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2002 - Multiple Choice - Q18 - HSN forum

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2002 - Multiple Choice - Q18


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#1 david__taylor

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Posted 27 May 2005 - 01:07 PM

I'm stuck as to how you find out if a reaction is reduction or not. This is the one I got stuck on:

Which reaction can be classified as reduction? (Note: I couldn't get small numbers).

A. CH3CH2OH --> CH3COOH

B. CH3CH(OH)CH3 --> CH3COCH3

C. CH3CH2COCH3 --> CH3CH2CH(OH)CH3

D. CH3CH2CHO --> CH3CH2COOH

At first I found out what was missing from each reaction, ie, for A. 2 Hydrogens have been lost and 1 Oxygen added in. At the end I chose answer D as 1 Oxygen had been gained (reduction is Gain of electrons) so I thought it would be gaining electrons by gaining an oxygen. Obviously that's wrong, the answer is C in which 4 Hydrogens have been gained.

How is C reduction?

#2 dfx

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Posted 27 May 2005 - 01:14 PM

In hydrocarbons reduction/oxidation is a change in the Oxygen to Hydrogen ratio. I can't recall whether a bigger/smaller ration and what with respect to what it is, but I remember seeing it on the HSN chemistry notes for Unit 2. I'm pretty sure its to do with that smile.gif

#3 david__taylor

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Posted 27 May 2005 - 01:15 PM

Kl Thanks, I'll check them out then.

#4 werlop

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Posted 27 May 2005 - 01:28 PM

Oxidation - increase in the O:H ratio (which also can be seen as a decrease in the H:O ratio.

Reduction - decrease in the O:H ratio, or increase in the H:O ratio.

C is reduction because the number of oxygen atoms has remained constant while more hydrogen atoms have been added, so the H:O ratio has increased.


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#5 david__taylor

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Posted 27 May 2005 - 01:41 PM

thanks werlop and dfx. i understand now.





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