291.
A current of $$2.0\,A$$ passed for 5 hours through a molten metal salt deposits $$22.2\,g$$ of metal $$\left( {At\,wt. = 177} \right).$$ The oxidation state of the metal in the metal salt is
A
+1
B
+2
C
+3
D
+4
Answer :
+3
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$$\eqalign{
& m = \frac{{E.wt \times Q}}{{96500}}; \cr
& \therefore \,\,E.wt = \frac{{w \times 96500}}{Q} \cr
& = \frac{{22.2 \times 96500}}{{2 \times 5 \times 60 \times 60}} \cr
& = 60.3 \cr
& {\text{Oxidation state}} = \frac{{At\,wt.}}{{Eq.\,wt.}} \cr
& = \frac{{177}}{{60.3}} \cr
& = 3 \cr} $$
292.
The reduction potential of hydrogen half-cell will be negative if :
A
$$p\left( {{H_2}} \right) = 1\,{\text{atm}}\,{\text{and}}\left[ {{H^ + }} \right] = 2.0\,M$$
B
$$p\left( {{H_2}} \right) = 1\,{\text{atm}}\,{\text{and}}\left[ {{H^ + }} \right] = 1.0\,M$$
C
$$p\left( {{H_2}} \right) = 2\,{\text{atm}}\,{\text{and}}\left[ {{H^ + }} \right] = 1.0\,M$$
D
$$p\left( {{H_2}} \right) = 2\,{\text{atm}}\,{\text{and}}\left[ {{H^ + }} \right] = 2.0\,M$$
Answer :
$$p\left( {{H_2}} \right) = 2\,{\text{atm}}\,{\text{and}}\left[ {{H^ + }} \right] = 1.0\,M$$
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$$\eqalign{
& {H^ + } + {e^ - } \to \frac{1}{2}{H_2};E = {E^o} - \frac{{0.059}}{1}\log \frac{{P_{{H_2}}^{\frac{1}{2}}}}{{\left[ {{H^ + }} \right]}} \cr
& {\text{Now}}\,{\text{if}}\,{P_{{H_2}}} = 2\,{\text{atm}}\,{\text{and}}\,\left[ {{H^ + }} \right] = 1M \cr
& {\text{then}}\,E = 0 - \frac{{0.059}}{1}\log \frac{{{2^{\frac{1}{2}}}}}{1} = - 2 \cr} $$
293.
A dilute aqueous solution of $$N{a_2}S{O_4}$$ is electrolyzed using
platinum electrodes. The products at the anode and cathode are :
A
$${O_2},{H_2}$$
B
$${S_2}O_8^{2 - },Na$$
C
$${O_2},Na$$
D
$${S_2}O_8^{2 - },{H_2}$$
Answer :
$${O_2},{H_2}$$
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$${H_2}O$$ is more readily reduced at cathode than $$N{a^ + }.$$ It is also more readily oxidized at anode than $$SO_4^{2 - }.$$ Hence, the electrode reactions are
$$\eqalign{
& 2{H_2}O + 2{e^ - } \to {H_2} \uparrow + 2O{H^ - }\left[ {{\text{at cathode}}} \right] \cr
& {H_2}O \to \frac{1}{2}{O_2} \uparrow + 2{H^ + } + 2{e^ - }\left[ {{\text{at anode}}} \right] \cr} $$
294.
