6th Edition, 14.1  [ENDORSED]

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Hai-Lin Yeh 1J
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6th Edition, 14.1

Postby Hai-Lin Yeh 1J » Wed Feb 27, 2019 7:32 pm

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in the blood:
H+ (aq) + Cr2O7 2- (aq) + C2H5OH (aq) -> Cr3+ (aq) + C2H4O (aq) + H2O (l)
(a) Identify the elements undergoing changes in oxidation state and indicate the initial and final oxidation numbers for these elements.

Can someone explain how we know C is oxidized from 2- to 1-?

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Re: 6th Edition, 14.1  [ENDORSED]

Postby Chem_Mod » Wed Feb 27, 2019 7:39 pm

Sure! Let's look at the breakdown of the oxidation numbers. We know that H has an oxidation number of +1, and oxygen is usually (-2). As such, C2H5OH has a -2 from Oxygen and a +6 from Hydrogen, with an overall +4. To produce the neutral charge on the molecule, C must balance this out. There are 2 carbons, meaning the -4 is divided by 2 and split between them. Hence, -2 charge. Try following this same method for the second molecule.

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