Tamilnadu State Board New Syllabus Samacheer Kalvi 12th Chemistry Guide Pdf Chapter 10 Surface Chemistry Text Book Back Questions and Answers, Notes.

## Tamilnadu Samacheer Kalvi 12th Chemistry Solutions Chapter 10 Surface Chemistry

### 12th Chemistry Guide Surface Chemistry Text Book Questions and Answers

Part – I Text Book Evaluation

Question 1.
For freudlich isotherm a graph of log $$\frac{x}{m}$$ is plotted against log P. The slope of the line and its y – axis intercept respectively corresponds to
(a) $$1 / n$$, k
(b) log $$1 / n$$, k
(c) $$1 / n$$, log k
(d) log $$1 / n$$, log k
(c) $$1 / n$$, log k
$$\frac{x}{m}$$ = $$\mathrm{k} \cdot \mathrm{p}^{1 / \mathrm{n}}$$
log$$(\frac{x}{m})$$ = log k + $$\frac { 1 }{ n }$$log p
y = c + mx
m = $$\frac { 1 }{ n }$$ and c = log k

Question 2.
Which of the following is incorrect for physisorption?
(a) reversible
(b) increases with increase in temperature
(d) increases with increase in surface area
(b) increases with increase in temperature

Question 3.
Which one of the following characteristics are associated with adsorption?
(a) ∆G and ∆H are negative but ∆S is positive
(b) ∆G and ∆S are negative but ∆H is positive
(c) ∆G is negative but ∆H and ∆S are positive
(d) ∆G. AH and ∆S all are negative.
(d) ∆G, ∆H and ∆S all are negative.
Adsorption leads to decrease in randomness (entropy).i.e. ∆S < 0 for the adsorption to occur, ∆G should be – ve. We know that ∆G = ∆H – T∆S if ∆S is – ve, T∆S is + ve. It means that ∆G will become negative only when ∆H is – ve and ∆H > T∆S

Question 4.
Fog is colloidal solution of ……………..
(a) solid in gas
(b) gas in gas
(c) liquid in gas
(d) gas in liquid
(c) liquid in gas
dispersion medium-gas, dispersed phase-liquid

Question 5.
Assertion: Coagulation power of Al3+ is more than Na.
Reason: greater the valency of the flocculating ion added, greater is its power to cause precipitation
(a) if both assertion and reason are true and reason is the correct explanation of assertion.
(b) if both assertion and reason are true but reason is not the correct explanation of assertion.
(c) assertion is true but reason is false
(d) both assertion and reason are false
(a) if both assertion and reason are true and reason is the correct explanation of assertion. (Hardy-Sechuize nile)

Question 6.
Statement: To stop bleeding from an injury, ferric chloride can be applied. Which comment about the statement is justified?
(a) It is not true, ferric chloride is a poison.
(b) It is true, Fe3+ ions coagulate blood which is a negatively charged sol
(c) It is not true; ferric chloride is ionic and gets into the blood stream.
(d) It is true, coagulation takes place because of formation of negatively charged sol with Cl.
(b) It is true, Fe3+ ions coagulate blood which is a negatively charged sol

Question 7.
Hair cream is …………..
(a) gel
(b) emulsion
(c) solid sol
(d) sol.
(b) emulsion
Emulsion dispersed phase, Dispersion medium -liquid

Question 8.
Which one of the following is correctly matched?
(a) Emulsion – Smoke
(b) Gel – butter
(c) foam – Mist
(d) whipped cream – sol
(b) Gel – butter

Question 9.
The most effective electrolyte for the coagulation of As2S3 Soils
(a) NaCl
(b) Ba(NO3)2
(c) K3[Fe(CN)6]
(d) AI2(SO4)3
(d) AI2(SO4)3

Question 10.
Which one of the is  not a surfactant?
(a) CH3 – (CH2)15 – N – (CH3)2CH2Br
(b) CH3 – (CH2)15 – NH2
(c) CH3 – (CH2)16 – CH2OSO2 – Na+
(d) OHC – (CH2)14 – CH2 – COONa+
(b) CH3 – (CH2)15 – NH2

Question 11.
The phenomenon observed when a beam of light is passed through a colloidal solution is ………….
(a) Cataphoresis
(b) Electrophoresis
(c) Coagulation
(d) Tyndall effect
(d) Tyndall effect-scattering of light

Question 12.
In an electrical field, the particles of a colloidal system move towards cathode. The coagulation of the same sol is studied using K2SO4
(i). Na3PO4
(ii). K4[Fe(CN)6]
(iii). and NaCI
(iv). Their coagulating power should be …………..
(a) II > I >IV > III
(b) III > II > I > IV
(c) I > II > III > IV
(d) none of these
(b) III > II > I > IV

Question 13.
Collodion is a 4% solution of which one of the following compounds in alcohol – ether mixture?
(a) Nitroglycerine
(b) Cellulose acetate
(c) Glycoldinitrate
(d) Nitrocellulose
(a) Nitrocellulose
pyroxylin (nitro cellulose)

Question 14.
Which one of the following is an example for homogeneous catalysis?
(a) manufacture of ammonia by Haber’s process
(b) manufacture of sulphuric acid by contact process
(c) hydrogenation of oil
(a) Hydrolysis of sucrose in presence of all HCI
(a) Hydrolysis of sucrose in presence of all HCl
Both reactant and catalyst are in same phase. i.e. (1)

Question 15.
Match the following.

 A)V2 O5 i) High density polyethylene B) Ziegler – Natta ii) PAN C) Peroxide iii) NH3 D) Finely divided Fe iv) H2SO4

(a) (iv) (i) (ii) (iii)

Question 16.
The coagulation values in millimoles per litre of the electrolytes used for the coagulation of AS2S3 are given below
(I) (NaCl) = 52
(II) (BaCl) = 0.69
(III) (MgSO4) = 0.22
The correct order of their coagulating power is ……….
(a) III > II > I
(b) I > II > III
(c) I >III > II
(d) II > III > I
(a) III > II > I

Question 17.
Adsorption of a gas on solid metal surface is spontaneous and exothermic, then ……………
(a) ∆H increases
(b) ∆S increases
(c) ∆G increases
(d) ∆S decreases
(a) ∆S decreases – ∆S is -ve

Question 18.
If x is the amount of adsorbate and m is the amount of adsorbent, which of the following relations is not related to adsorption process?
(a) x/m = f(P) at constant T
(b) x/m = f(T) at constant P
(c) P = f(T) at constant x/m
(d) x/m = PT
(d) x/m = mPT

Question 19.
On which of the following properties does the coagulating power of an ion depend?
(a) Both magnitude and sign of the charge on the ion.
(b) Size of the ion alone
(c) the magnitude of the charge on the ion alone
(d) the sign of charge on the ion alone.
(a) Both magnitude and sign of the charge on the ion.

