Electrochemistry Test

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Electrochemistry Test - 27

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Weekly Quiz Competition

Question 1
1 / -0

A shiny brown-coloured element 'X' on heating in air becomes black in colour. Name the element 'X'?

A
Sodium

B
Calcium

C
Copper

D
Aluminium

Solution

'X' is copper (Cu) and the black-coloured compound formed is copper oxide(CuO). The equation of the reaction involved on heating copper is given below:

$$\underset{(Shiny\,brown\,in\,colour)}{2Cu} + O_2 \overset{Heat}{\rightarrow} \underset{(Black\,in\,colour)}{2CuO}$$
Question 2
1 / -0

Assertion: Rusting of Fe is quicker in saline water than in ordinary water.
Reason: Presence of $$Na^+$$ and $$Cl^-$$ ions increase the conductance of the saline water.

A
Both Assertion and Reason are true and Reason is the correct explanation of Assertion

B
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

C
Assertion is true but Reason is false

D
Assertion is false but Reason is true

E
Both Assertion and Reason are false

Solution

The $$Na^{\oplus}$$ and $$Cl^{\ominus}$$ present in saline water increase the conductance of the solution in contact with the metal surface. This accelerates the formation of $$Fe^{2+}$$ ions and hence that of rust, $$Fe_2O_3 \cdot xH_2O$$
Question 3
1 / -0

Assertion: The amount of charge carried by one mole electrons is the same as carried by one mole of $$K^{\oplus}$$ ions.
Reason: one mole electrons and one mole $$K^{\oplus}$$ ions carry one faraday charge each.

A
Both Assertion and Reason are true and Reason is the correct explanation of Assertion

B
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

C
Assertion is true but Reason is false

D
Assertion is false but Reason is true

E
Both Assertion and Reason are false

Solution

I F = 96500 C = Charge on 1 mole of $$e^{-}$$ = Charge on the $$l$$ Eq of anion.
Question 4
1 / -0

An electrochemical cell stops working after some time because:

A
electrode potential of both the electrodes becomes zero

B
electrode potential of both the electrodes become equal.

C
one of the electrode is eaten away.

D
the reaction starts proceeding in opposite direction

Solution

Correct option (B), the electrode potential of both the electrodes becomes equal.
Hint: An electrochemical cell converts chemical energy to electrical energy.

Explanation:

In an electrochemical cell, two electrodes are present in the solution of chemical species. One electrode is an anode that is negatively charged. Here the species release electrons and convert gets converted to cation. Another electrode is the cathode which is positively charged. Here the species accepts electrons and gets converted to an anion.

At equilibrium when the electrode potential of both the electrodes becomes equal then the cell stops working.

Final Answer: An electrochemical cell stops working after some time because the electrode potential of both electrodes becomes equal.
Question 5
1 / -0

calculate $$\Delta G_{f}^{\ominus}$$ of the reaction :
$$Ag^{\oplus}(aq)\, +\, Cl^{\ominus}(aq)\, \rightarrow\, AgCl(s)$$
Given : $$\Delta G^{\ominus_{AgCl}}\, =\, - 109\, kJ\, mol^{-1}$$
$$\Delta G^{\ominus}_{(Cl^{\ominus})}\, =\, -\, 129\, kJ\, mol^{-1}$$
$$\Delta G^{\ominus}_{(Ag^{\oplus)}}\, =\, -\, 77\, kJ\, mol^{-1}$$

A
$$-\, 97\, kJ\, mol^{-1}$$

B
$$-\, 57\, kJ\, mol^{-1}$$

C
$$57\, kJ\, mol^{-1}$$

D
$$97\, kJ\, mol^{-1}$$

Solution

$$Ag^{\oplus}(aq)\, +\, Cl^{\ominus}(aq)\, \rightarrow\, AgCl(s)$$
$$\Delta G_{f}^{\ominus}\, =\, \Delta G^{\ominus}_{AgCl)}\, -\,\Delta_{f} G^{\ominus}_{AgCl)}\, -\, \Delta _{f} G^{\ominus}_{(Ag^{\oplus})}\, -\, \Delta_ {f} G^{\ominus}_{(Cl^{\ominus})}$$
$$=\, -\, 109\, -\, 77\, -\, (-\, 129)\, =\, -\, 57\, kJ\, mol^{-1}$$
Question 6
1 / -0

The amount of charge carried by $$M^{3-}$$ ion is:

A
$$4.8 \times 10^{-19} C$$

B
$$7.4 \times 10^{-19} C$$

C
$$9.6 \times 10^{-19} C$$

D
none of the above

Solution

Charge of $$e^{-} = 1.60 \times 10^{-19} C$$

Charge on $$M^{3-} = 3 \times 1.6 \times 10^{-19} C = 4.8 \times 10^{-19} C$$

Option A is correct.
Question 7
1 / -0

The electric charge for electrode deposition of 1 g equivalent of a substance is:

