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Jasmine 2C
Posts: 184
Joined: Wed Sep 18, 2019 12:18 am


Postby Jasmine 2C » Mon Feb 24, 2020 10:27 pm

This is probably one of the easiest redox questions but I don't understand redox overall (with the balancing, half-rxns, etc) :( can someone explain how to do this?

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in blood:
H1 (aq) + Cr2O722 (aq) + C2H5OH (aq) -> Cr31 (aq) + C2H4O (aq) + H2O (l)
Identify the elements undergoing oxidation or reduction and indicate their initial and final oxidation numbers. (b) Write and balance the oxidation half-reaction. (c) Write and balance the reduction half-reaction. (d) Combine the half-reactions to produce a balanced redox equation.

Jessa Maheras 4F
Posts: 121
Joined: Fri Aug 02, 2019 12:16 am

Re: 6K1

Postby Jessa Maheras 4F » Tue Feb 25, 2020 9:54 am

Hi Jasmine! FIrst, I found Dr. Lavelle's walkthrough on balancing redox runs very helpful, you can fin these in a recent email of his. But, he doesn't include how to figure out Oxidation #'s, which is necessary to start the problem. Figure out the oxidation #'s: O and H have #'s that stay the same, but you see that C and Cr both have numbers that change. In oder to find this, add up charges of +1 for H and -2 for O, then see what charge will counteract those to get the net charge of the molecule indicated (neutral for these). Then, follow the steps for dividing up the half run and balancing them!

Kassidy Ford 1I
Posts: 103
Joined: Sat Aug 17, 2019 12:16 am
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Re: 6K1

Postby Kassidy Ford 1I » Tue Feb 25, 2020 12:26 pm

^^ because this reaction is in acidic solution, for each half reaction balance excess oxygen with H2O and then add H+ to the other side to balance excess H+. Then use electrons to make sure the charges are balanced.

Brianna Becerra 1B
Posts: 117
Joined: Fri Aug 02, 2019 12:16 am

Re: 6K1

Postby Brianna Becerra 1B » Tue Feb 25, 2020 12:44 pm

Some basic oxidation numbers which are used commonly and will help you figure out which is the reduction/oxidation is that typically, 0=2- and H=1+. Knowing these can help you figure out the oxidation number of another element being used with them when considering what value combination would make up the overall given charge.

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