Question

1- A current of 3.59 A is passed through a Cr(NO3)2 solution for 1.30 hours. How much chromium is plated out of the solution?

2-A current of 4.87 A is passed through a Sn(NO3)2 solution. How long (in hours) would this current have to be applied to plate out 7.30 g of tin?

Answer 1

1)

Electrolysis equation is:

Cr2+ + 2e- ------> Cr

1 mol of Cr requires 2 mol of electron

1 mol of electron = 96485 C

So,1 mol of Cr requires 192970 C

let us calculate the charge passed:

t = 1.3 hr = 1.3*3600 s = 4.68*10^3 s

time, t = 4.68*10^3s

Q = I*t

= 3.59A * 4.68*10^3s

= 1.68*10^4 C

mol of Cr plated = 1.68*10^4/192970 = 8.707*10^-2 mol

Molar mass of Cr = 52 g/mol

mass of Cr = number of mol * molar mass

= 8.707*10^-2 * 52

= 4.527 g

Answer: 4.53 g

2)

Electrolysis equation is:

Sr2+ + 2e- ------> Sr

1 mol of Sr requires 2 mol of electron

1 mol of electron = 96485 C

So,1 mol of Sr requires 192970 C

let us calculate mol of element deposited:

use:

number of mol, n = mass/molar mass

= 7.3/87.62

= 8.331*10^-2 mol

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

= 8.331*10^-2*1.93*10^5

= 1.608*10^4 C

use:

time = Q/i

= 1.608*10^4/4.87

= 3.301*10^3 seconds

= 3.301*10^3/60 min

= 55.02 min

= 55.02/60 hr

= 0.917 hr

Answer: 0.917 hr