode

2Cl^- + 2H₂O → Cl₂ + H₂ + 2OH^-

At cathode

2H⁺ + 2e^- → H₂

Gold sol is prepared by reduction of auric chloride using HCHO

(a) Gelatine sol

1. precipitation

2. flocculation

3. geLatine sol 

4. Zsigmondy 

5. CaCl₂ , AlCl₃ 

6. colloids 

7. Argyrol 

8. Silver sol 

9. chromium

10. Tollens reagent (or) Ammoniacal AgNO₃

1. formaldehyde

2. double decomposition

3. oxidation

4. coagulation

5. isotonic saline

6. nitro cellulose, alcohol and water 

7. 1 mi to llim diameter

8. disc or plate like

9. Brownian movement

10. coagulation

Metals are extracted by reduction method.

Zone refining is Si Or Ge.

1. emulsion

2. solid sol

3. benzene

4. 7000

5. mechanical dispersion 

6. George Bredig 

7. alkali hydroxide

8. stabilising agent 

9. mercury sol, mercury 

10. HCl

Liquation process.

Distillation method

(a) 4% solution of nitro cellulose in a mixture of alcohol and water

Principle - On passing electric current pure metal collected at cathode.

Method - Thick plate of impure metal is taken as anode and thin plate of pure metal is taken as cathode. Electrolyte is an aqueous salt solution of metal. On passing electric current pure metal is collected at cathode and impurities settle down as anode mud.

Reaction at anode M → Mⁿ⁺ + ne^-

Reaction at cathode Mⁿ⁺ + ne^- →  M

ZONE REFINING – Impurities are more soluble in the molten state than the pure metals i.e. on cooling pure metal crystallize out on cooling while impurities will remain behind.

ELECTROLYTIC REFINING – Pure metal deposit at cathode from electrolyte by passing electricity while crude metal from anode decompose to electrolyte.

(iii) Assertion is correct but reason is incorrect.

Brass- Cu 60%,Zn 40%

Bronze – Cu 80 %, Zn 10%, Sn 10 %

Alumina is filled in column during chromatographic method.

(iv) gas-gas

 Stationary phase and mobile phase.

(c) interface

(iii) homogeneous catalysis

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Check the below MCQ Question for class 12 Chemistry Surface Chemistry with Answers. MCQ Questions for class 12 Chemistry with Answers were prepared based on the newest exam pattern. 

Practice MCQ Question for Class 12 Chemistry chapter-wise

1. Tyndall effect confirms the

(a) gravity effect on the sol. particles
(b) light scattering by the sol. particles
(c) heterogeneous nature of sols
(d) Brownian motion of the sol. particles

2. Which one of the following is a lyophilic colloid?

(a) Milk
(b) Gum
(c) Fog
(d) Blood

3. Shape selective catalysis is a reaction catalysed by

(a) zeolite
(b) enzymes
(c) platinum
(d) Ziegler-Natta catalyst

4. Which of the following types of metals make the most efficient catalyst?

(a) Alkali metals
(b) Transition metals
(c) Inner transition metals
(d) Alkaline earth metals

5. The oxide of nitrogen which acts as a catalyst in lead chamber process is

(a) NO
(b) NO₂
(c) N₂O₄
(d) H₂O₅

6. The activity of an enzyme becomes ineffective

(a) at low temperature
(b) at atmospheric pressure
(c) at high temperature
(d) in aqueous medium

7. Which of the following can adsorb larger volume of hydrogen gas?

(a) Finely divided platinum
(b) Colloidal solution of palladium
(c) Small pieces of palladium
(d) A single metal surface of platinum

8. Which of the following gases present in a polluted area will be adsorbed most easily on the charcoal gas mask?

(a) H₂
(b) O₃
(c) N₂
(d) SO₂

9. Which kind of catalysis can be explained on the basis of adsorption theory?

(a) Homogeneous catalysis
(b) Heterogeneous catalysis
(c) Negative catalysis
(d) Auto catalysis

10. A colloidal system is which liquid is dispersed phase and solid is dispersion medium is classified as

(a) gel
(b) sol
(c) emulsion
(d) aerosol

11. Substances which behave as normal electrolytes solution at low concentration and exhibit colloids properties at higher concentration are called

