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Published on: 20/09/2019
Electrochemistry
Download CBSE Class 12th Standard CBSE Chemistry question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Chemistry
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1.
Electrolysis of the solution of MnSO4 in aq sulphuric acid is a method for the preparation of MnO2 as per the chemical reaction
Mn2+ + 2H2O → MnO2 + 2H+ + H2
Passing a current of 27 A for 24 Hrs gives 1 kg of MnO2. What is the current efficiency ? What are the reactions occurring at anode and cathode?
2.
A 100W and 110 V incandescent lamp is connected in series with an electrolytic cell containing CdSO4 solution. What mass of cadmium will be deposited at the cathode after 4 hrs of electricity?
3.
Calculate the emf of the following cell at 25° C:
\(Fe|{ Fe }^{ 2+ }(0.01M)\parallel { H }^{ + }\left( 0.01M \right) { H }_{ 2 }(g)(1bar)|Pt(s)\)
\({ E }^{ ° }\left( { Fe }^{ 2+ }|Fe \right) =-0.44V{ E }^{ ° }\left( { H }^{ + }|{ H }_{ 2 } \right) =0.00V\)
4.
A solution of CuSO4 is electrolysed for 10 minutes with a current of 1-5 amperes. What is the mass of copper deposited at the cathode? (Molar mass of Cu = 63.5 g mol-1)
5.
The Eo values at 298 K corresponding to the following two reduction electrode processes are:
(i) Cu+/Cu = +0.52 V
(ii) Cu2+/Cu+ = +0.16 V
Formulate the galvanic cell for their combination. What will be the cell potential? Calculate the \({ \triangle }_{ r }{ G }^{ o }\) for the cell reaction.(1F = 96500 C mol-1).
6.
For the cell
\(Zn(s)\left| { Zn }^{ 2+ }(2M) \right| \left| { Cu }^{ 2+ }(0.5M) \right| Cu(s)\)
(a) Write equation for each half-reaction.
(b) Calculate the cell potential at 25 oC.
[Given: \({ E }_{ { Zn }^{ 2+ }/Zn }^{ o }=-0.76V;{ E }_{ { Cu }^{ 2+ }/Cu }^{ o }=+0.34V\)]
7.
An aqueous solution of copper sulphate, CuSO4 was electrolysed between platinum electrodes using a current of 0.1287 ampere for 50 minutes. (Atomic mass of Cu=63.5 g mol-1].
(a) Write the cathodic reaction.
(b) Calculate:
(i) Electric charge passed during electrolysis.
(ii) Mass of copper deposited at the cathode
[Given : 1F = 96,500 C mol-1]
8.
Calculate the standard cell potentials of galvanic cell in which the following reactions take place:
(i) \(2Cr(s)+{ 3Cd }^{ 2+ }(aq)\rightarrow { 2Cr }^{ 3+ }(aq)+3Cd(s)\)
(ii) \({ Fe }^{ 2+ }(aq)+{ Ag }^{ + }(aq)\rightarrow { Fe }^{ 3+ }(aq)+Ag(s)\)
Calculate the \({ \triangle }_{ r }{ G }^{ o }\) and equilibrium constant for the reactions.
9.
Which of the following has larger molar conductance:
a. 0.08 M soln. having conductivity equal to 2 × 10-2 ohm-1cm-1
b. 0.10 M soln. having resistivity equal to 5.8 ohm cm
1.
95 %
2.
Step I
Calculation of the quantity of charge passed:
We know that,
Watt = Ampere x Volt
Ampere =\(\frac { Watt }{ Volt } =\frac { 100 }{ 110 } \)
Now charge = Current x Time
=\(\left( \frac { 100 }{ 110 } amp \right) \times 4\times 60\times 60\)
= 13091 C
Step II
Calculation of mass of Cadmium deposited:
The cathodic reaction is
Cd2+(aq)+2e-\(\rightarrow\)Cd(s)
112.2g 2 x 96500C
2 x 96500 C of charge deposited Cd = 112.2 g
13091 C charge will deposite Cd
\(\frac { 112.2g }{ 2\times 96500C } \times 13091C\)
= 7.61g
3.
