Question

An aqueous Snl, solution is electrolyzed under 1 bar pressure using platinum electrodes. (a) Write the half-reactions predicted to occur at the anode and cathode, based on the standard cell potentials given below. Standard Reduction Potentials (Volts) at 25°C 12(s) +2 — 21'(aq) 0.535 O2(g) + 4 H30* (aq) + 4 —6H20(1) 1.229 2 H20(1) + 2 € H2(g) + 2 OH'(aq) -0.828 Sn²+(aq) +2 € + Sn(s) -0.140 Half-reaction at anode: Half-reaction at cathode: (b) What is the expected decomposition potential? the expected decomposition potential? V

Answer 1

According to Faraday's First law of electrolysis

a)

Mass of substance deposited in grams = (Atomic mass / valency) X (current in amperes X time in seconds)/96500 coulombs

Therefore,

Mass in g = (24 g.mol^-1 /2) X (5.13 X 10⁴ A X 11.9 days X 24 hours X 60 minutes X 60 seconds)/96500 C

Mass = 655.89 g.

(Note : 1 day = 24 hours

1 hour = 60 minutes

1 minute = 60 seconds)

Total seconds in 11.9 days =

= 11.9 d X 24 Hr X 60 min X 60 s

=1028160 Seconds.

b)

During electrolysis of MgCl₂​​ the following reaction takes place:

at cathode: Mg⁺² + 2e^- -------> Mg_(s)

at anode: 2Cl^- --------> Cl_{​​​​​2}​​​​ + 2e^-.

From the above half reactions, it is clear that, for every one mole of magnesium (24 g/mol) deposited, one mole of chlorine gas(22.4L) is liberated.

Hence,

For every 24 g /mol of Mg, 22.4 L of chlorine is released, then..

For, 655.89 g of magnesium, volume of Cl_{​​​​​2}​​​​ released is...

Volume of Cl_{​​​​​2}​​​​ = (655.89 g X 22.4L)/24 g.mol^-1.

Volume of Chlorine = 612.164 Litres.