Question

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

Part A

What mass of Mg is formed by passing a current of 4.00 A through molten MgCl2 for 4.70 days?

Express your answer using three significant figures.

Part B

How many minutes are needed to plate out 26.00 g Mg from molten MgCl2, using 2.90 A of current?

Express your answer using three significant figures.

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 = 4.7 days = 4.7*24*3600 s = 4.061*10^5 s

time, t = 4.061*10^5s

Q = I*t

= 4A * 4.061*10^5s

= 1.624*10^6 C

mol of Mg plated = 1.624*10^6/192970 = 8.417 mol

Molar mass of Mg = 24.31 g/mol

mass of Mg = number of mol * molar mass

= 8.417 * 24.31

= 2.046*10^2 g

Answer: 205 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

= 26/24.31

= 1.07 mol

total charge = mol of element deposited * charge required for 1 mol

= 1.07*1.93*10^5

= 2.064*10^5 C

use:

time = Q/i

= 2.064*10^5/2.9

= 7.117*10^4 seconds

= 7.117*10^4/60 min

= 1.19*10^3 min

Answer: 1.19*10^3 min