141.
The number of electrons delivered at the cathode during electrolysis by a current of $${\text{1 ampere}}$$ in 60 seconds is ( charge on electron $${\text{ = 1}}{\text{.60}} \times {\text{1}}{{\text{0}}^{ - 19}}C$$ )
$$\eqalign{
& {\text{From Faraday's}}\,{\text{first law of electrolysis,}} \cr
& \frac{w}{E} = \frac{{it}}{{96500}}\,\,\,...{\text{(i)}} \cr
& {\text{Given,}}\,i = 1\,A;\,t = 60\,s \cr
& {\text{Putting these values in Eq}}.{\text{(i), we get}} \cr
& \frac{w}{E} = \frac{{1 \times 60}}{{96500}}\,\,{\text{or}}\,\,\frac{w}{E} = \frac{6}{{9650}} \cr
& = {\text{Number of mole of electrons}} \cr
& \therefore \,\,{\text{Number of electrons}} \cr
& = \frac{6}{{9650}} \times 6.022 \times {10^{23}} \cr
& = 3.75 \times {10^{20}} \cr} $$
142.
A graph was plotted between molar conductivity of various electrolytes $$\left( {NaCl,HCl\,{\text{and}}\,{\text{N}}{{\text{H}}_4}OH} \right)$$ and $$\sqrt c \left( {{\text{in}}\,mol\,{L^{ - 1}}} \right).$$ Correct set is :
A
$$I\left( {NaCl} \right),II\left( {HCl} \right),III\left( {N{H_4}OH} \right)$$
B
$$I\left( {HCl} \right),II\left( {NaCl} \right),III\left( {N{H_4}OH} \right)$$
C
$$I\left( {N{H_4}OH} \right),II\left( {NaCl} \right),III\left( {HCl} \right)$$
D
$$I\left( {N{H_4}OH} \right),II\left( {HCl} \right),III\left( {NaCl} \right)$$
Ionic molar conductivity of $${H^ + }$$ is very high and $$N{H_4}OH$$ is a weak electrolyte.
143.
The standard reduction potentials at $${25^ \circ }C$$ of $$\frac{{L{i^ + }}}{{Li}},\frac{{B{a^{2 + }}}}{{Ba}},\frac{{N{a^ + }}}{{Na}}$$ and $$\frac{{M{g^{2 + }}}}{{Mg}}$$ are – 3.03, – 2.73, – 2.71 and – 2.37 $$volt$$ respectively. Which one of the following is the strongest oxidising agent?
Higher the reduction potential, stronger is the oxidising agent.
144.
Electrolysis of dilute aqueous $$NaCl$$ solution was carried out by passing 10 milli ampere current. The time required to liberate 0.01 mol of $${H_2}$$ gas at the cathode is $$\left( {1\,{\text{Faraday}} = 96500\,C\,mo{l^{ - 1}}} \right)$$
$${\text{Give}}:\,I = 10\,{\text{milliamperes ;}}$$ $$IF = 96500{\text{ }}C{\text{ }}mo{l^{ - 1}}$$
$$\eqalign{
& t = ?\,;\,{\text{Moles of}}\,{H_2}{\text{produces = 0}}{\text{.01 }}mol \cr
& {\text{From the law of electrolysis, we have }} \cr
& {\text{Equivalents of}}\,{H_2}\,{\text{produces}} = \frac{{I \times t\left( {\sec } \right)}}{{96500}} \cr
& {\text{Substituting given values, we get}} \cr
& 0.01 \times 2 = \frac{{10 \times {{10}^{ - 3}}\left( {{\text{amperes}}} \right) \times t\left( {\sec } \right)}}{{96500}} \cr
& {\text{or}}\,\,t = \frac{{0.01 \times 2 \times 96500}}{{10 \times {{10}^{ - 3}}}}\sec \cr
& \,\,\,\,\,\,\,\,\,\,\, = 19.3 \times {10^4}\sec . \cr
& {\text{i}}{\text{.e}}{\text{. (B) is the correct answer}}{\text{. }} \cr} $$
145.
Given : $${E^o}_{\frac{{F{e^{3 + }}}}{{Fe}}} = - 0.036V,$$ $${E^o}_{\frac{{F{e^{2 + }}}}{{Fe}}} = - 0.439\,V.$$ The value of standard electrode potential for the change, $$F{e^{3 + }}\left( {aq} \right) + {e^ - } \to F{e^{2 + }}\left( {aq} \right)$$ will be :