#76 on PS 7R

[sans005]

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Hi, I dont understand the following question: (#76 on 7R-PS)
Approximately how many moles of Al3+ are reduced when 0.1 faraday of charge passes through a cell during the production of Al? (Note: Assume there is excess Al3+ available and that Al3+ is reduced to Al metal only.)
1) 0.033
2) 0.050
3) 0.067
4) 0.10
ans: 0.033
The explanation is so simple and I understand every other q in gen chem, but can't understand this one. Please anyone have an explanation?

 

[Wertt]

Hi, I dont understand the following question: (#76 on 7R-PS)
Approximately how many moles of Al3+ are reduced when 0.1 faraday of charge passes through a cell during the production of Al? (Note: Assume there is excess Al3+ available and that Al3+ is reduced to Al metal only.)
1) 0.033
2) 0.050
3) 0.067
4) 0.10
ans: 0.033
The explanation is so simple and I understand every other q in gen chem, but can't understand this one. Please anyone have an explanation?

Basically it is asking how many electrons you have accumulated and how much aluminum 3+ you can reduce with those electrons. The key is to realize that one Faraday of charge is 96,500 Coulombs, and that this corresponds to the charge on a mole of electrons. So, 0.1 F is 0.1 mole of electrons. How many moles of al 3 can you reduce with 0.1 moles of electrons? well, you need three e for each Al atom, so 0.033.

 

[sans005]

hey, THANKS. I was trying to think along that way...but it was very forced. I didnt understand the logic..now i do. thanks again. 👍 you guys are the best.