UNIT 9: Electro Chemistry - Online Test
Charging : anode : PbSO4
(s)+ 2e− → Pb (s) +
SO4-2 (aq)
Cathode : PbSO4 (s)+
2H2 O (l) → PbO2 (s) + SO4-2
(aq)+2e−
Among the following cells
I) Leclanche cell
II) Nickel – Cadmium cell
III) Lead storage battery
IV) Mercury cell
EoZn2+|Zn = − 0.76V and EoFe2+|Fe = −0.44V
Zinc has higher negative electrode potential than iron, iron cannot be coated
on zinc.
Assertion : pure iron when heated in dry air is
converted with a layer of rust.
Both are
false
i) Dry
air has no reaction with iron
ii) Rust
has the composition Fe2 O3 . x H2O
17. The equivalent conductance of M/36 solution of a weak monobasic acid
is 6 mho cm2 equivalent –1 and at infinite dilution is
400 mho cm2 equivalent –1. The dissociation constant of
this acid is
α = Λ / Λo = 6/400
Ka =α2C
= 6/400 × 6/400 × 1/36
= 6.25 ×10−6
R = ρ. l/A
cell constant = R/ρ
= κ.R (1/ ρ =κ )
= 1.25 × 10−3 Ω−1cm−1
× 800 Ω
= 1 cm−1
Zn(s) → Zn2+ (aq) + 2e-
Cu2+ (aq)+2e-
→ Cu(s)
Zn(s) +Cu2+ (aq) → Zn2+
(aq) + Cu(s)
Ecell =Eºcell – (0.0591/2) log ( [zn2+]/
[Cu2+] )
E1 =Eºcell - 0.0591/2 log (10-2/1)
E1 =Eocell
+ 0.0591 ........(1)
E2 =Eºcell - 0.0591/2 log (1/10-2)
E2 =Eocell
- 0.0591 .........(2)
E1>E2
