Homework Help: Electrochemistry II. Electrolsis

1. Apr 19, 2006

david2120

what mass of copper could be electroplated on the cathode in an experiment where an average of 200 mA was passed through the cell for 35 mins?

I don't understand the question? how do you figure the mass out? I know that copper is 63.55g/mole but do i mutiple it by 200mA and 35 mins?

2. Apr 19, 2006

durt

You can figure out the total charge that reaches the cathode, and from there consider the reduction reaction.

3. Apr 19, 2006

david2120

200mA x 2100secs divide 1000mA = 420 coulombs

I am doing in right so far and what do I do next? How do I find what mass of copper could be electroplated on the cathode?

4. Apr 19, 2006

Gokul43201

Staff Emeritus
Again, we have an incomplete question. Is there no reference to the electrolyte used ? The answer will vary depending on whether the electrolyte has Cu+ ions or Cu2+ ions. In the absence of further information, assume it's Cu2+ and proceed.

What you've done is correct so far. Now, what is the purpose of transfering this charge - what does it do to the ions in the electrolyte ?

5. Apr 20, 2006

david2120

2 moles of electrons to produce one mole of copper because the equation is Cu2+(aq) + 2e ------> Cu(s) i know Cu is 63.55g/mole but that's all the info I have

6. Apr 20, 2006

Gokul43201

Staff Emeritus
Was the equation given to you as part of the question ?

7. Apr 20, 2006

david2120

no I got it from the experiment we did in trying to determine Faraday's constant the question is a postlab question. I weighted the copper strips which was 16.57 and 19.051 and lowered to 16.563 and 19.014 after the experiment was done but I don't know am supposed to use those numbers cause the average current i got was 9.0745x10^-2 and in the post question it says average of 200 mA

8. Apr 20, 2006

Gokul43201

Staff Emeritus
I'm going to ignore the numbers you got in your lab and help you only with the postlab question. But henceforth, please provide all the information that comes with the question.

So far, you've got the total charge, Q = I*t (in Coulombs)

Do you see a way of going from the total charge transferred to the number of moles of Cu deposited ? Remember, it takes two moles of electrons to deposit one mole of Cu.