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1.
Catalytic poisons act by :
A
making the products chemically inactive.
B
increasing the rate of the backward reaction.
C
chemical combination with any one of the reactants.
D
preferential adsorption on the catalyst surface.
Answer :
preferential adsorption on the catalyst surface.
The catalytic poisons decrease the activity of the catalyst because they are preferentially adsorbed on the surface of catalyst.
2.
When an excess of a very dilute aqueous solution of $$KI$$ is added to a very dilute aqueous solution of silver nitrate, the colloidal particles of silver iodide are associated with which of the following Helmholtz double layer ?
A
$$AgI/A{g^ + }\left| {{I^ - }} \right.$$
B
$$AgI/{K^ + }\left| {NO_3^ - } \right.$$
C
$$AgI/NO_3^ - \left| {A{g^ + }} \right.$$
D
$$AgI/{I^ - }\left| {{K^ + }} \right.$$
Answer :
$$AgI/{I^ - }\left| {{K^ + }} \right.$$
As excess of $$KI$$ has been added, $${I^ - }$$ ions are adsorbed on $$AgI$$ forming a fixed layer ( and giving it a negative charge ). It then attracts the counter ions $$\left( {{K^ + }} \right)$$ from the medium forming a second layer ( diffused layer ).
3.
Among the electrolytes $$N{a_2}S{O_4},CaC{l_2},A{l_2}{\left( {S{O_4}} \right)_3}$$ and $$N{H_4}Cl,$$ the most effective coagulating agent for $$S{b_2}{S_3}$$ sol is
A
$$N{a_2}S{O_4}$$
B
$$CaC{l_2}$$
C
$$A{l_2}{\left( {S{O_4}} \right)_3}$$
D
$$N{H_4}Cl$$
Answer :
$$A{l_2}{\left( {S{O_4}} \right)_3}$$
$$S{b_2}{S_3}$$ is a negatively charged sol. The most effective coagulating agent will be electrolyte with highest positive charge on the cation, $$viz.,A{l_2}{\left( {S{O_4}} \right)_3}.$$ The order is $$A{l^{3 + }} > C{a^{2 + }} > N{a^ + } > NH_4^ + $$
4.
Which of the following is most powerful to coagulate the negative colloid?
A
$$ZnS{O_4}$$
B
$$N{a_3}P{O_4}$$
C
$$AlC{l_3}$$
D
$${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$$
Answer :
$$AlC{l_3}$$
According to Hardy-Schulze rule "The amount of electrolyte required to coagulate a fixed amount of a sol depends upon the sign of charge and valency of the flocculating ion."
Thus, the coagulating power vary in the order.
$$A{l^{3 + }} > Z{n^{2 + }} > N{a^ + }$$
5.
$$100\,mL$$ of $$0.6\,M$$ acetic acid is shaken with $$2\,g$$ activated carbon. The final concentration of the solution after adsorption is $$0.5\,M.$$ What is the
amount of acetic acid adsorbed per gram of carbon?
This is an example of heterogeneous catalysis as the catalyst is present in different phase than that of the reactants.
\[4N{{H}_{3\left( g \right)}}+5{{O}_{2\left( g \right)}}\xrightarrow{P{{t}_{\left( s \right)}}}\] \[4N{{O}_{\left( g \right)}}+6{{H}_{2}}{{O}_{\left( g \right)}}\]
7.
Conditions required for increase in van der Waals' adsorption are respectively
A
high temperature and low pressure
B
high temperature and high pressure
C
low temperature and low pressure
D
low temperature and high pressure
Answer :
low temperature and high pressure
van der Waals' adsorption i.e., physisorption increases at low temperature and high pressure.
8.
The protecting power of lyophilic colloidal sol is expressed in terms of :
A
coagulation value
B
gold number
C
critical miscelle concentration
D
oxidation number
Answer :
gold number
The lyophobic sols are less stable than lyophilic sols. The lyophilic sols are thus used to protect the lyophobic sols. This property of lyophilic sols is known as protective action of lyophilic sols which is represented by gold number.
9.
A plot of $${\text{log}}\left( {\frac{x}{m}} \right)$$ against log $$P$$ for the adsorption of a gas on a solid gives a straight line with slope equal to :
10.
In Langmuir's model of adsorption of a gas on a solid surface
A
the mass of gas striking a given area of surface is proportional to the pressure of the gas
B
the mass of gas striking a given area of surface is independent of the pressure of the gas
C
the rate of dissociation of adsorbed molecules from the surface does not depend on the surface covered
D
the adsorption at a single site on the surface may involve multiple molecules at the same time
Answer :
the mass of gas striking a given area of surface is proportional to the pressure of the gas
According to Langmuir's Model of adsorption of a gas on a solid surface the mass of gas adsorbed $$(x)$$ per gram of the adsorbent $$(m)$$ is directly proportional to the pressure of the gas $$(p)$$ at constant temperature i.e.
$$\frac{{\text{x}}}{{\text{m}}} \propto {\text{p}}$$