Electrochemistry Test

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Electrochemistry Test - 42

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Weekly Quiz Competition

Question 1
1 / -0

The standard reduction potential for $$Zn^{2+}/ Zn, Ni^{2+}/ Ni$$ and $$Fe^{2+}/ Fe$$ are $$-0.76, 0.23$$ and $$-0.44\ V$$, respectively.

The reaction, $$X + Y^{2+} \rightarrow X^{2+} + Y$$ will be spontaneous when

A
$$X = Ni, Y = Fe$$

B
$$X = Ni, Y = Zn$$

C
$$X = Fe, Y = Zn$$

D
$$X = Zn, Y = Ni$$

Solution

The reaction is spontaneous when $$\triangle G < 0$$ and $$E_{cell}^{\circ} > 0$$.

$$\because \triangle G = -nFE^{\circ}$$ and $$E^{\circ} > 0$$

Also, $$E^{\circ}_{cell} = E^{\circ}_{oxi} + E^{\circ}_{red}$$ (or) $$E^{\circ}_{cathode} - E^{\circ}_{anode}$$

Here, $$E^{\circ}_{cell}$$ for

(a) $$-0.67\ V$$, i.e. $$E^{\circ}_{cell} < 0$$ (b) $$-0.99\ V$$, i.e. $$E^{\circ}_{cell} < 0$$

(c) $$-0.32\ V$$, i.e. $$E^{\circ}_{cell} < 0$$ (d) $$0.99\ V$$, i.e. $$E^{\circ} > 0$$.
Question 2
1 / -0

Which one is/ are correct among the following?
Given, the half cell emf's $$E^{0}_{Cu^{+2}/ Cu} = 0.337, E^{0}_{Cu^{+1}/ Cu} = 0.521$$.

A
$$Cu^{+1}$$ disproporationates

B
$$Cu$$ and $$Cu^{2+}$$ comproportionates (reverse of disproportionation into $$Cu^{+}$$).

C
$$E^{0}_{Cu/ Cu^{+2}} + E^{0}_{Cu^{+2}/ Cu}$$ is positive

D
All of these

Solution

$$\begin{array}{l} Cu\left| { C{ U^{ 2+ } } } \right. \parallel C{ u^{ + } }\left| { { C_{ 4 } } } \right. \\ E_{ cell }^{ ^{ \circ } }=E_{ Cathode }^{ ^{ \circ } }-E_{ anode }^{ ^{ \circ } } \\ \Rightarrow 0.521-0.337\Rightarrow +ve\, \, value. \end{array}$$
So, Reaction is
$$\begin{array}{l} Cu\to C{ u^{ 2+ } }+2{ e^{ - } }\to \left( i \right) & \\ 2C{ u^{ + } }\to 2{ e^{ - } }\to 2Cu\to \left( { ii } \right) & \\ 2C{ u^{ + } }\to C{ u^{ 2+ } }+Cu & C{ u^{ + } }\, \, is\, \, disproportinates. \\ Cu+C{ u^{ 2+ } }\, \, comproportionates & \end{array}$$
Option D is correct. All of these.
Question 3
1 / -0

$$1000\ mL\ of\ 1\ M\ CuSO_{4}(aq)$$ is electrolysed by $$9.65$$ ampere current for $$100$$ sec using $$Pt-electrode$$. Which of the following is incorrect statement?

A
Blue colour intensity decreases during electrolysis

B
Blue colour intensity remains constant if $$Cu-electrode$$ used

C
$$pH$$ of solution is $$8$$ after electrolysis

D
$$28\ mL$$ of $$CH_{4}$$ (at $$1\ atm$$ and $$273\ K)$$ undergoes combustion by $$O_{2}$$, liberated during electrolysis

Solution
Question 4
1 / -0

In hydrogen-oxygen fuel cell the carbon rods are immersed in hot aqueous solution of.

A
$$KCl$$

B
$$KOH$$

C
$$H_2SO_4$$

D
$$NH_4Cl$$

Solution

In the hydrogen-oxygen fuel cell, the carbon rods are immersed in hot aqueous solution of KOH (potassium hydroxide). KOH dissociates to provide hydroxide ions. Both anodic half reaction and cathodic half reaction involve hydroxide ions.

$$\displaystyle 2H_2+4OH^- \rightarrow 4H_2O+4e^-$$

$$\displaystyle O_2+2H_2O +4e^- \rightarrow 4OH^-$$
Question 5
1 / -0

Consider the following equations for a cell reaction
$$A + B \rightleftharpoons C+D$$ $$ E^0=x\,volt,k_{eq}=k_1$$
$$2A+2B \rightleftharpoons 2C+2D $$ $$E^0=y\, volt,k_{eq}=K_2$$ then:

A
$$x=y,K_1=k_2$$

B
$$x=2y,K_1=2k_2$$

C
$$x=y,K^2_1=k_2$$

D
$$x^2=y,K^2_1=k_2$$

Solution
Question 6
1 / -0

Among the following cells, which of the following are primary cells?

(I) Leclanche cell
(II) Nickle-Cadmium cell
(III) Lead Storage battery
(IV) Mercury cell

A
I and II

B
I and III

C
I and IV

D
III and IV

Solution

A primary cell is a battery that is designed to be used once and discarded, and not recharged with electricity and reused.

Leclanche cell and Mercury cell are primary cells whereas Nickle-Cadmium cell and Lead Storage battery are secondary cells.

Hence, option C is correct.
Question 7
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$$H_{2}(g)$$ and $$O_{2}(g)$$, can be produced by the electrolysis of water. What total volume (in $$L$$) of $$O$$ and $$H_{2}$$ are produced at $$STP$$ when a current of $$30\ A$$ is passed through a $$K_{2}SO_{4}(aq)$$ solution for $$193\ min.$$?

