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Topic: Just got a test back (Electro Chemistry), and want to confirm something.  (Read 4091 times)

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Offline kakashi

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Just got a test back (Electro Chemistry), and want to confirm something.
« on: December 12, 2012, 07:49:14 PM »
I had to identify all the oxidation numbers in a compound, and was given a structural diagram. This is what it looked like:



For the oxidation number, on the first Carbon (on the left), I gave it +2. Then for all the Oxygens, I gave them -2, and +1 for all the Hydrogens. I gave the second Carbon (on the right) an oxidation number of 0.

I got the oxidation numbers for both Carbons wrong. Can someone explain to my why this is so? And what the correct ones would be?
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Offline ethan1990

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Re: Just got a test back (Electro Chemistry), and want to confirm something.
« Reply #1 on: December 12, 2012, 08:06:27 PM »
The correct answer for the left carbon should be -2. Each hydrogen decreases the oxidation number by one, and the one oxygen increases it by one. -3 + 1 = -2.

For the other one, the correct answer is +3, as each oxygen increases the carbon's oxidation number by one.

If you have any questions, feel free to reply.
Best of luck in the future.
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Offline kakashi

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Re: Just got a test back (Electro Chemistry), and want to confirm something.
« Reply #2 on: December 12, 2012, 08:22:16 PM »
Hey. Thanks for replying.

Isn't Carbon more electronegative than Hydrogen? I thought that it would take an electron from each Hydrogen, and become +3, and then lose 1 electron to Oxygen, which is more electronegative than Carbon, making it +2? For the second Carbon, since it's only bonded to Oxygen, Oxygen takes all the electrons, so it goes from +4 to 0.

Our teacher said to assume that the more electronegative element takes all the electrons in the covalent bonds, when attempting to identify the oxidation numbers.
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Offline Borek

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Re: Just got a test back (Electro Chemistry), and want to confirm something.
« Reply #3 on: December 13, 2012, 03:29:35 AM »
Quote from: kakashi on December 12, 2012, 08:22:16 PM
Isn't Carbon more electronegative than Hydrogen? I thought that it would take an electron from each Hydrogen, and become +3

If carbon is +3, hydrogens can't be +1, which is what you started with.
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Offline Hunter2

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Re: Just got a test back (Electro Chemistry), and want to confirm something.
« Reply #4 on: December 13, 2012, 05:12:37 AM »
Quote
For the other one, the correct answer is +3, as each oxygen increases the carbon's oxidation number by one.

One Oxygen has double bond and so the carbon has to be +4
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Offline kakashi

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Re: Just got a test back (Electro Chemistry), and want to confirm something.
« Reply #5 on: December 13, 2012, 08:54:35 PM »
Guys, I think I've lost a LOT of brain cells. I can't believe I forgot that as electrons are added, the charge becomes negative. Based on this, the oxidation number of the first carbon would be -2, and the second one would be +4. These answers are correct, because I've confirmed them with my teacher.

Thanks a lot for your *delete me*
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