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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Alt+Tab on January 02, 2019, 01:00:29 AM

Title: electrodeposition olympiad acs
Post by: Alt+Tab on January 02, 2019, 01:00:29 AM

I was trying to solve it but I can not get the answer. The correct item is (B)


A 0.100-g sample of an alloy of copper and silver is dissolved in nitric acid to give a solution containing Cu2+ and Ag+ ions. This mixture is electrolyzed exhaustively to redeposit all the metal ions as the elemental metals, requiring a current of 0.150 A for 1429 s. What is the mass percent of copper in the alloy?

(A) 20.0% (B) 58.3% (C) 70.6% (D) 77.2%


mm Cu = 63,55  and Ag = 107,9
My reasoning: by finding the number of electrons produced, I use two types of logic.
1. I consider 2/3 of the electrons produced go to copper
2. All electrons produced will go to copper.
none matches  :( :(

Title: Re: electrodeposition olympiad acs
Post by: Borek on January 02, 2019, 02:40:15 AM

Quote from: Leonardo Silva on January 02, 2019, 01:00:29 AM

I use two types of logic.
1. I consider 2/3 of the electrons produced go to copper
2. All electrons produced will go to copper.

They don't produce matching result because they are both wrong. How the electrons are shared between elements depends on the Cu/Ag ratio in the original sample.

Assume there were n_Cu - number of moles of Cu, and n_Ag - number of moles of Ag. Try to express both information given in the problem using math equations and these two unknowns.