Mark the correct relationship from the following :
A
Equilibrium constant is related to $$emf$$ as $$\log \,K = \frac{{nFE}}{{2.303\,RT}}$$
B
$$EMF$$ of a cell $$Zn\left| {Zn_{\left( {{a_1}} \right)}^{2 + }} \right|\left| {Cu_{\left( {{a_2}} \right)}^{2 + }} \right|Cu$$ is $$E = {E^ \circ } - \frac{{0.591}}{n}\log \frac{{\left[ {{a_2}} \right]}}{{\left[ {{a_1}} \right]}}$$
C
Nernst equation is $${E_{{\text{cell}}}} = $$ $$E_{{\text{cell}}}^ \circ - \frac{{0.0591}}{n}\log \frac{{\left[ {{\text{Products}}} \right]}}{{\left[ {{\text{Reactants}}} \right]}}$$
D
For the electrode $$\frac{{{M^{n + }}}}{M}$$ at $$298\,K;$$ $$E = {E^ \circ } + \frac{{0.591}}{n}\log \left[ {{M^{n + }}} \right]$$
Answer :
Nernst equation is $${E_{{\text{cell}}}} = $$ $$E_{{\text{cell}}}^ \circ - \frac{{0.0591}}{n}\log \frac{{\left[ {{\text{Products}}} \right]}}{{\left[ {{\text{Reactants}}} \right]}}$$
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$$\left( {\text{A}} \right)\log \,K = \frac{{nFE_{{\text{cell}}}^ \circ }}{{2.303\,RT}}$$
$$\left( {\text{B}} \right){E_{{\text{cell}}}} = E_{{\text{cell}}}^ \circ - \frac{{0.0591}}{2}\log \frac{{\left[ {{a_1}} \right]}}{{\left[ {{a_2}} \right]}}$$
$$\left( {\text{D}} \right)$$ Expression at $$298\,K,$$ is $$E = {E^ \circ } + \frac{{0.0591}}{n}\log \left[ {{M^{n + }}} \right]$$
295.
$$AgN{O_3}\left( {aq.} \right)$$ was added to an aqueous $$KCl$$ solution gradually and the conductivity of the solution was measured. The plot of conductance $$\left( \Lambda \right)$$ versus the volume of $$AgN{O_3}\left( {aq.} \right)$$
A
$$(P)$$
B
$$(Q)$$
C
$$(R)$$
D
$$(S)$$
Answer :
$$(S)$$
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$$AgN{O_3}\left( {aq} \right) + KCl\left( {aq} \right) \to AgCl\left( s \right) + KN{O_3}\left( {aq} \right)$$
Conductivity of the solution is almost compensated due to formation of $$KN{O_3}\left( {aq} \right).$$ However, after at end point, conductivity increases more rapidly due to audition of excess $$AgN{O_3}$$ solution.
296.
The electrode potential $${E_{\left( {\frac{{Z{n^{2 + }}}}{{Zn}}} \right)}}$$ of a zinc electrode at $${25^ \circ }C$$ with an aqueous solution of $$0.1\,M\,ZnS{O_4}$$ is $$\left[ {E_{\left( {{{Z{n^{2 + }}} \over {Zn}}} \right)}^ \circ = - 0.76\,V.{\rm{Assume}}\,{{2.303RT} \over F} = 0.06\,{\rm{at}}\,298\,K} \right].$$
A
$$+0.73$$
B
$$-0.79$$
C
$$-0.82$$
D
$$-0.70$$
Answer :
$$-0.79$$
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$$\eqalign{
& {\text{For}}\,\,Z{n^{2 + }} \to Zn \cr
& {E_{\frac{{Z{n^{2 + }}}}{{Zn}}}} = E_{\frac{{Z{n^{2 + }}}}{{Zn}}}^ \circ - \frac{{2.303RT}}{{nF}}\log \frac{{\left[ {Zn} \right]}}{{\left[ {Z{n^{2 + }}} \right]}} \cr
& = - 0.76 - \frac{{0.06}}{2}\log \frac{1}{{\left[ {0.1} \right]}} \cr
& = - 0.76 - 0.03 \cr
& {E_{\frac{{Z{n^{2 + }}}}{{Zn}}}} = - 0.79\,V \cr} $$
297.
