How long will it take the zinc to reach the desired thickness?

1. Apr 5, 2009

rayhan619

1. The problem statement, all variables and given/known data

For a science experiment you need to electroplate a 130 nm thick zinc coating onto both sides of a very thin, 3.0 cm*3.0 cm copper sheet. You know that the charge carriers in the ionic solution are divalent (charge 2e) zinc ions. The density of zinc is 7140 kg/m^3
If the electroplating apparatus operates at 1.3 mA, how long will it take the zinc to reach the desired thickness?

2. Relevant equations

3. The attempt at a solution

we know area and thickness of the plate and the density of the zinc, and the current.
so we can get the volume of the plate and using density we can figure out the mass.
volume = 3*10^-2* 3*10^-2* 130*10^-9 m = 1.17*10^-10 m^3
and the mass = 1.17*10^-12 m^3 * 7140 kg/m^3 = 8.35*10^-7 kg
in 1 mole the weight of zinc is 65.38 g
so in 8.35*10^-7 kg 1.3*10^-8 mole
1 mole we have 6.022*10^23 atoms
so in 1.3*10^-8 mole we have 1.3*10^-8 * 6.022*10^23 = 7.83*10^15 atoms
so number of electrons = 7.83*10^15 *2 = 1.57*10^16
1 Coulomb is equal to 6.241*10^18 electrons.
so 1.57*10^16 electron = 2.5*10^-3 C
I = Q/t
so t = Q/I
= 2.5*10^-3/1.3*10^-3
= 1.92 s
so for both side the total time would be 1.92*2 = 3.84 s

i tried plugging that number but apparently it was wrong.
Any ideas what i am doing wrong in here?
Any help would be appreciated.

2. Apr 5, 2009

Redbelly98

Staff Emeritus
Re: Electroplating

Check the units, both kg and g appear here. Use one or the other.

3. Apr 5, 2009

rayhan619

Re: Electroplating

yes you are right.
i redo the part.
does it look good?

in 1 mole the weight of zinc is 65.38 g
so in 8.35*10^-7 kg 1.3*10^-5 mole
1 mole we have 6.022*10^23 atoms
so in 1.3*10^-5 mole we have 1.3*10^-5 * 6.022*10^23 = 7.83*10^18 atoms
so number of electrons = 7.83*10^18 *2 = 1.57*10^19
1 Coulomb is equal to 6.241*10^18 electrons.
so 1.57*10^19 electron = 2.5 C
I = Q/t
so t = Q/I
= 2.5/1.3*10^-3
= 1923 s
so for both side the total time would be 1923*2 = 3846 s

4. Apr 5, 2009

Redbelly98

Staff Emeritus
Re: Electroplating

Looks good! Just watch the sig figs.

5. Apr 5, 2009

rayhan619

Re: Electroplating

i tried putting 3.8*10^3 s
but that didnt work either.
donno whats wrong with this problem. : (