Question 20.
Match the following.

 A) Pure nitrogen i) Chlorine B) Haber process ii) Sulphuric acid C) Contact process iii) Ammonia D) Deacons process iv) Sodium azide (or) Barium azide

Question 1.
Give two important characteristics of physisorption.
Important characteristics of physisorption:

1. It is reversible
2. It has low heat of adsorption
3. It has weak van der Waals forces of attraction with the adsorbent.
4. It increases with an increase in pressure.
5. It forms multi molecular layer.

Question 2.
Differentiate physisorption and chemisorption.

1. It is very slow
2. It is very specific depends on nature of adsorbent and adsorbate.
3. chemical adsorption is fast with increase pressure, it can not alter the amount.
4. When temperature is raised chemisorption first increases and then decreases.
5. Chemisorption involves transfer of electrons between the adsorbent and adsorbate, Heat of adsorption is high i.e., from 40 – 400kJ/mole.
6. Monolayer of the adsorbate is formed.
7. Adsorption occurs at fixed sites called active centres. It depends on surface area.
8. Chemisorption involves the formation of activated complex with appreciable activation energy.
10. It is irreversible.

1. It is instantaneous
2. It is non-specific
3. In Physisorption. when pressure increases the amount of adsorption increases.
4. Physisorption decreases with increase in temperature.
5. No transfer of electrons
6. Heat of adsorption is low in the order of 40kJ/mole.
8. It occurs on all sides.
9. Activation energy is insignificant.
10. It is reversible.

Question 3.
In case of chemisorption, why adsorption first increases and then decrease with temperature?
1. Chemisorption involves high activation energy so it is also referred to as activated adsorption.

2. It is found in chemisorption that it first increases and then decreases with an increase in temperature. When adsorption is plotted, the graph first increases and then decreases with temperature.

3. The initial increase illustrates the requirement of activation of the surface for adsorption is due to fact that the formation of activated complex requires certain energy. But later it decreases at high temperature is due to desorption as the kinetic energy of the adsorbate increases (exothermic nature)

Question 4.
Which will be adsorbed more readily on the surface of charcoal and why; NH3 or CO2?
1. The gases having low critical temperature are adsorbed slowly, while gases with high critical temperature are adborbed readily.

2. Among CO2, and NH3, NH3 will be more readily adsorbed on the surface of the charcoal. This is because the critical temperature of ammonia gas is quite high than the CO2. Hence, it easily combines with the materials than the CO2 whether it is solid, liquid or any gases.

Question 5.
Heat of adsorption is greater for chemisorptions than physisorption. Why?
Chemisorption has higher heat of adsorption. because in chemisorption the chemical bonds are much stronger. In adsorbed state the adsorbate is hold on the surface of adsorbent by attractive forces (bond). And chemisorption is irreversible one. Therefore, heat of adsorption is greater for chenil sorptions than physisorption. Chemisorption, heat of adsorption range 40 – 400kJ/mole.

Question 6.
In a coagulation experiment 10 mL of a colloid (X) is mixed with distilled water and 0.1M solution of an electrolyte AB so that the volume is 20 mL. It was found that all solutions containing more than 6.6 mL of AB coagulate with in 5 minutes. What is the flocculation values of AB for sol (X)?
A minimum of 6.6mL of AB is required to coagulate the sol. The moles of AB in the sol is
$$\frac{6.6 \times 0.01}{20}$$ = 0.033 moles
This means that a minimum of 0.033 moles or 0.0033 x 1000 = 3.3 milli moles are required for coagulating one litre of sol. Flocculation value of AB for X = 3.3

Question 7.
Peptising agent is added to convert precipitate into colloidal solution. Explain with an example.
1. Ions either positive or negative of peptizing agent (electrolyte) are adsorbed on the particles of precipitate. They repel and hit each other and break the particles of the precipitate into colloidal size.

2. For example, when we add a small volume of very dilute hydrochloric acid solution peptising agent to a fresh precipitate of a silver chloride, it leads to formation of silver chloride colloidal solution,

Question 8.
What happens when a colloidal sol of Fe(OH)3 and As2S3 are mixed?
On mixing Fe(OH)3 positive sol and As2S3 negative sol, mutual coagulation occurs which causes precipitation. When this sol got mixed with each other, due to Fe3+ and S2- ions neutralisation of charges will happen, and precipitate will be formed.
Fe(OH)3 + As2S3 → Fe2S3 + As(OH)3

Question 9.
What is the difference between sol and gel?
Sol

1. The liquid state of a colloidal solution is called a sol.
2. The sol does not have a definite structure.
3. The dispersion medium of the sol may be water.
4. The sol can be converted to gel by cooling The sol can be easily dehydrated.
5. The viscosity of the sol is very low.
6. Sol is categorized into lyophobic and lyophilic sols.
7. Example: Blood

Gel

1. The solid or semi-solid state of a colloidal solution is called gel.
2. The gel possesses a honeycomb-like structure.
3. The dispersion medium of gel will be hydrated colloid particles.
4. The gel can be converted to sol by heating.
5. The gel cannot be dehydrated.
6. The viscosity of the gel is very high.
7. There is no such classification of gel.
8. Example: Fruit jelly, cooked gelatin jelly.

Question 10.
Why are lyophillic colloidal sols are more stable than lyophoblic colloidal sol?
1. A lyophilic colloidal sols are stable due to the charge and the hydration of sol particles.

2. Lyophilic sols are more stable than lyophobilc sols because they are highly hydrated in the solution. And since more is the hydration more will be its stability.

3. Lyophilic sols are stabilized by electrostatic charge and hydration whereas lyophobic sols are only stabilized by charge, so they easily gets coagulated and requires a stabilising agent. Hence, lyophilic sols are more stable than lyophobilc sols.

Question 11.
Addition of Alum purifies water. Why?
Purification of drinking water is activated by coagulation of suspended impurities in water using alums containing Al3+. That is why we are adding to purify water.

Question 12.
What are the factors which influence the adsorption of a gas on a solid?
Factors that influence the adsorption of a gas on a solid is as follows:
1. Nature of the gas:
Easily liquefiable gases such as NH3, HCl etc are adsorbed to a great extent in comparison to gases such as H2, O2 etc. This is because van der Waal’s forces are stronger is easily liquifiable gases.

2. Surface area of the solid:
The greater the surface area of the adsorbent, the greater is the adsorption of gas on the solid surface.