(a) lyophilic colloids
(b) lyophobic colloids
(c) macromolecular colloids
(d) associated colloids

12. The formation of micelles takes place only above

(a) critical temperature
(b) Kraft temperature
(c) inversion temperature
(d) absolute temperature

13. Why is alum added to water containing suspended impurities?

(a) To make a colloidal solution
(b) To coagulate the suspended impurities
(c) To remove impurities of calcium and magnesium
(d) To protect the colloidal solution from gening precipitated

14. Movement of dispersion medium under the influence of electric field is known as

(a) electrodialysis
(b) electrophoresis
(c) electroosmosis
(d) cataphoresis

15. The physical adsorption of gases on the solid surface is due to:

(a) Covalent bond
(b) Hydrogen bond
(c) Ionic bond
(d) Van der waal's forces

16. The electrical charge on a colloidal particle is observed by:

(a) Ultramicroscope
(b) Scattering
(c) Brownian movement
(d) Electrophoresis

17. Purple of cassius is colloidal solution of :

(a) Silver
(b) Lead
(c) Gold
(d) Mercury

18. Milk is colloid in which :

(a) Liquid is dispersed in liquid
(b) Gas is dispersed in liquid
(c) Sugar is dispersed in water
(d) Solid is dispersed in liquid

19. Which of the following is a lyophobic colloidal solution?

(a) Aqueous starch solution
(b) Aqueous protein solution
(c) Gold solution
(d) Polymer solvent in some organic solvents

20. Butter is a colloid form in which:

(a) fat is dispersed in solid casein
(b) fat globules are dispersed in water
(c) water is dispersed in fat
(d) suspension of casein is in water

21. Negative catalyst or inhibitor is one:

(a) which retards the rate of reaction
(b) takes the reaction in forward direction
(c) promotes the side reaction
(d) none of the above

22. Alum helps in purifying water by:

(a) Forming Si complex with clay particles
(b) Sulphate part which combines with the dirt and removes it
(c) Aluminium which coagulates the mud particles
(d) Making mud water soluble

23. Milk can be preserved by adding a few drops of:

(a) Formic acid solution             
(b) Formaldehyde solution
(c) Acetic acid solution             
(d) Acetaldehyde solution

24. Clouds, mist, fog and aerosols are colloidal solution of:

(a) solid in a gas
(b) gas in a solid
(c) liquid in a gas
(d) gas in a liquid

25. Gold number is the index for:

(a) Protective power of lyophilic colloid
(b) Purity of gold
(c) Metallic gold
(d) Electroplated gold

Answer :

1. Answer : (c) heterogeneous nature of sols

Explanation: Tyndall effect confirms the heterogeneous nature of the colloidal solution.it is observed due to the scattering of dust particles. Tyndall effect is used to distinguish between the true solution and the colloidal solution.

2. Answer : (b) Gum

Explanation: In such solids, the dispersed phase does not easily precipitate and the sols are quite stable. These sols are reversible in nature.If water is used as the dispersion medium, lyophilic sols are called hydrophilic sols. Starch, gum, gelatin, egg albumin etc.

3. Answer : (a) zeolite

Explanation: The shape-selective catalysis is a reaction catalysed by Zeolites. Because the structure of Zeolites is like a honeycomb. Hence it is used as the catalyst in the chemical reaction. Zeolites are especially used as Shape-selective catalysis.

4. Answer : (b) Transition metals

Explanation: The transition metals are considered to make the most efficient catalysts. This is because, when these metals are with suitable reactants, they form unstable intermediate products that can lower the activation energy and thereby making the reaction faster.

5. Answer : (a) NO

Explanation: The process of producing sulfuric acid by oxidizing sulfur dioxide with moist air, using gaseous nitrogen oxides as catalysts, is known as Lead chamber process. This reaction takes place primarily in a series of large, boxlike chambers of sheet lead.

6. Answer : (c) at high temperature

Explanation: Enzymes are effective only at optimum temperature. They become ineffective at very high temperature.

7. Answer : (b) Colloidal solution of palladium

Explanation: An excellent absorbed hydrogen gas is palladium. Therefore, colloidal solutions of palladium could adsorb greater volume of hydrogen gas as the surface area of palladium is the most colloidal solution of palladium.

