Chemistry Electrolysis Q! Please Explain?

Question

Metallic magnesium can be made by the electrolysis of molten MgCl2.

(a) What mass of Mg is formed by passing a current of 5.90 A through molten MgCl2 for 2.20 days? in grams

(b) How many minutes are needed to plate out 14.80 g Mg from molten MgCl2, using 6.60 A of current? in minutes

Please show how to come about doing this...all my attempts keep failing terribly..

could you also please work it out..because i have no idea how to convert to faradays..i get halfway through and then i get stuck

Answer 1

You have to use Faraday's laws

so for (a)
Q=It
I=5.9
t has to be in seconds, so 2.2 x 24 x 60 x 60
t=190080

so Q = 5.9 x 190080
Q=1121472

Now use Q = n(e-) x 96500
n(e-) = 1121472/96500
n(e-) = 11.6215 mol
Since Mg needs 2 electrons per Mg ion
11.6215/2
n(Mg) = 5.8107
m(Mg) = n x Mr
m(Mg) = 5.8107 x 24.312
m(Mg) = 141.27 grams


For (b) you use the same formulas

14.80 grams Mg is 0.60875 mol
2 electons per Mg ion, therefore n(e-) = 1.2175
Q = 1.2175 x 96500
Q=117489
117489 = 6.6 x t
t = 117489/6.6
t=17801.4 seconds
t=296.7 minutes

Answer 2

1 mol Mg2+ requires 2 Faradays to convert it to Mg.

Current (A) x time (s) = charge (C)

In (a), find charge, (C), convertot Faradays, work out mol Mg, and convert to g Mg

In (b), the reasoning is similar, except that this time you need to go from g Mg to mol Mg to C, then divide by the current to get the time.

Hope this helps.

Answer 3

Electrolysis of molten salt gets sodium and chlorine, usually done using the Downs cell. Electrolysis of a solution gets hydrogen as it is not possible to have metallic sodium in water for very long!