A
20.16

B
40.32

C
60.48

D
80.64

Solution

SOLUTION:
When 30 amperes is passed for 193 minutes, the quantity of current passed =193×60×30=347400 coulombs.
convering into faraday we get
$$\rightarrow \dfrac{347400}{96500}=3.6 Faraday.$$
$$H_2O\xrightarrow[k_2so_4 (aq.)]{electrolysis} \dfrac{1}{2}O_2+H_2$$
On passing 3.6 Faradays of electricity 3.6 moles of Hydrogen and (3.6×0.5)=1.8 moles of Oxygen will be formed.
Volume of oxygen produced at STP =1.8×22.4=40.32 liters.
hence the correct opt: B
Question 8
1 / -0

6.5 g $$Mg$$ deposits on electrolysis of $$MgCl_2$$ (fused) then what will be the volume of chlorine gas at STP discharged at electrode?

A
6.067 L

B
3.033 L

C
9.1 L

D
12.133 L

Solution

$$1$$ mole of $$MgCl_2$$ gives $$1mol$$ of $$Mg(24g)$$ & one mole of $$Cl_2$$
$$24g$$ of $$Mg=22.4dm^3$$ of $$Cl_2$$ gas at STP
$$\therefore 6.5g$$ of $$Mg=\cfrac {22.4\times 6.5}{24}$$
$$=6.067L$$ of $$Cl_2$$ gas
Question 9
1 / -0

An electrolytic cell is composed of $$Cu$$ and $$Zn$$. A current of $$9.65\ A$$ is drawn from a cell for $$1$$ hour. Then the loss in mass at anode and gain in mass at cathode, respectively could be:

A
$$11.77\ g, 11.43\ g$$

B
$$11.77\ g, 10\ g$$

C
$$22.86\ g, 23.54\ g$$

D
$$23.54\ g, 22.86\ g$$

Solution

$$W=\cfrac { I\times t\times M }{ nF } $$
$$I \rightarrow$$ current
$$t \rightarrow$$ time
$$W \rightarrow$$ weight deposited
$$M \rightarrow$$ Molar mass
$$n \rightarrow$$ No. of electrons involved
$$F \rightarrow$$ faraday's constant$$=96500$$
For Copper $$(Cu)$$
$$M=63.5$$g/mol
$$n=2$$
$$I=9.65$$A
$$t=1$$hr $$=3600$$sec
$$W=\cfrac { 9.65\times 3600\times 63.5 }{ 2\times 96500 } \\ W=11.43g$$
For Zinc $$(Zn)$$
$$M=65.38$$g/mol
$$n=2$$
$$W=\cfrac { 9.65\times 3600\times 65.38 }{ 2\times 96500 } =11.77g$$
Question 10
1 / -0

For the cell prepared from electrode $$A$$ and $$B$$, electrode $$A:$$ $$\displaystyle\frac{Cr_2O^{2-}_7}{Cr^{3+}}$$, $$E^0_{red}=+1.33$$V and electrode $$B:$$ $$\displaystyle\frac{Fe^{3+}}{Fe^{2+}}$$, $$E^0_{red}=0.77$$V, which of the following statement is not correct?

A
The electrons will flow from $$B$$ to $$A$$ (in the outer circuit) when connections are made.

B
The standard e.m.f. of the cell will be $$0.56$$V

C
$$A$$ will be positive electrode

D
Current flows from B to A in external circuit.

Solution

(A) The electrons will flow from B to A when
connection are made.
This statement is wrong because electrons will move
from A to B as electrons move from higher potential
$$ +1.33V $$ to the lower potential $$0.77V.$$

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Electrochemistry Test - 42

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Electrochemistry Test - 42

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Question 1

$$X = Ni, Y = Fe$$

$$X = Ni, Y = Zn$$

$$X = Fe, Y = Zn$$

$$X = Zn, Y = Ni$$

Solution

Question 2

$$Cu^{+1}$$ disproporationates

$$Cu$$ and $$Cu^{2+}$$ comproportionates (reverse of disproportionation into $$Cu^{+}$$).

$$E^{0}_{Cu/ Cu^{+2}} + E^{0}_{Cu^{+2}/ Cu}$$ is positive

All of these

Solution

Question 3

Blue colour intensity decreases during electrolysis

Blue colour intensity remains constant if $$Cu-electrode$$ used

$$pH$$ of solution is $$8$$ after electrolysis

$$28\ mL$$ of $$CH_{4}$$ (at $$1\ atm$$ and $$273\ K)$$ undergoes combustion by $$O_{2}$$, liberated during electrolysis

Solution

Question 4

$$KCl$$

$$KOH$$

$$H_2SO_4$$

$$NH_4Cl$$

Solution

Question 5

$$x=y,K_1=k_2$$

$$x=2y,K_1=2k_2$$

$$x=y,K^2_1=k_2$$

$$x^2=y,K^2_1=k_2$$

Solution

Question 6

I and II

I and III

I and IV

III and IV

Solution

Question 7

20.16

40.32

60.48

80.64

Solution

Question 8

6.067 L

3.033 L

9.1 L

12.133 L

Solution

Question 9

$$11.77\ g, 11.43\ g$$

$$11.77\ g, 10\ g$$

$$22.86\ g, 23.54\ g$$

$$23.54\ g, 22.86\ g$$

Solution

Question 10

The electrons will flow from $$B$$ to $$A$$ (in the outer circuit) when connections are made.

The standard e.m.f. of the cell will be $$0.56$$V

$$A$$ will be positive electrode

Current flows from B to A in external circuit.

Solution

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