Electrochemistry Test

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Electrochemistry Test - 22

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Weekly Quiz Competition

Question 1
1 / -0

Maintenance-free batteries, now in use, in place of common batteries, have :

A
Electrodes made of lead-lead oxide

B
Electrodes made of calcium-containing lead alloy

C
Non-aqueous solvents as medium

D
Platinum electrodes

Solution

Calcium-tin-lead alloys are used for making grids for maintenance-free batteries. The calcium content in such alloys for positive grids has varied generally from about 0.06 to about 0.1% by weight of the alloy while the tin has generally ranged from about 0.1 up to 0.8% and even more. More typically, the calcium content in such alloys when used for making maintenance-free battery grids has been at least about 0.08% by weight or more.
B is correct
Question 2
1 / -0

Schematic diagram of an electrolytic-cell is:

A

B

C

D
none is correct presentation

Solution

In an electrolytic cell cations move towards cathode and anions move towards anode. In the external circuit, current flows from anode to cathode. Hence option B is correct.
Question 3
1 / -0

Which of the following oxide(s) of iron would be obtained on prolonged reaction of iron with steam?

A
$$FeO$$

B
$$Fe_2O_3$$

C
$$Fe_3O_4$$

D
$$Fe_2O_3$$ and $$Fe_3O_4$$

Solution

On prolonged heating with steam Fe produces $$Fe_3O_4$$ and release hydrogen gas. It is a mixed oxide of Fe.

$$3Fe+ 4H_2O \rightarrow Fe_3O_4(s) + 4H_2(g)$$
Question 4
1 / -0

The process of depositing a thin layer of desired metal over another metal by passing an electric current through some electrolyte is called as ?

A
electroplating

B
oxidation

C
electrotyping

D
electric shielding.

Solution

Electroplating is the process of coating a metal object with a thin layer of another metal by means of process which is known as Electrolysis. The electroplated coating is usually no more than .002 inch (.05 mm) thick.
Question 5
1 / -0

$$Al_2O_3$$ is reduced by electrolysis at low potentials and high currents. If $$4.0 \times 10^4$$ amperes of current is passed through molten $$Al_2O_3$$ for 6 hours, what mass of aluminium is produced? (Assume 100% current efficiency, at. mass of $$Al = 27 g \;mol^{-1})$$

A
$$1.3 \times 10^4\;g$$

B
$$9.0 \times 10^3\;g$$

C
$$8.1 \times 10^4\;g$$

D
$$2.4 \times 10^5\;g$$

Solution

$$W=z\times I\times t\\ z=\dfrac { molar\quad mass }{ nf\times 96500 } \\ z=\dfrac { 27 }{ 3\times 96500 } \\ W=\dfrac { 27 }{ 3\times 96500 } \times 4\times { 10 }^{ 4 }\times 6\times 60\times 60\\ \quad =8.1\times { 10 }^{ 4 }g$$
Question 6
1 / -0

$$E_{N{a^ + }/Na(s)}^0 = - 2.71V$$ , $$E_{M{g^{2 + }}/Mg(s)}^0 = - 2.37V$$, $$E_{F{e^{2 + }}/Fe(s)}^0 = - 0.44V$$ and $$E_{C{r^{3 + }}/Cr(s)}^0 = - 0.41V$$Based on this data, state which of the following is the weakest reducing agent.

A
$$Na^+$$

B
$$Na$$

C
$$Cr$$

D
$$Fe^{2+}$$

Solution

$$M+nX \rightarrow M^{n+}+nX^-$$
So higher the $$E^{\circ}_{M/M^{n-1}}$$ , stronger is that reducing agent.
$$E^{\circ}_{Na/Na^+}=2.71$$ is largest
$$\therefore $$ Na is strongest reducing agent
$$\therefore Na^+$$ is weakest reducing agent $$E^{\circ}_{Na^+/Na}$$ is least
Question 7
1 / -0

For the cell reaction : $$C{u^{2 + }}(aq)({C_1}) + Zn(s) \to Z{n^{2 + }}(aq)({C_2}) + Cu(s)$$ the change in free energy $$\Delta G$$ at a given temperature is a function of