3. Effect of pressure:
Adsorption is a reversible process and is accompanied by a decrease in pressure. Therefore, adsorption increases with an increase in pressure.

4. Effect of temperature:
Adsorption is an exothermic process. Thus in accordance with Le – Chatelier’s principle, the magnitude of adsorption decreases with an increase in temperature.

Question 13.
What are enzymes? Write a brief note on the mechanism of enzyme catalysis.
Enzymes are complex protein molecules with three-dimensional structures. They catalyse the chemical reaction in a living organism. They are often present in colloidal state and extremely specific in catalytic action.

Each enzyme produced in a particular living cell can catalyse a particular reaction in the cell. Mechanism of enzyme catalysis: Mechanism of enzyme catalysed reaction is known as lock and key mechanism.
1. Enzymes arc highly specific in their action.

2. This specificity is due to the pressure of active sites. The shape of active site of any given enzyme is like cavity such that only a specific substrate can fit into it.

In the same way a key fits into lock. The specific binding needs to the formation of an enzyme-substrate complex which accounts for high specificity of enzyme catalysed reactions.

3. Once the proper orientation is attained the substrate molecules reacts to form the product in two steps.

4. Since product molecules do not have any affinity for the enzyme they leave the enzyme surface making room for fresh substrate.

step 1: Formation of the enzyme-substrate complex

Step 2: Dissociation of the enzyme-substrate complex to form product

The rate of the formation of the product depends upon the concentration of ES.

Question 14.
What do you mean by activity and selectivity of catalyst?
1. Activity of Catalyst:
The activity of a catalyst is its ability to increase the rate of a particular reaction, Chemisorption is the main factor in deciding the activity of a catalyst. The adsorption of reactants in the catalyst surface should be neither too strong nor too weak. It should just be strong enough to make the catalyst active.

2. Selectivity of the catalyst:
The ability of the catalyst to direct a reaction to yield a particular product is referred to as the selectivity of the catalyst. For example, by using different catalysts, we can get different products for the reaction between H2 and CO.

Question 15.
Describe some features of catalysis b Zeoliles.
1. Zeolites are microporous, crystalline, hydrated aluminosilicates, made of silicon and aluminium tetrahedra.

2. There are about 50 natural zeolites and 1 50 synthetic zeolites. As silicon is tetravalent and aluminium is trivalent, the zeolite matrix carries extra negative charge. To balance the negative charge, there are extra framework cations for example, H+ or Na+ ions.

3. Zeolites earring protons are used as solid acids, catalysis and they are extensively used in the petrochemical industry for cracking heavy hydrocarbon fractions into gasoline, diesel,etc.

4. Zeolites earring Na ions are used as basic catalysis.

5. One of the most important applications of zeolites is their shape selectivity. In zeolites, the active sites namely protons are lying inside their pores. So, reactions occur only inside the pores of zeolites.

Question 16.
Give three uses of emulsions.

1. The cleansing action of soap is due to emulsions.
2. It is used in the preparation of vanishing cream.
3. It is used in the preparation of cold liver oil.

Question 17.
Why does the bleeding stop by rubbing moist alum?
Blood is a colloidal sol. When we nib the injured part with moist alum then coagulation of blood takes place. Hence main reason is coagulation, which stops the bleeding. Therefore bleeding stop by rubbing moist alum.

Question 18.
Why is desorption important for a substance to act as good catalyst?
Desorption is important for a substance to act as a good catalyst, so that after the reaction, the products found on the surface separate out (desorbed) to create free surface again for other reactant molecules to approach the surface and react. If desorption does not occur then other reactants are left with no space on the surface of the catalyst for adsorption and the reaction will stop.

Question 19.
Comment on the statement: Colloid is not a substance but it is a state of the substance.
The statement is true. Because the same substance may exist as a colloid under certain conditions and as a crystalloid under certain other conditions. For example. NaCl in water behaves as a crystalloid while in benzene, it behaves as a colloid. Similarly, dilute soap solution behaves

like a crystalloid while concentrated solutions behave as a colloid. It is the size of the particles which matters. That is the state in which the substance exists. If the size of the particles lies in the range 1 nm to 1oo nm, it is in the colloidal state.

Question 20.
Explain any one method for coagulation
The flocculation and setting down of the soil particles is called coagulation. Various method of coagulation are given below:

2. Electrophoresis
3. Mining oppositely charged sols
4. Boiling.

A negative ion causes the precipitation of positively charged sol and vice versa. When the valency of ion is high, the precipitation power is increased. For example, the precipitation power of some cations and anions varies in the following order
Al3+ > Ba2+ > Na+, Similarly [Fe(CN)6]-3 > SO4-2 > Cl
The precipitation power of electrolyte is determined by finding the minimum concentration (millimoles / lit) required to cause precipitation of a sol in 2hours. This value is called flocculation value. The smaller the flocculation value greater will be precipitation.

Question 21.
Write a note on electroosmosis.
Electro osmosis:
A sol is electrically neutral. Hence the medium carries an equal but opposite charge to that of dispersed particles. When sol particles are prevented from moving, under the influence of electric field the medium moves in a direction opposite to that of the sol particles. This movement of dispersion medium under the influence of electric potential is called electro-osmosis.

Question 22.
Write a note on catalytic poison
Catalytic poison:
Certain substances when added to a catalysed reaction, decreases or completely destroys the activity of catalyst and they are often known as catalytic poisons. For example, In the reaction,
2SO2 + O2 → 2SO3 with a Pt catalyst, the poison is AS2O3.
i.e., AS2O3 destroys the activity of pt. AS2O3 blocks the activity of the catalyst. So, the activity is lost.

Question 23.
Explain intermediate compound formation theory of catalysis with an example.
The intermediate compound formation theory:
A catalyst acts by providing a new path with low energy of activation. in homogeneous catalysed reactions a catalyst may combine with one or more reactant to form an intermediate which reacts with other reactant or decompose to give products and the catalyst is regenerated.

Consider the reactions:
A + B → AB ……………(1)
A + C → AC (intermediate) ………….(2)
C is the catalyst
AC + B → AB + C …………(3)
Activation energies for the reactions (2) and (3) are lowered compared to that of (1). Hence the formation and decomposition of the intermediate accelerate the rate of the reaction.
Example:
The mechanIsm of Fridel crafts reaction is given below

The action of catalyst is explained as follows .

This theory describes,

1. The specificity of a catalyst.
2. The increase in the rate of the reaction with increase in the concentration of a catalyst.

