Redox Reactions and Electrochemistry — CBSE Class 12 · 2009 · Delhi Board Question with Solution

a) Define molar conductivity of a substance and describe how, for weak and strong electrolytes, molar conductivity changes with the concentration of the solute. How is this change explained?
b) A voltaic cell is set up at 25°C with the following half-cells: Ag

^{+}

(0.001 M) | Ag and Cu

^{2 +}

(0.10 M) | Cu. What would be the voltage of this cell? (

E_{ce l l}^{\circ} = 0.46

Solution

(a) Molar conductivity is the conductance of the volume of solution containing one mole of electrolyte between electrodes of unit area a unit distance apart;

Λ_{m} = κ \times 1000/ C

.
Strong electrolytes:

Λ_{m}

decreases slowly and linearly with

c

; the ions are fully present, but interionic attractions retard them more at higher concentration (

Λ_{m} = Λ_{m}^{\circ} - A c

).
Weak electrolytes:

Λ_{m}

is low at moderate concentration and rises steeply on dilution, because the degree of dissociation — and hence the number of ions — increases sharply as

c \to 0

.
(b) Cu is the anode (Cu

^{2 +}

/Cu has the lower E°); cell reaction: Cu + 2Ag

^{+} \to

^{2 +}

+ 2Ag,

n = 2

E_{ce l l} = 0.46 - \frac{0.059}{2} lo g \frac{[ C u ^{2 +} ]}{[ A g ^{+} ] ^{2}} = 0.46 - 0.0295 lo g \frac{0.10}{( 1 0 ^{- 3} ) ^{2}}

= 0.46 - 0.0295 \times 5 = 0.46 - 0.1475

E_{ce l l} = 0.31 V

CBSE Class 12 Board · 2009 · Delhi · Subjective

CBSE Class 12 · 2009 · Delhi · Redox Reactions and ElectrochemistryLong Answer

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