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Published on: 03/09/2019
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
Questions + Answers key
Take MCQ Chemistry Test
1.
How much amount of a substance is deposited by 1 coulomb ? What is it called ?
2.
Consult the table of standard electrode potentials and suggest three substances that can oxidize ferrous ions under suitable conditions.
3.
How will pH of brine (aq.NaCl solution) be affected when it is electrolysed?
4.
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: \({ E }_{ { Zn }^{ 2+ }/Zn }^{ o }=-0.76V;{ E }_{ { Cu }^{ 2+ }/Cu }^{ o }=+0.34V\)]
5.
When a certain electrolytic cell was filled with 0.1 M KCl, it has resistance of 85 ohms at 25 oC. When the same cell was filled with an aqueous solution of 0.052 M unknown electrolyte, the resistance was 96 ohms. Calculate the molar conductance of the electrolyte at this concentration. [Specific conductance of 0.1 M KCl = \(1.29\times { 10 }^{ -2 }{ ohm }^{ -1 }{ cm }^{ -1 }\)]
6.
If Zn2+ / Zn electrode is diluted 100 times, then the change in emf is
increase of 59 mV
decrease of 59 mV
increase of 29.5 mV
decrease of 29.5 mV
7.
A gas X at 1 atm is bubbled through a solution containing a mixture of 1M Y- and 1M Z- ions at 25°C . If the reduction potential of Z > Y > X, then
Y will oxidize X but not Z
Y will oxidize both X and Z
Y will oxidize Z but not X
Y will reduce both X and Z
8.
A hypothetical electrochemical cell is\(\overset { \circleddash }{ A } |{ A }^{ + }\left( xM \right) \parallel { { B }^{ + } }\left( yM \right) |\overset { \oplus }{ B } \) The emf measured is + 0.20 V. The cell reaction is
The cell reaction cannot be predicted
\(A+{ B }^{ + }\longrightarrow { A }^{ + }+B\)
\({ A }^{ + }+B\longrightarrow A+{ B }^{ + }\)
\({ A }^{ + }+{ e }^{ - }\longrightarrow A;{ B }^{ + }+{ e }^{ - }\longrightarrow B\)
9.
Which of the following solution has highest equivalent conductance ?
0.01 M KCl
0.05 M KCl
0.02 M KCl
0.005 M KCl
10.
A dilute aqueous solution of Na2 SO4 is electrolysed using platinum electrodes. The products at the anode and cathode are
O2 , H2
SO2 , Na
O2 , Na
S2 O82- , H2
1.
One coulomb deposits Eq.wt./96500 gram. It is called electrochemical equivalent of the substance.
2.
(i) \({ MnO }_{ 4 }^{ 1 }\) in acidic medium
(ii) \({ Cr }_{ 2 }{ O }_{ 7 }^{ 2- }\) in acidic medium
(iii) \({ H }_{ 2 }{ O }_{ 2 }\) in acidic medium
3.
It will increase due to formation of NaOH.
4.
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
5.
\(K=1.29\times { 10 }^{ -2 }{ ohm }^{ -1 }{ cm }^{ -1 }\)
\(K=\frac { 1 }{ R } \times \frac { 1 }{ a } \Rightarrow \frac { 1 }{ a } =K\times R=1.29\times { 10 }^{ -2 }\times 85=109.65\times { 10 }^{ -2 }=1.0965{ cm }^{ -1 }\)
\({ \wedge }_{ m }=\frac { 1000K }{ M } =\frac { 1000 }{ M } \times \frac { 1 }{ R } \times \frac { 1 }{ a } \)
\({ \wedge }_{ m }=\frac { 1000\times 1\times 1.0965 }{ 0.052\times 96 } =\frac { 1096.50 }{ 4.992 } =219.65 \ S \ { cm }^{ 2 }{ mol }^{ -1 }\)
6.
(b)
decrease of 59 mV
7.
Reduction potentials in the order Z > Y > X means that Z can be reduced most easily and X least easily, i.e., their oxidizing powers are : Z > Y > X.
Thus, Y will oxidize X but not Z.
8.
(b)
\(A+{ B }^{ + }\longrightarrow { A }^{ + }+B\)
9.
(d)
0.005 M KCl
10.
(a)
O2 , H2
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