Kaplan Electrochemistry Topical Test

[Tracy47]

Hi, did anyone have problem with this topicals? I am having the hardest time with electrochemistry, and find this topical impossible, especially with passage 2, with the two electrolytic cells, where you have to figure out which half reactions occur at each electrode, given only the battery voltage, and 5 different half reactions with its reduction potentials. Does anyone know how to figure this out? Please help!

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[gotgame83]

I took that test last week, it wasnt pretty. If you need to know how to figure it out send me a PM and ill send ya the detailed answers.

 

[DrChandy]

Hi, did anyone have problem with this topicals? I am having the hardest time with electrochemistry, and find this topical impossible, especially with passage 2, with the two electrolytic cells, where you have to figure out which half reactions occur at each electrode, given only the battery voltage, and 5 different half reactions with its reduction potentials. Does anyone know how to figure this out? Please help!

I do not have access to the specific problem, but here's how to solve such problems:

Memorize the formula Ecell=cathode-anode (Ecell=battery voltage)

Using the half reactions, figure out which has the E value (aka reduction potential) that is the highest in relation to the others. This highest value half reaction is the species that is reduced (cathode value).

Using the above formula, substitute battery voltage for Ecell, and the obtained half reaction E value for the cathode. (Do not change any of the E value signs from the pertinent half reactions when substituting their values into the equation Ecell=cathode-anode).

Solve for the unknown to get the anode half reaction E value.

 

[Dr Gerrard]

I had the same problem as the first poster. How can you tell what gets reduced/oxidized where? This is talking about passage 2.

For example, why doesn't sulfate get oxidized at electrode 2? It would have a less negative potential then the oxygen reaction, but still, the latter is the one that gets oxidized.

Also, do the protons get reduced rather than the sodium because of the very large difference in potential? Why doesn't this difference also work for electrode 2?