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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: spoudyal3 on January 12, 2006, 09:43:30 PM

Title: H bonding of H2O2
Post by: spoudyal3 on January 12, 2006, 09:43:30 PM

I do not know what molecule would have a higher melting point, H2O2 or HF (actually H2S was in the problem as well but I automatically discarded it). Both exhibit H bonding and yes the H-F bond is stronger than an H-O bond, however, the structure of H2O2 H-O-O-H is throwing me off. I asked my teacher and she was not absolutely sure either since it could be either:

H               or   H     H
  \                     \    /
   O-O                O-O
         \
         H

and it all depends on whether the two hydrogen are on the same plane or not. My initial thought was that the geometry of H2O2 was like the first one but I am not absolutely sure (my teacher thinks it may be the second one but does not care about it so much because it was not asked on the homework).

Please tell me if you have a difinitive answer to the question. Thank you.

-Sid

Title: Re:H bonding of H2O2
Post by: mike on January 12, 2006, 09:50:03 PM

Try google search of H2O2 images. I doubt the two H would be in the same plane, and the two ways you have drawn H2O2 could actually both be the same as it doesn't really show the geometry. Good luck :)

Title: Re:H bonding of H2O2
Post by: spoudyal3 on January 12, 2006, 09:55:03 PM

Thanks. That was a good idea and I probably should have thought of that.
I found all of them with H on a different plane but I am not completely sure if this really means that H2O2 has stronger forces than HF. Also I am not positive why it would mean it would have stronger forces. Please clarify this for me.
Thanks again.

-Sid

Title: Re:H bonding of H2O2
Post by: mike on January 13, 2006, 01:11:10 AM

I am not entirely sure why the plane of the hydrogens makes such a difference. And I don't know which has the higher melting point. But I would guess that hydrogen peroxide could make twice as many hydrogen bonds per molecule as HF because it has two oxygens and two hydrogens.

Do you actually know the melting points of these compounds? I haven't seen them as solids myself.

Title: Re:H bonding of H2O2
Post by: AWK on January 13, 2006, 02:51:20 AM

It is assumed H2O2 in solution shows a torsion angle 180 degree, but in a solid state this torsion angle (H-O-O-H) is 111 degree. All melting points of these compounds uoy can find here: http://www.fsref.com/Fatal/FE110701.php