A
1 ampere per second

B
96500 Coulombs per second

C
1 ampere for one hour

D
The charge on one mole of electrons

Solution

The quantity of electricity required to deposit or librate 1 g equivalent of any substance by the passage of electric current.
It is equal to the charge present on 1 mol of electrons. One faraday is equivalent to 96500 C.
Question 8
1 / -0

The charge carriers in metallic conductors and in electrolytes are respectively:

A
both ions

B
both electrons

C
electrons and ions

D
ions and electrons

Solution

Electrolysis is the passing of a direct electric current through an ionic substance that is either molten or dissolved in a suitable solvent, producing chemical reactions at the electrodes and separation of materials.

In metallic conductors, electrons carry the current and the material is unaffected by this flow for small currents.
Question 9
1 / -0

If $$E^{\ominus}_{Fe^{3+} | Fe}$$ and $$E^{\ominus}_{Fe^{2+} | Fe}$$ are $$-0.36 V$$ and $$-0.439 V$$, respectively, then the value of $$E^{\ominus}_{Fe^{3+} |
Fe^{2+}}$$ is:

A
$$(-36 0.439) V$$

B
$$[3(-0.36) + 2(-0.439)] V$$

C
$$(-0.36 0.0439) V$$

D
$$[3(-0.36) 2 (-0.439)] V$$

Solution

$$Fe^{3+}\, +\, 3e^-\, \rightarrow\, Fe:\, \Delta G_1\, =\, -3F\, E^{\ominus}_{Fe^{3+}\, +\, Fe}$$
$$Fe^{2+}\, +\, 2e^-\, \rightarrow\, Fe:\, \Delta G_2\, =\, -2F\, E^{\ominus}_{Fe^{2+}\,
|\, Fe}$$
$$Fe^{3+}\, e^-\, \rightarrow\, Fe^{2+}:\, \rightarrow\, \Delta G_3\, =\, -F\,
E^{\ominus}_{Fe^{2+}\, |\, Fe}$$
$$E^{\ominus}_{Fe^{3+}\, |\, Fe^{2+}}\, =\, 3E^{\ominus}_{Fe^{3+}\, |\, Fe}\, -\,
2E^{\ominus}_{Fe^{2+}\, |\, Fe}$$
$$[3(-0.36) + 2(-0.439)] V$$
Question 10
1 / -0

Total charge required to convert three moles of $$Mn_3O_4$$ to $$MnO_4^{-}$$ in alkaline medium will be:

A
$$10 F$$

B
$$20F$$

C
$$30 F$$

D
$$40 F$$

Solution

$$(Mn^{3/+8})_3\, \rightarrow\, 3Mn^{6+}\, +\, 10e^-$$
$$\therefore$$ 10 Faraday charge is required for conversion of 1 mol of $$Mn_3O_4\, to\, MnO_4^{2-}$$
so 30 faraday charge is required for 3 mole.

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Electrochemistry Test - 27

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Question 1

Sodium

Calcium

Copper

Aluminium

Solution

Question 2

Both Assertion and Reason are true and Reason is the correct explanation of Assertion

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

Assertion is true but Reason is false

Assertion is false but Reason is true

Both Assertion and Reason are false

Solution

Question 3

Both Assertion and Reason are true and Reason is the correct explanation of Assertion

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

Assertion is true but Reason is false

Assertion is false but Reason is true

Both Assertion and Reason are false

Solution

Question 4

electrode potential of both the electrodes becomes zero

electrode potential of both the electrodes become equal.

one of the electrode is eaten away.

the reaction starts proceeding in opposite direction

Solution

Question 5

$$-\, 97\, kJ\, mol^{-1}$$

$$-\, 57\, kJ\, mol^{-1}$$

$$57\, kJ\, mol^{-1}$$

$$97\, kJ\, mol^{-1}$$

Solution

Question 6

$$4.8 \times 10^{-19} C$$

$$7.4 \times 10^{-19} C$$

$$9.6 \times 10^{-19} C$$

none of the above

Solution

Question 7

1 ampere per second

96500 Coulombs per second

1 ampere for one hour

The charge on one mole of electrons

Solution

Question 8

both ions

both electrons

electrons and ions

ions and electrons

Solution

Question 9

$$(-36 0.439) V$$

$$[3(-0.36) + 2(-0.439)] V$$

$$(-0.36 0.0439) V$$

$$[3(-0.36) 2 (-0.439)] V$$

Solution

Question 10

$$10 F$$

$$20F$$

$$30 F$$

$$40 F$$

Solution

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