Question

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

Metallic magnesium can be made by the electrolysis of molten MgCl2. (a) What mass of Mg is formed by passing a current of 5.08 A through molten MgCl2 for 1.40 days? The unbalanced chemical reaction representing this electrolysis is shown below. MgCl2 → Mg + Cl2 g of Mg is formed by this electrolysis. (b) How many minutes are needed to plate out 16.00 g of Mg from molten MgCl2 using 6.48 A current? minutes are needed.

Answer 1

a)
Electrolysis equation is:
Mg2+   +   2e-    ------> Mg

1 mol of Mg requires 2 mol of electron
1 mol of electron = 96485 C
So,1 mol of Mg requires 192970 C

let us calculate the charge passed:
t = 1.4 days = 1.4*24*3600 s = 1.21*10^5 s

time, t = 1.21*10^5s

Q = I*t
= 5.08A * 1.21*10^5s
= 6.145*10^5 C

mol of Mg plated = 6.145*10^5/192970 = 3.184 mol
Molar mass of Mg = 24.31 g/mol

mass of Mg = number of mol * molar mass
= 3.184 * 24.31
= 77.41 g
Answer: 77.4 g

b)
Electrolysis equation is:
Mg2+   +   2e-    ------> Mg

1 mol of Mg requires 2 mol of electron
1 mol of electron = 96485 C
So,1 mol of Mg requires 192970 C

let us calculate mol of element deposited:

molar mass of Mg = 24.31 g/mol
use:
number of mol of Mg, n = mass of Mg/molar mass of Mg
= 16/24.31
= 0.6582 mol


total charge = mol of element deposited * charge required for 1 mol
= 0.6582*1.93*10^5
= 1.27*10^5 C
use:
time = Q/i
= 1.27*10^5/6.48
= 1.96*10^4 seconds
= 1.96*10^4/60 min
= 327 min
Answer: 327 min