Question

When electricity (the flow of electrons) is passed through a solution, it causes an oxidation-reduction (redox) reaction to occur. If the solution contains a metal cation such as Ag+, the flow of electrons will reduce the silver ion, causing solid silver to plate onto the electrode. The amount of metal plated depends on the number of electrons passed.

The total charge of a mole of electrons is 96,485 coulombs (C) and

1ampere(A)=1coulomb/second(C/s)

A) What mass of Cu(s) is electroplated by running 27.0 A of current through a Cu2+(aq) solution for 4.00 h?

B) How many minutes will it take to electroplate 34.1 g of gold by running 5.00 A of current through a solution of Au+(aq)?

Answer 1

A)

Electrolysis equation is:

Cu2+ + 2e- ------> Cu

1 mol of Cu requires 2 mol of electron

1 mol of electron = 96485 C

So,1 mol of Cu requires 192970 C

let us calculate the charge passed:

t = 4.0 hr = 4.0*3600 s = 1.44*10^4 s

time, t = 1.44*10^4s

Q = I*t

= 27A * 1.44*10^4s

= 3.888*10^5 C

mol of Cu plated = 3.888*10^5/192970 = 2.015 mol

Molar mass of Cu = 63.55 g/mol

mass of Cu = number of mol * molar mass

= 2.015 * 63.55

= 128 g

Answer: 128 g

B)

Electrolysis equation is:

Au1+ + 1e- ------> Au

1 mol of Au requires 1 mol of electron

1 mol of electron = 96485 C

So,1 mol of Au requires 96485 C

let us calculate mol of element deposited:

use:

number of mol, n = mass/molar mass

= 34.1/1.97*10^2

= 0.1731 mol

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

= 0.1731*9.649*10^4

= 1.67*10^4 C

use:

time = Q/i

= 1.67*10^4/5

= 3.34*10^3 seconds

= 3.34*10^3/60 min

= 55.67 min

Answer: 55.7 min