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71.
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.
Answer :
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 diluted with any amount of the dispersion medium. On the other hand, the dispersed liquid when mixed, forms a separate layer.
72.
According to Freundlich adsorption isotherm which of the following is correct?
A
$$\frac{x}{m} \propto {p^ \circ }$$
B
$$\frac{x}{m} \propto {p^1}$$
C
$$\frac{x}{m} \propto {p^{\frac{1}{n}}}$$
D
All the above are correct for different ranges of pressure
Answer :
All the above are correct for different ranges of pressure
The Freundlich adsorption isotherm is mathematically represented as $$\frac{x}{m} = k{P^{\frac{1}{n}}}$$
$$\eqalign{
& {\text{at high pressure}}\,\,\frac{1}{n} = 0.\,\,{\text{Hence}},\,\,\frac{x}{m} \propto {P^ \circ } \cr
& {\text{at low pressure}}\,\,\frac{1}{n} = 1\,\,{\text{Hence}},\,\,\frac{x}{m} \propto P' \cr} $$
73.
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 getting precipitated
Answer :
To coagulate the suspended impurities
The water obtained from natural sources often contains suspended impurities. Alum is added to such water to coagulate the suspended impurities and make water fit for drinking purposes.
74.
Fog is a colloidal solution of
A
Gas in liquid
B
Solid in gas
C
Gas in gas
D
Liquid in gas
Answer :
Liquid in gas
Fog is a colloidal solution of liquid in a gas, in which liquid is the dispersed phase whereas gas is the dispersion medium. Examples of other options are as follows:
Gas in liquid : Shaving cream, soda water, froth
Solid in gas : Dust in air
Gas in gas : Atmospheric air.
75.
When a small quantity of $$FeC{l_3}$$ solution is added to the fresh precipitate of $$Fe{\left( {OH} \right)_3},$$ 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
Answer :
peptization
Peptization involves conversion of freshly prepared precipitate into colloidal particles using a suitable electrolyte.
76.
The combination of two layers of opposite charges around the colloidal particle is called Helmholtz electrical double layer. The potential difference between the fixed layer and the diffused layer of opposite charge is called
A
electrode potential
B
zeta potential
C
adsorption potential
D
diffused potential
Answer :
zeta potential
The first layer of ions is firmly held and is termed as fixed layer while the second layer is mobile or diffused layer according to Helmholtz electrical double layer. The potential difference between fixed and diffused layer is called electrokinetic potential or zeta potential.
77.
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
Answer :
Colloidal solution of palladium
In colloidal solution the particles are suspended and are more dispersed than powdered form hence adsorption is maximum.
78.
A colloidal system having a solid substance as a dispersed phase and a liquid as a dispersion medium is classified as ________.
A
solid sol
B
gel
C
emulsion
D
sol
Answer :
sol
Sol is a type of colloid in which solid substance is dispersed phase and liquid is dispersion medium.
79.
Which of the following acts as the best coagulating agent for ferric hydroxide sol ?
A
Potassium ferrocyanide
B
Potassium chloride
C
Potassium oxalate
D
Aluminium chloride
Answer :
Potassium ferrocyanide
The efficiency of coagulation of an electrolyte depends upon its valency. Thus, $${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }}$$ is the best coagulating agent for $$Fe{\left( {OH} \right)_3}$$ sol.
80.
The incorrect statement about physical adsorption is
A
it lacks specificity
B
it is generally reversible
C
porous surfaces are good adsorbent
D
heat of adsorption is quite high
Answer :
heat of adsorption is quite high
Heat of adsorption of physical adsorption is quite low.