$$4.5$$ $$g$$ of aluminium ( atomic mass $$27u$$ ) is deposited at cathode from $$A{l^{3 + }}$$ solution by a certain quantity of electric charge. The volume of hydrogen produced at $$STP$$ from $${H^ + }\,ions$$ in solution by the same quantity of electric charge will be
A
44.8$$\,L$$
B
22.4$$\,L$$
C
11.2$$\,L$$
D
5.6$$\,L$$
Answer :
5.6$$\,L$$
View Solution
Discuss Question
$$\eqalign{
& {\text{From second law of Faraday}} \cr
& \,\,\,\,\,\,\frac{{{m_{Al}}}}{{{m_H}}} = \frac{{{E_{Al}}}}{{{E_H}}} \cr
& \,\,\,\,\,\,\frac{{4.5}}{{{m_H}}} = \frac{{\frac{{27}}{3}}}{1} \cr
& {\text{or}}\,\,\,{m_H} = 0.5\,g \cr
& \because \,\,{\text{Volume of}}\,\,2\,g\,{H_2}\,{\text{at}}\,STP = 22.4\,L \cr
& \therefore \,\,{\text{Volume of}}\,\,0.5\,g\,{H_2}\,{\text{at}}\,STP \cr
& \,\,\,\,\,\, = \frac{{22.4 \times 0.5}}{2}L \cr
& \,\,\,\,\,\, = 5.6\,L \cr} $$
298.
Which of the following is not an application of electrochemical series?
A
To compare the relative oxidising and reducing power of substances.
B
To predict evolution of hydrogen gas on reaction of metal with acid.
C
To predict spontaneity of a redox reaction.
D
To calculate the amount of metal deposited on cathode.
Answer :
To calculate the amount of metal deposited on cathode.
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Faraday's law is used in calculating the amount of metal deposited on cathode.
299.
On the basis of the following $${E^ \circ }$$ values, the strongest oxidising agent is
$${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }} \to {\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }} + {e^ - };$$ $${E^ \circ } = - 0.35\,V$$
$$F{e^{2 + }} \to F{e^{3 + }} + {e^ - };$$ $${E^ \circ } = - 0.77\,V$$
A
$${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }}$$
B
$$F{e^{2 + }}$$
C
$$F{e^{3 + }}$$
D
$${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }}$$
Answer :
$$F{e^{3 + }}$$
View Solution
Discuss Question
Substance which have higher reduction potential are stronger oxidising agent.
$${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }} \to {\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }} + {e^ - },$$ $${E^ \circ } = - 0.35\,V$$
$$\eqalign{
& F{e^{2 + }} \to F{e^{3 + }} + {e^ - },\,{E^ \circ } = - 0.77\,V \cr
& \because \,\,E_{oxi}^ \circ = - E_{red}^ \circ \cr} $$
$$\therefore \,{\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{3 - }} + {e^ - } \to {\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }},$$ $${E^ \circ } = 0.35\,V$$
$$F{e^{3 + }} + {e^ - } \to F{e^{2 + }},\,\,{E^ \circ } = 0.77\,V$$
Hence, $$F{e^{3 + }}$$ has maximum tendency to reduced, so it is the strongest oxidising agent.
300.
On passing current through two cells, connected in series containing solution of $$AgN{O_3}$$ and $$CuS{O_4},0.18\,g$$ of $$Ag$$ is deposited. The amount of the $$Cu$$ deposited is :
A
0.529$$\,g$$
B
10.623$$\,g$$
C
0.0529$$\,g$$
D
1.2708$$\,g$$
Answer :
0.0529$$\,g$$
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Discuss Question
$$\eqalign{
& {\text{Using Faraday's second law of electrolysis,}} \cr
& \frac{{{\text{Weight of }}Cu{\text{ deposited}}}}{{{\text{Weight of }}Ag{\text{ deposited}}}} = \frac{{Equ.\,wt.\,{\text{of}}\,Cu}}{{Equ.\,wt.\,{\text{of}}\,Ag}} \cr
& \Rightarrow \frac{{{w_{Cu}}}}{{0.18}} = \frac{{63.5}}{2} \times \frac{1}{{108}} \cr
& \Rightarrow {w_{Cu}} = \frac{{63.5 \times 18}}{{2 \times 108 \times 100}} \cr
& = 0.0529\,g. \cr} $$