Limitations

1. The intermediate compound theory fails to explain the action of catalytic poison and activators (promoters).
2. This theory is unable to explain the mechanism of heterogeneous catalysed reactions.

Question 24.
What is the difference between homogenous and hetrogenous catalysis?
Hornogenous Catalysis:

1. In a catalysed reaction the reactants, products and catalyst are present in the same phase.
2. For example.

Hence NO act as catalyst.
3. Homogeneous catalysis explained by intermediate compound formation theory.

Heterogeneous Catalysis:

1. In a reaction, the catalyst is present in a different phase. i.e., catalyst is not present in the same phase as that of reactants and products.
2. For example.

Hence Pt(s) act as catalyst.
3. Hetenogeneous catalysis explained by adsorption theory.

Question 25.
Langmuir explained the action of catalyst in heterogeneous catalysed reactions based on adsorption.
This theory explains heterogeneous catalysis.
The reactant molecules are adsorbed on the catalytic surface, so heterogeneous catalysis is also called as contact catalysis.
When the reactants are adsorbed on the catalytic surface, an activated complex is formed.
This activated complex decomposes to give the product.
Steps involved in heterogeneous catalysis.

1. Reactant molecules diffuse from bulk to the catalyst surface.
2. Reactant molecules are adsorbed on the surface of the catalyst.
3. Adsorbed reactant molecules are activated to form activated complex which is decomposed to form the products.
4. Product molecules are desorbed.
5. Product molecules diffuse away from the surface of the catalyst.

Part – II – Additional Questions

Question 1.
a) Bulk phenomenon
b) Surface phenomenon
c) Both (a) and (b)
d) None of the above
b) Surface phenomenon

Question 2.
Absorption is a
a) Bulk phenomenon
b) Surface phenomenon
c) Both (a) and (b)
d) None of the above
a) Bulk phenomenon

Question 3.
Which among the following is an adsorbent?
a) N2
b) SO2
c) Ni
d) NH3
c) Ni

Question 4.
In adsorption, if the concentration of a substance in the interface is high, then it is called?
a) Desorption
d) Absorption

Question 5.
a) Spontaneous
b) Non-spontaneous
c) Slow
d) Bulk phenomenon
a) Spontaneous

Question 6.
a) Increase in entropy
b) Increase in free energy
c) Decrease in free energy
d) No change in entropy
c) Decrease in free energy

Question 7.
a) Vanderwaal’s force
b) Dipole-dipole interaction
c) Dispersion forces
d) All the above
d) All the above

Question 8.
Total amount of the gas adsorbed increases as the ……………. of the adsorbent increases.
a) Volume
b) Density
c) Surface area
d) Surface tension
c) Surface area

Question 9.
a) lower
b) higher
c) zero
d) none of the above
b) higher

Question 10.
Which among the following gas is adsorbed slowly?
a) SO2
b) NH3
c) N2
d) CO2
c) N2
Reason: Critical temperature of N2 is low hence adsorbed slowly.

Question 11.
a) Exothermic
b) Endothermic
c) Both (a) and (b)
d) None of the above
a) Exothermic

Question 12.
Multi molecular layers are formed in
a) Absorption
b) Physisorption
c) Chemisorption
d) None of the above
b) Physisorption

Question 13.
The rate constant of a reaction at temperature 200K is 10 times less than the rate constant at 400K. What is the activation energy of the reaction? (R=gas constant)
a) 1842.4R
b) 921.2 R
c) 460.6 R
d) 230.3 R
b) 921.2 R

Question 14.
a) Pressure
b) Temperature
c) Volume
d) Mass
b) Temperature

Question 15.
In physical adsorption isobar x /m, …………………………. with increase in temperature.
a) Increases
b)Decreases
c) First increases then decreases
d) Does not change
b) Decreases

Question 16.
In chemisorption isobar x /m …………….. with increase in temperature.
a) Increases
b)Decreases
c) First increases then decreases
d) Does not change
c) First increases then decreases

Question 17.
Which of the following is not an equation for Freundlich isotherm?

d

Question 18.
Sugar prepared from molasses in decolourised by adding.
a) Silica gel
b) Permutit
c) Animal Charcoal
d) Activated charcoal
c) Animal Charcoal

Question 19.
Which of the following is not an application of adsorption?
a) Heterogeneous catalysis
c) Froth floatation process
d) Softening of water by boiling
d) Softening of water by boiling

Question 20.
The change of W/O emulsion into O/W emulsion is called …………..
a) Coagulation
b) Emulsification
c) Decomposition
d) Invension of phase
d) Invension of phase

Question 21.
2SO2 + O2 + [NO] → 2SO3 + [NO] is an example for
a) Positive catalysis
b) Negative catalysis
c) Homogeneous catalysis
d) Both (a) and (c)
d) Both (a) and (c)

Question 22.
Which is not a heterogeneous catalysis?
a) Contact process
b) Haber’s process
c) Ester hydrolysis
d) Ostwald’s process
c) Ester hydrolysis

Question 23.
Intermediate compound formation theory explains.
a) Homogeneous catalysis
b) Heterogeneous catalysis
c) Autocatalysis
d) Negative catalysis
a) Homogeneous catalysis

Question 24.
In intermediate compound formation, the intermediate complex formed has
a) More activation energy than uncatalysed complex
b) Less activation energy than uncatalysed complex
c) Less kinetic energy than the reactants
d) Less kinetic energy than the products
b) Less activation energy than uncatalysed complex

Question 25.
a) Homogeneous catalysis
b) Heterogeneous catalysis
c) Autocatalysis
d) Negative catalysis
b) Heterogeneous catalysis

Question 26.
The catalytic activity of a catalyst is increased by a promoter by
a) Increasing the number of active centres
b) Decreasing the number of active centres.
c) Blocking the number of active centres
d) Desorbing the active centres
a) Increasing the number of active centres

Question 27.
Enzymes are often present as
a) Crystalloids
b) Suspension
c) Colloids
d) True solutions
c) Colloids

Question 28.
In the conversion of 1 – chloro octane into 1 – cyano octane, tetra alkyl ammonium cation acts as a
a) Enzyme catalyst
b) Phase transfer catalyst
c) Zeolite catalyst
d) Nano catalyst
b) Phase transfer catalyst

Question 29.
Which of the following is incorrect
a) Enzymes can be inhibited (poisoned)
b) Calalytic activity of enzymes is decreased by coenzvmes.
c) Enzyme catalysis is highly specific in nature
d) the rate of Enzyme catalysed reactions varies with the pH of the system.
b) Calalytic activity of enzymes is decreased by coenzymes.

