Question

Semimetallic silicon can be made by the electrolysis of molten SiO₂.

(a) What mass of Si is formed by passing a current of 6.24 A through molten SiO₂ for 2.10 days? The unbalanced chemical reaction representing this electrolysis is shown below.

SiO₂ Si + O₂

g of Si is formed by this electrolysis.







(b) How many minutes are needed to plate out 13.00 g of Si from molten SiO₂ using 7.92 A current?


minutes are needed.

Answer 1

a)
Electrolysis equation is:
Si4+   +   4e-    ------> Si

1 mol of Si requires 4 mol of electron
1 mol of electron = 96485 C
So,1 mol of Si requires 385940 C

let us calculate the charge passed:
t = 2.1 days = 2.1*24*3600 s = 1.814*10^5 s

time, t = 1.814*10^5s

Q = I*t
= 6.24A * 1.814*10^5s
= 1.132*10^6 C

mol of Si plated = 1.132*10^6/385940 = 2.934 mol
Molar mass of Si = 28.09 g/mol

mass of Si = number of mol * molar mass
= 2.934 * 28.09
= 82.4 g
Answer: 82.4 g

b)
Electrolysis equation is:
Si4+   +   4e-    ------> Si

1 mol of Si requires 4 mol of electron
1 mol of electron = 96485 C
So,1 mol of Si requires 385940 C

let us calculate mol of element deposited:

molar mass of Si = 28.09 g/mol
use:
number of mol of Si, n = mass of Si/molar mass of Si
= 13/28.09
= 0.4628 mol


total charge = mol of element deposited * charge required for 1 mol
= 0.4628*3.859*10^5
= 1.786*10^5 C
use:
time = Q/i
= 1.786*10^5/7.92
= 2.255*10^4 seconds
= 2.255*10^4/60 min
= 376 min
Answer: 376 min