Chemistry Problem

[sehri1234]

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Can someone please how to do this problem ? (TPR problem)

Cu - Anode electrode
Zn - Cathode electrode

A current of 2 amps is sustained for 16 minutes. what mass of Cu(s) is deposited on the zinc electrode? (Faradays' constant: 96500 C/mol e-)

 

[leonardoson]

Remember current is Coulombs per Unit time (C/S). Multiply the 2 amps by (16 mins x 60 Secs). You are then left with the amount of charge that moves during that time in the units of Coulombs. Now divide by faraday's constant to get moles of electrons. You should also know how many moles electrons are transferred per mole of Cu, this depends on the Cu Ion you are working with. I imagine they give you the redox equations or electrochemical equations. Divide the total amount of moles electrons by moles electrons transferred per mole of Cu to get moles of Cu(s). You should be able to figure it out from there.

Btw if someone else sees this and I have made a mistake, please correct me. I didn't do this on paper which would make it easier to see my work.

 

[theonlytycrane]

^ is correct 🙂 Just clarifying for OP:

Cu at the anode will be oxidized. Likely Cu -> Cu(2+) + 2e-.

I = Q / deltaT. I = 2 amps and deltaT = 16 minutes (convert to seconds). The units of Q is Coulombs.

Use the Coulombs from above and convert to mol e- using the conversion factor given 1 mol e- / 96500 C. 2 mol e- are needed per mol Cu -> find mass of Cu(s).

 

[BerkReviewTeach]

Remember current is Coulombs per Unit time (C/S). Multiply the 2 amps by (16 mins x 60 Secs). You are then left with the amount of charge that moves during that time in the units of Coulombs. Now divide by faraday's constant to get moles of electrons. You should also know how many moles electrons are transferred per mole of Cu, this depends on the Cu Ion you are working with. I imagine they give you the redox equations or electrochemical equations. Divide the total amount of moles electrons by moles electrons transferred per mole of Cu to get moles of Cu(s). You should be able to figure it out from there.

Btw if someone else sees this and I have made a mistake, please correct me. I didn't do this on paper which would make it easier to see my work.

Your explanation of how to solve it is great. It takes 2 electrons to reduce Cu2+ to Cu, so you need to account for that (as you suggested people make sure to consider). Where there may be a problem is most likely the OP's depiction of the question. If it's electrolytic (as implied by a Cu anode and Zn cathode), then Cu is actually being oxidized and it will not be deposited at all. Additionally, it would not ever be deposited on Zinc if the half cells are separated.

 

[premedkid1994]

All Teachers/never Fail = me
🙂

 

[leonardoson]

Your explanation of how to solve it is great. It takes 2 electrons to reduce Cu2+ to Cu, so you need to account for that (as you suggested people make sure to consider). Where there may be a problem is most likely the OP's depiction of the question. If it's electrolytic (as implied by a Cu anode and Zn cathode), then Cu is actually being oxidized and it will not be deposited at all. Additionally, it would not ever be deposited on Zinc if the half cells are separated.

THANK YOU!! This bothered me. I didn't know if it was a typo by the OP or someone writing the question knew more chemistry than I did. I've only taken gen chem. This would imply that the actual CU atoms would transfer over to the zinc electrode, which is something my teacher stressed doesn't happen.

 

[BerkReviewTeach]

THANK YOU!! This bothered me. I didn't know if it was a typo by the OP or someone writing the question knew more chemistry than I did. I've only taken gen chem. This would imply that the actual CU atoms would transfer over to the zinc electrode, which is something my teacher stressed doesn't happen.

Your teacher is right (and spot on in stressing that fact). I assume it's a typo by the OP.