Question 30.
Nano catalysts can act as
a) Homogeneous catalysts
b) Heterogeneous catalysts
c) Phase transfer catalysts
d) Both (a) and (b)
d) Both (a) and (b)

Question 31.
Size of colloidal particle is
a) 1 – 200 Å
b) 1 – 200 nm
c) 1 – 200 pm
d) 1 – 200 pm
b) 1 – 200 nm

Question 32.
In hydrosols the dispersion medium is
a) Benzene
b) Alcohol
c) Water
d) Ether
c) Water

Question 33.
In lyophillic colloids which is true?
a) Definite attractive force exists between the dispersion medium and dispersed phase
b) More stable
c) Reversible sols
d) All the above
d) All the above

Question 34.
In lyophobic colloids which is not true?
a) No attractive force exists between the dispersion medium and dispersed phase
b) Less stable
c) Can be produced again
c) Can be produced again

Question 35.
Which among the following is a liquid aerosol?
a) Smoke
b) Fog
c) Shaving cream
d) Froth
b) Fog

Question 36.
Which one of the following is negatively charged colloid?
a) arsenic sulphide
b) Ferric hydroxide
c) Haemoglobin
d) Basic dyes
a) arsenic sulphide

Question 37.
Butter is a colloid of
In butter the dispersed phase and the
dispersion medium are respectively [222EE3
a) Solid, gas
b) Liquid, solid
c) Solid, liquid
d) Gas, solid
c) Solid, liquid

Question 38.
In butter the dispersed phase and the dispersion medium are respectively_______
a) Solid in liquid
b) Liquid in solid
c) Liquid in liquid
d) Liquid in gas
b) Liquid in solid

Question 39.
Colloidal graphite can be prepared by
a) Peptisation
b) Mechanical dispersion
c) Ultrasonic dispersion
d) Double decomposition
b) Mechanical dispersion

Question 40.
Electro dispersion method is used to prepare the colloidal solution of
a) Copper
b) Silver
c) Gold
d) All the above
d) All the above

Question 40.
Arsenic sulphide sol is prepared by the reaction. AS2O3 + 3H2S → As2S3 + 3H2O. This method is known as
a) Hydrolysis
b) Double decomposition
c) Oxidation
d) Reduction
b) Double decomposition

Question 42.
Conversion of a colloid into a precipitate is known as
a) Peptisation
b) Dialysis
c) Coagulation
d) Electrophoresis
c) Coagulation

Question 43.
Conversion of a precipitate into a colloid is known as
a) Peptisation
b) Dialysis
c) Coagulation
d) Electrophoresis
a) Peptisation

Question 43.
The removal of electrolytic impurities from a colloidal solution is known as
a) Peptisation
b) Dialysis
c) Coagulation
d) Electrophoresis
b) Dialysis

Question 44.
The movement of dispersed phase under the influence of electric current is known as
a) Electro osmosis
b) Electrophoresis
b) Dialysis
d) Electrophoresis
b) Dialysis

Question 45.
The movement of dispersed phase under the influence of electric current is known as
a) Electro osmosis
b) Electrophoresis
c) Electrodialysis
d) Ultra filteration
b) Electrophoresis

Question 46.
The movement of dispersion medium under the influence of electric current is known as
a) Electro osmosis
b) Electrophoresis
c) Electrodialysis
d) Ultra filteration
a) Electro osmosis

Question 47.
In ultra filteration, ultrafilters are made by using
a) Collodion
b) Cellophane
c) Both (a) and (b)
d) None of the above
c) Both (a) & (b)

Question 48.
Collodion is 4% solution of ……………… in a mixture of alcohol and water.
a) Cellulose acetate
c) Chioro cellulose
b) Cellulose sulphate
cl) Nitrocellulose
d) Nitrocellulose

Question 49.
Blue colour of the sky. in nature is due to
a) Browniart movement
b) Tyndall effect
c) Both (a) and (b)
d) None of thé above
b) Tyndall effect

Question 50.
Scattering of light by colloidal particles is known as
a) Brownian movement
b) Tyndall effect :
c) Electrophoresis
d) Electro osmosis
b) Tyndall effect

II. Match the following

Question 1.

 I II i) Auto Catalyst Hydrated alumino zilicates ii) Nano catalyst Al2O3 in Haber’s process iii) Zeolite catalyst Fe / Pd iv) Catalytic poison Urease v) Promoter Anhydrous AlCl3 vi) Enzyme catalyst As2O3 in contact process decomposition of arsine.

i) Arsenic in the decomposition of arsine
i) Fe/Pd
ii) Hydrated aluminosilicates
iii) As2O3 in contact process
iv) Al2O3 in Haber’s process
v) Urease

Question 2.

 Process Catalyst i) Haber’s process Cupric chloride ii) Contact process Nitric oxide iii) Lead chamber process Ferric oxide iv) Deacon’s process Iron v) Bosch’s process Platinum

i) Iron
ii) Platinum
iii) Nitric oxide
iv) Cupric chloride
v) Ferric oxide

Question 3.

 Column A Column B i) Solid aerosol Paints ii) Emulsion Bread iii) Sol Dust iv) Solid foam Alloys v) Solid sol Milk

i) Dust
ii) Milk
iii) Paints
v) Alloys

III. Assertion and Reasoning

Question 1.
Assertion (A) : Physical adsorption occurs at low temperatures.
Reason (R) : The forces of attraction between the adsorbent and adsorbate are weak and heat of adsorption is low
a) Both A and R are correct, R explains A
b) Both A and R are correct, R does not explain A
c) A is correct but R is wrong
d) A is wrong but R is correct.
a) Both A and R are correct, R explains A

Question 2.
Assertion (A) : In the reaction CH3COOC2H5 + H20 -> CH3COOH + C2H5OH is an example for autocatalysis.
Reason (R) : One of the product ethanol acts as a catalyst.
a) Both A and R are correct, R explains A
b) Both A and R are correct, R does not explain A
c) A is correct but R is wrong
d) A is wrong but R is correct.
c) A is correct but R is wrong.
Correct Reason: One of the product acetic acid acts as a catalyst.

Question 3.
Assertion (A) : 1- Chioro octane is converted into 1 – Cyano octane in I or 2 hours by reacting with sodium cyanide in presence of tetra alkyl ammonium chloride.
Reason (R) : The tetra alkyl ammonium cation transports CN from the aqueous phase to the
organic phase using its hydrophilic end.
a) Both A and R are correct, R explains A
h) Both A and R are correct, R does do not explain A
c) A is correct hut R is wrong
d) A is wrong but R is correct.
a) Both A and R are correct, R explains A

Question 4.
Assertion (A): Measurements of osmotic pressure is used to find the molecular weight of colloidal particle.
Reason (R): Colloidal solutions show the kinetic property,
a) Both A and R are correct, R explains A
b) Both A and R are correct, R does not explain A
c) A is correct but R is wrong
d) A is wrong but R is correct.
b) Both A and R are correct, R does not explain A Correct Reason: Colloidal solutions show colligative properties.

