Question

447 Calculate EMF of the cell
A | A+ (0.1m) || B+2 (0.01m) B
Given E° A | A+3 = 0.75 V
EºB | B+2 = 0.45 V
(1) 0.30 V
(2) 1.21 v
(3) 0.26 V
(4) 0.80 V


ans. is 3 but how​

Answer 1

Answer:

Fe

2+

+2e

−

→Fe E

o

=−0.440 V....(i)

Fe

3+

+3e

−

→Fe E

o

=−0.036 V....(ii)

To calculate, Fe

3+

+e

−

→Fe

2+

E

o

=?

Reversing equation (i)

Fe→Fe

2+

+2e

−

....(iii) E

o

=0.440 V

Adding equation (iii) and (ii)

Fe→Fe

2+

+2e

−

E

o

=0.440 V

Fe

3+

+3e

−

→Fe E

o

=−0.036 V

__________________________

Fe

3+

+e

−

→Fe

2+

__________________________

E

o

=0.440−0.036=

Answer 2

$\frac{A}{A^{3+} } (0.1m) // \frac{B^{2+} }{B} 0.01m) \\ \\\frac{A}{A^{3+} } = 0.75v \\ \\ \frac{B}{B^{2}+} = 0.45v$