IISER Chemistry - Adsorption and Colloids
Exam Duration: 45 Mins Total Questions : 30
Colloidal solutions of gold prepared by different methods are of different colours because of
- (a)
different diameters of colloidal gold particles
- (b)
Variable valency of gold
- (c)
different concentration of gold particles
- (d)
impurities produced by different methods
The charge on AS2S3 sol. is due to the adsorbed
- (a)
H+
- (b)
OH-
- (c)
O2-
- (d)
S2-
The amount of NaCl, MgCl2 and AlCl3 required to coagulate a fixed amount of As2S3 sol. wil very in the order of
- (a)
NaCl < MgCl2 < AlCl3
- (b)
NaCl > MgCl2 > AlCl3
- (c)
NaCl < MgCl2 > AlCl3
- (d)
NaCl > MgCl2 < AlCl3
Which one of the following statements is wriong about adsorption?
- (a)
It is a selective and secific process
- (b)
It is a reversible process
- (c)
An increase in the gaseous adsorbate causes increase in adsorption. However, at high pressure, the adsorption becomes constant
- (d)
It is an endothermic process
An emulsifier is an agent which
- (a)
accelerates the dispersion
- (b)
homogenises an emulsion
- (c)
stabilises an emulsion
- (d)
aids the flocculation of an emulsion
Positively charged and negatively charged sols can be distinguished by
- (a)
the addition of 1 : 1 electrolyte
- (b)
the addition of AlPO4
- (c)
the addition of MgSO4
- (d)
electrophoresis
Which one of the following can form a +ve as well as a -ve colloid?
- (a)
AgCl
- (b)
Fe(OH)3
- (c)
As2S3
- (d)
AlPO4
Which one of the following is a lyophillic colloid?
- (a)
milk
- (b)
gum
- (c)
fog
- (d)
blood
The stability of lyophilic colloids is due to
- (a)
charge on their particles
- (b)
a layerof medium of dispersion on their particles
- (c)
the smaller size of their particles
- (d)
the large size of their particles
According to Langmuir adsorption isotherm, the amount of gasadsorbed at very high pressures
- (a)
reaches a constant limiting value
- (b)
goes on increasing with pressure
- (c)
goes on decreasing with pressure
- (d)
increases first and decreases later with pressure
Which one of the following catalysts selectively changes n-heptane to toluene?
- (a)
Pt catalysts
- (b)
bismuth molybdate catalysts
- (c)
V2O5 catalysts
- (d)
NONE OF THE ABOVE
The path of the beam light is visible because
- (a)
carbondioxide in the smoke absorbs light
- (b)
carbondioxide in the smoke scatters light
- (c)
colloidal particles in the smoke absorbs light
- (d)
colloidal particles in the smoke scatters light
Point out the false satement :
- (a)
Brownian movement and Tyndall effece is shown by colloidal systems.
- (b)
Gold number is a measure of the protective power of a lyophillic colloid.
- (c)
The colloidal solution of a liquid in liquid is called gel.
- (d)
Hardy-Schulze rule is related with coagulation.
Which one of the following sols is hydrophobic?
- (a)
gum
- (b)
gelatin
- (c)
starch
- (d)
sulphur
For the styrene foam, the dispersed phase and dispersion medium are ............. and ................ respectively.
- (a)
gas, gas
- (b)
solid, gas
- (c)
gas, solid
- (d)
None of the above
Which of the following is a best example of associated colloid?
- (a)
Protein in water
- (b)
Soap in water above CMC
- (c)
Rubber in benzene
- (d)
FeCl3 in H2O
Which of the following is used to prepare colloidal solution of gold?
- (a)
Colloidal mill
- (b)
Double decomposition method
- (c)
Bredig's method
- (d)
Peptisation
Which of the following electrolytes will have maximum coagulating value for AgI/Ag+ sol?
- (a)
Na2S
- (b)
Na3PO4
- (c)
Na2SO4
- (d)
NaCl
Amongst the electrolytes Na2SO4, CaCl2, Al2(SO4)3 and NH4Cl, the most effective coagulating agent for Sb2S3 sol is.
- (a)
Na2SO4
- (b)
CaCl2
- (c)
Al2(SO4)3
- (d)
NH4Cl
Gold number of protective colloids A, B, C and D are 0.50, 0.01, 0.10 and 0.005 respectively. The correct order of their protective power is
- (a)
D < A < C < B
- (b)
C < B < D < A
- (c)
A < C < B < D
- (d)
B < D < A < C
The volume of a colloidal particle, Vc as compared to the volume of a solute particle in a true solution Vs , could be
- (a)
\(\frac{V_c}{V_s}=10^3\)
- (b)
\(\frac{V_c}{V_s}=10^{-3}\)
- (c)
\(\frac{V_c}{V_s}=10^{23}\)
- (d)
\(\frac{V_c}{V_s}=1\)
Which of the following is an example of absorption?
- (a)
Water on silica gel
- (b)
Water on CaCl2
- (c)
H2 on finely divided Ni
- (d)
O2 on metal surface
Gas mask is prepared on the basis of adsorption because
- (a)
it causes adsorption of poisonous gases on activated charcoal
- (b)
it causes absorption of gaseous particles
- (c)
it increases oxygen molecule around the atmosphere by decreasing concentration of poisonous gases
- (d)
Both (a) and (c)
In physisorption, the molecules o adsorbate held to the adsorbent by
- (a)
chemical forces
- (b)
ionic forces
- (c)
van der Waals' forces
- (d)
None of the above
Which of the following is a false characteristic for physisorption?
- (a)
Adsorption on solid is a reversible process
- (b)
Adsorption is a spontaneous process
- (c)
Both enthalpy and Gibbs free energy is negative
- (d)
Adsorption increases with increase in temperature
Physisorption is exothermic in nature because
- (a)
\(\Delta H<0\)
- (b)
\(\Delta H>0\)
- (c)
\(\Delta H=0\)
- (d)
None of these
Heat of adsorption for chemical adsorption falls under the range of
- (a)
20-80 kcal/mol
- (b)
5-10 kcal/mol
- (c)
100-200 kcal/mol
- (d)
0-5 kcal/mol
Which of the following is true for critical temperature(Tc) and extent of adsorption?
- (a)
Extent of adsorption is larger for higher value of Tc
- (b)
Extent of adsorption is lower for higher value of Tc
- (c)
There is no relation between extent of adsorption and Tc
- (d)
None of the above
Point out the correct statement for chemisorption.
- (a)
It is exothermic and monolayered
- (b)
It is endothermic and monolayered
- (c)
It has enthalpy of adsorption in between 0-5kal mol-1
- (d)
All of the above
In Langmuir's model of adsorption of a gas on a solid surface,
- (a)
the rate of dissociation o adsorbed molecules from the surface does not depend on the surface covered
- (b)
the adsorption at a single site on the surface may involve multiple molecules at the same time
- (c)
the mass of gas striking a given area of surface is proportional to the pressure of the gas.
- (d)
the mass of gas striking a given area of surface is independent of the pressure of the gas.
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