IV. Choose the correct statement

Question 1.
i) Chemisorption is instantaneous
ii) Chemisorption first increases and then decreases with temperature
iii) In chemisorption the heat of adsorption is high
iv) Chemisorption is independent of the surface area of the adsorbent
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (i) & (iv)
b) (ii) & (iii)
Correct statement:
Chemisorption is slow,
Chemisorption depends on the surface area of the adsorbent.

Question 2.
i) A catalyst can initiate a reaction
ii) A solid catalyst will be more effective if it is taken in bulk
A catalyst does not affect the position of equilibrium and the value of the equilibrium constant
A catalyst is highly effective at a particular temperature called optimum temperature,
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (i) & (iv)
c) (iii) & (iv)

Correct statement:
A catalyst cannot initiate a reaction,
A solid catalyst will be more effective if it is taken in a finely divided form.

Question 3.
i) When light passes through colloidal solution it is scattered in all directions.
ii) When a colloidal solution is observed through ultramicroscope, they showed a random, zigzag, ceaseless motion.
iii) Haemoglobin is a negatively charged colloid
iv) A sol is not electrically neutral.
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (i) & (iv)
a) (i) & (ii)

Correct statement: iii) Haemoglobin is a positively charged colloid, iv) A sol is electrically neutral

Question 4.
i) The flocculation and setting down of the sol particles is called coagulation.
ii) The higher the flocculation value greater will be the precipitation.
iii) Lyophilic sols are precipitated readily even with small amount of electrolytes.
iv) When boiled due to increased collisions, the sol particles combine and settle down.
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (i) & (iv)
d) (i) & (iv)

Correct statement:
ii) The smaller the flocculation value greater will be the precipitation,
iii) Lyophobic sols are precipitated readily even with small amount of electrolytes

V. Choose the incorrect statement

Question 1.
i) Physisorption decreases with an increase in pressure
ii) Physisorption decreases with an increase in temperature
iii) Activation energy of physisorption is significant
iv) No transfer of electrons occur in physisorption
a) (i) & (ii)
b) (ii) & (iii)
c) (i) & (iii)
d) (iii) & (iv)
c) (i) & (iii)

Correct statement:
i) Physisorption increases with increase in pressure,
iii) Activation energy of physisorption is insignificant.

Question 2.
i) Enzyme catalysis is highly specific in nature
ii) The rate of enzyme catalysed reactions does not vary with pH of the system
iii) Catalytic activity of enzymes is decreased by coenzymes.
iv) Enzyme catalysed reaction has maximum rate at optimum temperature.
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (i) & (iv)
b) (ii) & (iii)

Correct statement:
ii) The rate of enzyme catalysed reactions varies with pH of the system,
iii) Catalytic activity of enzymes is increased by coenzymes.

Question 3.
i) In zeolites the active sites namely protons are lying inside their pores.
ii) Reactions occur only outside the pores of zeolites.
iii) Bulkier reactant molecules are prevented from reaching the active sites within- the zeolite crystal.
iv) If the transition state of a reaction is large compared to the pore size of the zeolite, then product will be formed.
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (ii) & (iv)
d) (ii) & (iv)
Correct statement:
ii) Reactions occur only inside the pores of zeolites,
iv) If the transition state of a reaction is large compared to the pore size of the zeolite, then no product will be formed.

Question 4.
i) Colloidal solutions are heterogeneous in nature having two distinct phases.
ii) Colloidal solutions are unstable and they are affected by gravity.
iii) When the colloidal solution is dilute coagulation occurs.
iv) Unlike true solution, colloids diffuse less readily through membranes.
a) (i) & (ii)
b) (ii) & (iii)
c) (iii) & (iv)
d) (i) & (iv)
b) (ii) & (iii)
Correct statement:
ii) Colloidal solutions are quite stable and they are not affected by gravity,
iii) When the colloidal solution is dilute coagulation does not occur

VI. Two Mark Questions

Question 1.

• Adsorption is a phenomenon of concentration of a substance on the surface of a liquid or gas.
• Adsorption is a surface phenomenon.

Question 2.
What is known as interface?
The surface of separation of the two phases where the concentration of adsorbed molecule is high is known as the interface.

Question 3.
If the concentration of a substance in the interface is high in an adsorption, then it is called positive adsorption. If it is less, then it is called negative adsorption.

Question 4.
What is desorption?
The process of removing an adsorbed substance from the surface is called desorption.

Question 5.
Absorbent is the material on which adsorption takes place.

Question 6.

• Gaseous molecules like He, Ne, O2, SO2 and NH3
• Solutions of NaCl, KCl

Question 7.
Silica Gel
Metals like Ni, Cu, Pi. Ag and Pd
Certain colloids.

Question 8.
What are the limitations of Freundlich isotherm?

• The equation is purely empirical
• Valid over a limited pressure range.
• Constants k and n values vary with temperature and for this no theoretical explanations were given.

Question 9.
How is adsorption principle used in the softening of hard water?

• Permutit adsorbs Ca2+ and Mg2+ ions present in hard water on its surface.
• An ion exchange occurs on its surface. Na2Al2Si4O12 + CaCl2 → CaAl2 Si4 O12 + 2NaCl
• Exhausted permutit is regenerated by adding a solution of common salt.
CaAl2 Si4 O12 + 2NaCl → Na2Al2Si4O12 + CaCl2

Question 10.
How is ion exchange resins work on the principle of adsorption in demineralising water?

• The process is carried out by passing water through two columns of cation and anion exchange resins.
• Cation exchange:
• Anion exchange:

Question 11.
Define a catalyst.
A catalyst is defined as a substance which alters the rate of chemical reaction without itself undergoing chemical change.

Question 12.
What is meant by positive catalysis and negative catalysis?

• In positive catalysis the rate of a reaction is increased by the presence of a catalyst.
• In negative catalysis the rate of a reaction is decreased by the presence of a catalyst.

Question 13.
What are promoters?

• The substance which increases the activity of a catalyst in a reaction is called promoter.
• (Eg-) In Haber’s process of synthesis of NH3, MO is the promoter of Fe catalyst.

Question 14.
What are the limitations of intermediate compound formation theory.