A
$$ln C_1$$

B
$$ln (\dfrac{C_2}{C_1})$$

C
$$ln (C_2+ C_2)$$

D
$$ln (C_2)$$

Solution

We know $$ΔG = nFE $$
Again according to Nernst equation,
$$E=\dfrac{0.059}{n}log$$$$\dfrac{[Zn^{2+}]}{[Cu^{2+}]}$$ $$at$$ $$ 25^0C$$

So $$\Delta G$$ (free energy change) in an electrochemical cell at a given temperature is a function of
$$ln$$$$\dfrac{[Zn^{2+}]}{[Cu^{2+}]}=ln \dfrac {C_2}{C_1}$$
Question 8
1 / -0

Which is true according to the Faraday Law of electrolysis? Here $$m$$ is the mass deposited at an electrode, $$Q$$ is the charge at the electrode and $$I$$ is the current passed.

A
$$m\propto { I }^{ 2 }$$

B
$$m\propto Q$$

C
$$m\propto { Q }^{ 2 }$$

D
$$m$$ does not depend on $$Q$$

Solution

$$W=ZQ$$(according to Faradays law of electrolysis)
or $$m=ZQ$$
$$m=$$ mass deposited
$$m=Z\times I\times t$$
So $$m\propto Q$$
Question 9
1 / -0

Corrosion of iron pipes occurs in the presence of water. To prevent such corrosion, iron pipes are normally coated with an element like magnesium using electroplating.
Which of the following statements is correct?

A
During corrosion of an un-plated iron pipe, water is oxidized; during electroplating, iron acts as anode.

B
During corrosion of an un-plated iron pipe, oxygen is reduced; during electroplating, iron acts as cathode.

C
During corrosion of an un-plated iron pipe, iron is oxidised; during electroplating, magnesium is deposited on the anode.

D
During corrosion of an un-plated iron pipe, iron is reduced; during electroplating, magnesium is deposited on the cathode.
Question 10
1 / -0

According to Faraday's law of electrolysis, the amount of decomposition is proportional to:

A
1/time for which current passes

B
electrochemical equivalent of the substance

C
1/current

D
1/electrochemical equivalent

Solution

The amount of decomposition (i.e., mass of the substance liberated during electrolysis) is proportional to electro chemical equivalent of the substance.
Using the relation $$[m= Z*i*t]$$
where Z is its electrochemical equivalent , i is current , t is time and m is the mass deposited or liberated .
One can say that the amount of mass deposited will be proportional to the electrochemical equivalent of the substance.

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Electrochemistry Test - 22

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Electrochemistry Test - 22

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Question 1

Electrodes made of lead-lead oxide

Electrodes made of calcium-containing lead alloy

Non-aqueous solvents as medium

Platinum electrodes

Solution

Question 2

none is correct presentation

Solution

Question 3

$$FeO$$

$$Fe_2O_3$$

$$Fe_3O_4$$

$$Fe_2O_3$$ and $$Fe_3O_4$$

Solution

Question 4

electroplating

oxidation

electrotyping

electric shielding.

Solution

Question 5

$$1.3 \times 10^4\;g$$

$$9.0 \times 10^3\;g$$

$$8.1 \times 10^4\;g$$

$$2.4 \times 10^5\;g$$

Solution

Question 6

$$Na^+$$

$$Na$$

$$Cr$$

$$Fe^{2+}$$

Solution

Question 7

$$ln C_1$$

$$ln (\dfrac{C_2}{C_1})$$

$$ln (C_2+ C_2)$$

$$ln (C_2)$$

Solution

Question 8

$$m\propto { I }^{ 2 }$$

$$m\propto Q$$

$$m\propto { Q }^{ 2 }$$

$$m$$ does not depend on $$Q$$

Solution

Question 9

During corrosion of an un-plated iron pipe, water is oxidized; during electroplating, iron acts as anode.

During corrosion of an un-plated iron pipe, oxygen is reduced; during electroplating, iron acts as cathode.

During corrosion of an un-plated iron pipe, iron is oxidised; during electroplating, magnesium is deposited on the anode.

During corrosion of an un-plated iron pipe, iron is reduced; during electroplating, magnesium is deposited on the cathode.

Question 10

1/time for which current passes

electrochemical equivalent of the substance

1/current

1/electrochemical equivalent

Solution

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