Chapter 3 : Electrochemistry

Q. Depict the galvanic cell in which the reaction

Z n (s) + 2 A g^{+} (a q) \to Z n^{2 +} (a q) + 2 A g (s)

takes place. Further show:
(i) Which of the electrode is negatively charged?
(ii) The carriers of the current in the cell.
(iii) Individual reaction at each electrode.

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Q. Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.

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Q. Calculate the standard cell potentials of galvanic cell in which the following reactions take place:
(i)

2 C r (s) + 3 C d^{2 +} (a q) \to 2 C r^{3 +} (a q) + 3 C d

(ii)

F e^{2 +} (a q) + A g^{+} (a q) \to F e^{3 +} (a q) + A g (s)

Calculate the

Δ_{r} G^{⊖}

and equilibrium constant of the reactions

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Q. How much electricity in terms of Faraday is required to produce:

(i)

20 g

C a

from molten

C a C l_{2}

(ii)

40 g

A l

from molten

A l_{2} O_{3}

[Given : Molar mass of calcium & Aluminium are 40 g

m o l^{- 1}

& 27 g

m o l^{- 1}

respectively]

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Q. In the button cells widely used in watches and other devices the following reaction takes place:

Z n (s) + A g_{2} O (s) + H_{2} O (l) \to Z n^{2 +} (a q) + 2 A g (s) + 2 O H^{-} (a q)

Determine

Δ_{r} G^{θ}

and

E^{θ}

for the reaction.

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Q. Conductivity of

0.00241 M

acetic acid is

7.896 \times 10^{- 5} S c m^{- 1}

. Calculate its molar conductivity. If

\land_{m}^{0}

for acetic acid is

390.5 S c m^{2} m o l^{- 1}

, what is its dissociation constant?

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Q. Predict the products of electrolysis in each of the following:
(i) An aqueous solution of

A g N O_{3}

with silver electrodes.
(ii) An aqueous solution of

A g N O_{3}

with platinum electrodes.
(iii) A dilute solution of

H_{2} S O_{4}

with platinum electrodes.
(iv) An aqueous solution of

C u C l_{2}

with platinum electrodes

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Q. The conductivity of sodium chloride at

298 K

has been determined at different concentrations and the results are given below:

Concentration/M	$0.001$	$0.010$	$0.020$	$0.050$	$0.100$
$10^{2} k / S m^{- 1}$	$1.237$	$11.85$	$23.15$	$55.53$	$106.74$

Calculate

\land_{m}

for all concentrations and draw a plot between

\land_{m}

and

c^{1 / 2}

. Find the value of

\land_{m}^{0}

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Q. The conductivity of

0.20 M

solution of

K C l

298 K

0.0248 S c m^{- 1}

. Calculate its molar conductivity.

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Q. The resistance of a conductivity cell containing

0.001 M K C l

solution at

298 K

1500 Ω

. What is the cell constant if conductivity of

0.001 M K C l

solution at

298 K

0.146 \times 10^{- 3} S c m^{- 1}

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Q. Write the Nernst equation and emf of the following cells at

298 K

:
(i)

M g (s) | M g^{+ 2} (0.001 M) ∥ C u^{+ 2} (0.0001 M) | C u (s)

.
(ii)

F e (s) | F e^{+ 2} (0.001 M) ∥ H^{+} (1 M) | H_{2} (g) (1 b a r) | P t (s)

(iii)

S n (s) | S n^{2 +} (0.050 M) ∥ H^{+} (0.020 M) | H_{2} (g) (1 b a r) | P t (s)

(iv)

P t (s) | B r_{2} (l) | B r^{-} (0.010 M) ∥ H^{+} (0.030 M) | H_{2} (g) (1 b a r) | P t (s)

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Q. Using the standard electrode potentials given in Table

3.1

, predict if the reaction between the following is feasible:
(i)

F e^{3 +} (a q)

and

I^{-} (a q)

(ii)

A g^{+} (a q)

and

C u (s)

(iii)

F e^{3 +} (a q)

and

B r^{-} (a q)

(iv)

A g (s)

and

F e^{3 +} (a q)

(v)

B r_{2} (a q)

and

F e^{2 +} (a q)

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Q. Arrange the following metals in the order in which they displace each other from the solution of their salts.

A l, C u, F e, M g

and

Z n

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Q. How much charge is required for the following reductions?

(i)

1 m o l

A l^{3 +}

A l

(ii)

1 m o l

C u^{2 +}

C u

(iii)

1 m o l

{M n O_{4}}^{-}

M n^{2 +}

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Q. Three electrolytic cells

A, B, C

containing solutions of

Z n S O_{4}, A g N O_{3}

and

C u S O_{3}

, respectively are connected in series. A steady current of

1.5

amperes was passed through them until

1.45 g

of silver deposited at the cathode of cell

B

. How long did the current flow? What mass of copper and zinc were deposited?

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Q. How much electricity is required in coulomb for the oxidation of:
(i)

1 m o l

H_{2} O

O_{2}

?
(ii)

1 m o l

F e O

F e_{2} O_{3}

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Q. Given the standard electrode potentials,

K^{+} / K = - 2.93 V, A g^{+} / A g = 0.80 V,

H g^{2 +} / H g = 0.79 V, M g^{2 +} / M g = - 2.37 V, C r^{3 +} / C r = - 0.74 V

Arrange these metals in their increasing order of reducing power.

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