• Fails to explain the action of catalytic poison and promoters.
• Unable to explain the mechanism of heterogeneous catalysis.

Question 15.
What are active centres?

• Surface of a catalyst is not smooth.
• It bears steps, cracks and corners.
• The atoms on such locations are coordinatively unsaturated.
• So they have much residual force of attraction.
• Such sites are called active centres.

Question 16.
What is a colloidal solution?
When the diameter of the particles of a substance dispersed in a solvent ranges from 1 – 200 nm, the system is called a colloidal solution.

Question 17.
What is meant by dispersion medium and dispersed phase?
In a colloid, the substance present in a larger amount is called dispersion medium and the substance present in less amount is called the dispersed phase.

Question 18.
What is the flocculation value?
The precipitation power of electrolyte is determined by finding the minimum concentration(millimoles/lit ) required to cause precipitation of a sol in 2 hours. This value is called flocculation value.
The smaller the flocculation value greater will be precipitation.

Question 19.
Name the dispersion medium present in hydrosol, alcosol and benzosol.

 Colloid Dispersion Medium i Hydrosol Water ii Alcosol Alcohol iii Benzosol Benzene

Question 20.
How is a colloid prepared by exchange of solvent ?

• Colloidal solution of phosphorous or sulphur is obtained by preparing the solutions in alcohol and pouring them into water.
• As they are insoluble in water, they form colloidal solution P in alcohol + water —> P Sol

Question 21.
What is Tyndall effect?
The scattering of light by colloidal particles is called Tyndall effect.

Qu

estion 22.
What is Brownian movement?

• The random, zigzag, ceaseless motion of colloidal particles in dispersion medium is known as Brownian movement.
• This is due to the continuous bombardment of dispersed phase bv the molecules of dispersion medium.

Question 23.
What is the significance of Brownian movement ?

• To confirm kinetic theory which considers the ceaseless rapid movement of molecules that increases with increase in temperature.
• To understand the stability of colloids.
• As the particles are in continuous rapid movement they do not come close and hence not get condensed. That is Brownian movement does not allow the particles to be acted by force of gravity.

Question 24.
Define ‘gold number’

• 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% NaCl solution.
• Smaller the gold number greater the protective power.

Question 25.
What are emulsions?
Write their types.

• Emulsions are colloidal solution in which a liquid is dispersed in another liquid.
• Two types of emulsions are
(i) Oil in water (O/W)
(ii) Water in oil (W/ O)

Question 26.
What is emulsification?
The process of preparation of emulsion by the dispersal of one liquid in another liquid is called emulsification.

Question 27.
What is de emulsification?
The process of separation of an emulsion into two separate layers is called de emulsification.

Question 28.
Write the uses of colloids in medicine?

• Antibodies such as penicillin and streptomycin are produced in colloidal form for suitable injections.
• Colloidal gold and colloidal calcium are used as tonics.
• Milk of magnesia is used for stomach troubles.
• Silver sol protected by gelatine known as Argyrol is used as eye lotion.

Question 29.
Mention the shapes of the following colloidal particles,
i) AS2S3
ii) Blue gold sol
iii) Tungstic acid sol
i) AS2S3 -Spherical
ii) Blue gold sol – Disc or plate like
iii) Tungstic acid sol – Rod like

VII. Three Mark Questions

Question 1.

• Adsorption can occur in all interfacial surfaces (ie) between gas-solid, liquid-solid, liquid-liquid, solid-solid, gas-liquid
• Adsorption is always accompanied by decrease in free energy. When ΔG = 0, the equilibrium is attained.
• Adsorption is a spontaneous process.
• Adsorption is accompanied by decrease in randomness (ie) decrease in entropy.
• Adsorption is a quick process.

Question 2.
Write a note on Freundlich isotherm.

According to Freundlich x/m = kp1/n
m = mass of adsorbent in gram
p = pressure
k, n = constants, value of n is always less than unity.

This equation is applicable for adsorption of gases on solid surfaces.
For adsorption in solutions of concentration C, the equation is x/m = kC1/n
These equations quantitatively predict the effect of pressure or concentration on the adsorption of gases or liquids at constant temperature
Taking log

Question 3.
Write a note on (i) auto catalysis , (ii) negative catalysis ?
Auto catalysis:
When one of the products formed acts as a catalyst to the reaction it is called as auto catalysis and that product is-called as auto catalyst.
(Eg.) CH3COOC2H5 + H2O → CH3COOH + C2 + C2H5OH
Acetic acid acts as the auto catalyst.

Negative catalysis:
When certain substances decreases the rate of the reaction, it is called negative catalysis and the substance is called negative catalyst.
(Eg.) 2H2O2 → 2H2O + O2
Glycerol acts as a negative catalyst in the above reaction.

Question 4.
What is the role of adsorption in the heterogeneous catalysis.
In heterogenous catalysis, the reactants are converted into products only when the reactants are adsorbed on the catalyst surface to form an activated complex which subsequently decomposes to give the product. Hence the role of adsorption is to form activated complex.

Question 5.
Give some examples for enzyme catalysis.

Question 6.
Write a note on nano catalysis.

• Metallic nano particles, metal oxides are used as catalysts.
• Nano catalysts can act as both homogeneous as well as heterogeneous catalysts.
• Like homogeneous catalysts they give 100% selective transformations and excellent yield and show extremely high activity.
• Like heterogeneous catalysts, they can be recovered and recycled.
• Nano catalysts are actually soluble heterogeneous catalysts.

Question 7.
How can you identify the two types of emulsion.

 Test Oil in water (O/W) emulsion (aqueous emulsion) Water in oil (W/O) emulsion (oily emulsion) i) Dye test: A small amount of dve soluble in oil is added. Does not take up the colour Takes up the colour. ii) Viscosity test Lower viscosity Higher viscosity iii) Conductivity test Higher conductivity Lower conductivity. iv) Spreading test Spread less readily on an only surface. Spread readily on an only surface.

Question 8.
Name some of the de emulsification techniques.

• Distilling one component.
• Adding an electrolyte to destroy the charge. Destroying the emulsifier using chemical methods.
• Using solvent extraction to remove one component.
• By freezing one of the components.
• By applying centrifugal force.
• Adding dehydrating agents for water in oil (W/O) type.
• Using ultrasonic waves.
• Heating at high pressure.

VIII. Five Mark Questions

Question 1.
What are the general characteristics of catalysts.

