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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: sanado on May 08, 2008, 09:22:53 AM

Title: Redox?
Post by: sanado on May 08, 2008, 09:22:53 AM

What are the half equations for dichromate ions and ethanol reacting?


I have no idea, i wouldnt have guessed it wouldve been a redox unless dichromate acts as the oxidant?

Title: Re: Redox?
Post by: shelanachium on May 08, 2008, 11:38:44 AM

Is ethanal (acetaldehyde CH3CHO) the product?

Then ethanol is being oxidised thus:

CH3CH2OH --> CH3CHO + 2[H]+ + 2e-

The dichromate is acting as an oxidant by taking up these electrons. Cr is being reduced from Cr(VI) to Cr (III), so each Cr atom takes up 3 electrons. There are two Cr(VI) atoms in the dichromate ion, so this overall takes up six electrons:

[Cr2O7]2- + 6e- + 14[H]+ --> 2[Cr]3+ + 7H2O.

These are the half-reactions you asked for. As for balancing the overall equation, I leave that to you. And if the product from ethanol CH3CH2OH is ethanoic (acetic) acid CH3CO2H, see if you can construct the half-reaction for that, remembering that total charges and atoms on each side must be equal.

Title: Re: Redox?
Post by: AWK on May 09, 2008, 01:40:11 AM

Shelanahium is right concerning procedure with removing acetaldehyde from reaction mixture (temperature of reaction over boiling point of acetaldehyde), but even then some od acetaldehyde is oxidized to acetic acid.