Cell reaction is
\({ Fe }_{ (s) }+{ 2{ H }^{ + } }_{ (aq) }\rightarrow { { Fe }^{ 2+ } }_{ (aq) }+{ H }_{ 2(g) }\)
\({ { E }^{ ° } }_{ cell }=0.00-(-0.44)=0.44V\)
\({ E }_{ cell }={ { E }^{ ° } }_{ cell }-\frac { 0.0591 }{ 2 } log\frac { \left[ { Fe }^{ 2+ } \right] }{ { \left[ { H }^{ + } \right] }^{ 2 } } \)
\(=0.44-\frac { 0.0591 }{ 2 } log\frac { 0.001 }{ { \left( 0.01 \right) }^{ 2 } } \)
=0.44 - 0.02955 = 0.41045 V
4.
0.296 g.
5.
For EMF to be +ve, oxidation should take place on electrode (ii), i.e., half-cell reactions will b
Cu++e- ⟶ Cu
Cu+ ⟶ Cu2++e-
Overall cell reaction: 2 Cu+ ⟶ Cu + Cu2+
Hence, the cell will be represented as : Cu+ I Cu2+ I I Cu+ I Cu
E0cell = E0Red(RHS) - E0Red(LHS) = 0.52-0.16 = 0.36
ΔrG0 = - n FEocell= - 1 x 96500 C mol-1 x 0·36 V = - 34740 CV mol-1 = - 34740 J mol-1
6.
Zn(s) ➝ Zn2+ (aq) + 2e-
Cu2+(aq) + 2e- ➝ Cu(s)
______________________________________
Zn(s) + Cu2+(aq) ➝ Zn2+(aq) + Cu(s)
______________________________________
\(E_{cell}=E^0_{cell}-{0.0591\over 2}log{[Zn^{2+}]\over [Cu^{2+}]}\)
\(=\left(E^0_{cu^{2+}/Cu}-E^0_{Zn^{2+}/Zn}\right)-{0.0591V\over 2}log{2\over 0.5}\)
\(=[+0.34V+0.76]-{0.0591V\over v2}log4\)
\(=+1.10V-{0 0591V\over 2}\times0.6021\)
= 1.10 V - 0.018 V = 1.082 V
7.
\(t=50\times 60=3000s\)
\(I=0.1287A\)
\((a) \ { Cu }^{ 2+ }+{ 2e }^{ - }\longrightarrow Cu(s) \ At \ cathode\)
\((b)(i) Q=I\times t=0.1287\times 3000=386.1C\)
\((ii) \ m=Z\times I\times t=\frac { 63.5 }{ 2\times 96500 } \times 386.1=0.127g\)
8.
(i) \(E^0_{cell}=E^0_{cathode}-E^0_{anode}= - 0·40 V - (- 0·74 V) = + 0·34 V\)
\(Δ_r G^0 - n FE^o_{cell}= - 6 mol \times 96500\ C\ mol.^{-1}\times 0·34 V\)
= -196860 CV mol-1 = -196860 J mol-1 = -196.86 k.J mol-1
- ΔrGo = 2.303 RT log K
196860 = 2.303 x 8.314 x 298 log K or log K = 34.5014
K = Antilog 34.5014 = 3.192 x 1034
(ii) E0cell = + 0.80 V - 0.77 V = + 0.03 V.
Δr G0 = - nF E0cell = - (1 mol) x (96500 C mol-1) x (0·03 V)
= - 2895 CV mol-1 = - 2895 J mol-1
= - 2.895 k.J mol-1
ΔrG0 = - 2.303 RT log K
- 2895 = - 2.303 x 8.314 x 298 x log K
or log K = 0.5074 or K = Antilog (0.5074) = 3.22.
9.
(a) \(\Lambda_{M}=\frac{1000 \times k}{M}=\frac{\left(1000 \mathrm{~cm}^{3}\right) \times\left(2.0 \times 10^{-2} \mathrm{ohm}^{-1} \mathrm{~cm}^{-1}\right)}{(0.08 \mathrm{~mol})}=250 \mathrm{\ ohm}^{-1} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\)
(b) \(\Lambda_{M}=\frac{1000 \times k}{M}=\frac{1000}{p \times M}=\frac{\left(1000 \mathrm{~cm}^{3}\right)}{(58 \operatorname{ohm} \mathrm{cm}) \times(0.1 \mathrm{~mol})}=172.41 \mathrm{\ ohm}^{-1} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}. \)
Solution (a) has larger molar conductance than solution (b).
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