• Only a small quantity of catalyst is needed for a reaction.
• There may be some physical changes, but the catalyst remains unchanged’ in mass and its chemical composition.
• A catalyst cannot initiate a reaction, only it speeds up a slow reaction.
• A solid catalyst is more effective in a finely divided form.
• Catalysts are specific in nature.
• A catalyst does not affect the position of equilibrium and the value of equilibrium constant but helps the quick attainment of equilibrium.
• A catalyst is highly effective at a particular temperature called as optimum temperature.
• Presence of a catalyst does not change the nature of products.

Question 2.
What are the special characteristics shown by enzyme catalysed reaction?
Effective and efficient conversion An enzyme may transform a million molecules of reactant in a minute. (Eg.) 2H2O2 → 2H2O + O2

Enzyme catalysis has maximum rate at optimum temperature. The temperature at which the enzymic activity is high or maximum is called as optimum temperature.
Enzymes involved in human body have an optimum temperature 37°C.
The rate of enzyme catalysis varies with pH of the system. The pH at which the rate is maximum is called the optimum pH.
Enzymes can be inhibited or poisoned. Penicillin inhibits the action of bacteria and used for curing diseases like pneumonia, dysentery, cholera.
A small non protein (vitamin) called a coenzyme promotes the catalytic activity of enzyme.

Question 3.
Explain phase transfer catalysis.

• If the reactants of a reaction are present in two different solvents which are immiscible, the reaction between them is very slow.
• As the solvents form separate phases, the reactants have to migrate across the boundary to react.
• But migration across the boundary is not easy.
• For such a situation a third solvent miscible with both is added.
• So the phase boundary is eliminated and the reactants mix freely and react fast.
• But for large scale production of any product, use of a third solvent is not convenient as it may be expensive.
• Phase transfer catalysis gives a simple solution for such problems as it avoids the use of solvents.
• Phase transfer catalyst facilitate the transport of a reactant in one solvent to the other solvent where the second reactant is present.
• As the reactants are brought together, they rapidly react and form the product.
R – Cl + NaCN → R-CN + NaCl
Organic phase aqueous phase Organic phase aqueous phase
• RC1 = 1 – chloro octane, RCN = 1 – cyano octane
1- cyano octane is not obtained by directly heating organic phase, 1 – chloro octane ^ with aqueous phase sodium cyanide for^ ’ several days.
• If a small amount of tetra alkyl ammonium chloride is added, 1 – cyano octane occurs in about 100% yield after 1 or 2 hours.
• In this reaction, the tetra alkyl ammonium cation containing hydrophobic and hydrophilic ends, transports CN from the aqueous phase to the organic phase using its hydrophilic end.
• Both in organic phase Organic phase
It moves to aqueous phase, releases Cl— again picks up CN and transports it.
• So phase transfer catalyst speeds up the reaction by transporting one reactant from one phase to another.

Question 4.
Explain dispersion methods of preparing colloids

Mechanical Dispersion:
The solid is ground to colloidal dimension using a colloid mill consists of two metal plates rotating in opposite direction at very high speed of nearlv 7000 revolution / minute.
Required colloidal si/.e is obtained bv adjusting the distance between the two plates.
(Eg.) Colloids of ink and graphite.

ii) Electro Dispersion :
An electric arc is struck between electrodes dispersed in water surrounded by ice.
When a current of l amp/100 v is passed, an arc produced forms vapours of metal which immediate!) condense to form colloidal solution
Alkali hvdroxide is added as an stabilising agent.
(Eg.) Colloids of metals like copper, silver, gold, platinum
Svedberg modified this method for the prepartion of non-aqueous inflammable liquids like pentane, ether and benzene using high frequency alternating current which prevents the decomposition of the liquid.

iii) Ultrasonic Dispersion:
Sound wraves of frequency more than 20 KHz transform coarse suspension to colloids. Claus obtained mercury sol by subjecting mercury to sufficiently high frequency ultrasonic vibrations.
Ultrasonic vibrations produced by generator spread through the oil and transfer the vibration to the vessel with mercury in water.

iv) Peptisation:
Conversion of a precipitate into colloid by the addition of electrolyte is called peptisation.
Added electrolyte is called peptising or dispersing agent.

Question 5.
Explain condensation methods of preparing colloids.
i) Oxidation:
Sols of non metals are prepared by this method
HIO3 + 5HI → 3H2O + I2 (sol)

ii) Reduction:
Gold sol is prepared by reducing auric chloride using organic reagent formaldehyde.
2AUCl3 + 3HCHO + 3H2 → 2Au (sol) + 6HCl + 3HCOOH

iii) Hydrolysis :
Sols of metal hydroxides are prepared by this method.
FeCl3 + 3H2O → Fe(OH)3 + 3HCl

Double decomposition:
Water insoluble sols are prepared by this method. Yellow coloured arsenic sulphide sol is prepared by passing hydrogen sulphide gas through arsenic oxide.
AS2O3+ 3H2S → AS2S3 + 3H2O

vi) Decomposition:

• When a few drops of an acid is added to sodium thio sulphate, it decomposes to form insoluble free sulphur.
• Insoluble free sulphur accumulates into small clusters which impart various colours blue, yellow and even red to the system.
• This colour change is due to their growth within the size of colloidal dimensions.

Question 6.
Explain various methods of purification of colloids.

Dialysis:

• Colloidal solution is taken in a bag made up of semipermeable membrane.
• It is suspended in a trough of flowing water.
• Electrolytes diffuse out of the membrane and they are carried away by water.

Electro dialysis :

• The presence of electric field increases the speed of removal of electrolytes from colloidal solution.
• Colloidal solution with electrolytic impurity is placed between two dialysing membranes enclosed into two compartments filled with water.
• When current is passed, the impurities pass into water compartment and get removed periodically.
• This process is faster than dialysis, as the rate of diffusion of electrolytes is increased by the application of electricity.

iii) Ultra filtration:

• The pores of ordinary filter papers allow the passage of colloidal particles.
• In ultra filtration the membranes are made by using colloidion, cellophane or visiking.
• When a colloidal solution is filtered using such a filter, colloidial particles are separated on the filter and the impurities are removed as washings.
• This process is quickened by the application of pressure.
• Collodion is 4% solution of nitrocellulose in a mixture of alcohol and water.
• This method of separation of sol particles from electrolyte by filtration through an ultrafilter is called ultrafiltration.

Question 7.
Write a note on Helmholtz double layer.

• The surface of colloidal particle adsorbs one type of ion due to preferential adsorption
• This layer attracts the oppositely charged ions in the medium.
• Hence at the boundary separating the two, electrical double layers are set up.
• This is called as Helmholtz electrical double layer.
• As the particles nearby are having similar charges, they cannot come close and condense.
• This explains the stability of a colloid.

Question 8.
Write a note on electrophoresis.