Homework Problem 14.1

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Angela 1K
Posts: 80
Joined: Fri Sep 29, 2017 7:05 am

Homework Problem 14.1

Postby Angela 1K » Sat Mar 17, 2018 2:34 pm

The equation that we're supposed to balance is H+(aq) + Cr2O72-(aq) + C2H5OH(aq) --> Cr3+(aq) + C2H4O(aq) + H2O(l)

According to the solution manual, the balanced oxidation half-reaction should be
C2H5OH(aq) --> C2H4O(aq) + 2e- + 2H+(aq)

I'm having difficulty figuring out why there's 2 electrons added to the right-hand side when the change in oxidation states of the carbon is only -1 (from -2 to -1). From my understanding, there'd only need be 1 electron.

If someone could please explain, that'd be appreciated! Thanks

Hannah Chew 2A
Posts: 76
Joined: Fri Sep 29, 2017 7:05 am
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Re: Homework Problem 14.1

Postby Hannah Chew 2A » Sat Mar 17, 2018 2:37 pm

There's 2 carbons that undergo a change in oxidation state, so you need 2 e-. I prefer to look at it as a balance of charge. You need the 2 H+ ions on the right side to balance the hydrogens, and since the left hand side is neutral and right hand side is +2, you need to add 2e- to the right hand side to bring the net charge back to 0.

Tim Nguyen 2J
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am

Re: Homework Problem 14.1

Postby Tim Nguyen 2J » Sat Mar 17, 2018 6:30 pm

The two H atoms add a net +2 charge to the product side, so you need to add two e- to balance that out.

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