8. Answer : (d) SO₂

Explanation: The amount of gas adsorbed by a solid depends on the nature of gas. In general, easily liquefiable gases. Easily liquefiable gases will have higher critical temperatures are readily adsorbed as van der Waals’ forces are stronger near the critical temperatures.SO₂ is having the maximum critical temperature and hence it gets adsorbed most easily on the charcoal gas mask.

9. Answer : (b) Heterogeneous catalysis

Explanation: Adsorption theory of Heterogeneous catalyst is adsorption theory of catalysis, the reactions in their gaseous state on in their dissolved state in any solution gets adsorbed on the surface of
a suitable catalyst in its solid state.

10. Answer : (a) gel

Explanation: A colloidal system in which liquid is a dispersed phase and solid is dispersion medium is known as Gel. Example-Cheese, jellies.

11. Answer : (d) associated colloids

Explanation: Associated colloids are substances which at low concentrations behave as normal strong electrolytes, but at higher concentrations exhibit colloidal behaviour due to the formation of aggregates.
The aggregated particles formed are called micelles. The formation of micelles takes place only above a particular temperature called Kraft temperature and above a particular concentration called critical micelle concentration.

12. Answer : (b) Kraft temperature

Explanation: The formation of micelles takes place only above a particular temperature called Kraft temperature (TK).

13. Answer : (b) To coagulate the suspended impurities

Explanation: When alum is added to raw water it reacts with the bicarbonates alkalinities present in water and forms a gelatinous precipitate. It neutralizes all the suspended impurities of water resulting in their coagulation.

14. Answer : (c) electroosmosis

Explanation: When movement of particles (electrophoresis) is prevented by some suitable means, it is observed that the dispersion medium begins to move in an electric field. This phenomenon is termed as electroosmosis.

15. Answer : (d) Van der waal's forces

Explanation: When the force of attraction existing between adsorbate and adsorbent are weak Vanderwaal forces of attraction, the process is called Physical Adsorption or Physisorption. When the force of attraction existing between adsorbate and adsorbent are chemical forces of attraction or chemical bond, the process is called Chemical Adsorption.

16. Answer : (d) Electrophoresis

Explanation: Colloidal particles possess some type of electric charge. The migration of colloidal particles under the influence of an electric field is known as electrophoresis.

17. Answer : (c) Gold

Explanation: Gold is dissolved in the aqua medium and it further reduces to give a purple precipitate. Therefore, purple of cassius is a colloidal sol of gold.

18. Answer : (a) Liquid is dispersed in liquid

Explanation: Milk is an emulsified colloid of Liquid is dispersed in liquid where liquid butterfat globules dispersed within a water-based solution. 

19. Answer : (c) Gold solution

Explanation: Gold sol is a lyophobic sol. Gold particles have very less affinity towards dispersion medium, hence its sol can be easily coagulated.

20. Answer : (c) water is dispersed in fat

Explanation: A colloid is a mixture where a particular substance is trapped in a given dispersion medium but do not get mixed chemically. Butter is a colloidal formed when water is dispersed in fat.

21. Answer : (a) which retards the rate of reaction

Explanation: The catalyst which decreases the rate of reaction is known as inhibitor or negative catalyst and the process is known as negative catalysis or inhibition. Negative catalysts are useful to slow down or stop any unwanted reactions.

22. Answer : (c) Aluminium which coagulates the mud particles

Explanation: Alum is added to water in order to destabilize the mud particles suspended in it. This process is known as coagulation. Alum helps in purifying water by aluminium which helps to coagulate the mud particles.

23. Answer : (b) Formaldehyde solution

Explanation: Formaldehyde solution is an emulsifier which is added in the milk as it acts as a preserving agent for the milk.

24. Answer : (c) liquid in a gas

Explanation: Fog or cloud is a colloidal dispersion of water droplets in a dispersion medium of gas. When the dispersion medium is gas, the dispersed phase can be solid or liquid but not gas.

25. Answer : (a) Protective power of lyophilic colloid

Explanation: The Gold Number is the minimum weight (in milligrams) of a protective colloid required to prevent the coagulation of 10 ml of a standard hydro gold sol when 1 ml of a 10% sodium chloride solution is added to it.

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