6th Edition, 14.1  [ENDORSED]

Moderators: Chem_Mod, Chem_Admin

Hai-Lin Yeh 1J
Posts: 89
Joined: Fri Sep 28, 2018 12:16 am
Been upvoted: 1 time

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-?

Posts: 19198
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 837 times

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.

Return to “Balancing Redox Reactions”

Who is online

Users browsing this forum: No registered users and 1 guest