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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Mrbazoun on September 24, 2010, 02:02:51 PM

Title: Why Does H20 Have a Higher BP than CH3OH?
Post by: Mrbazoun on September 24, 2010, 02:02:51 PM

Hi I'm in Organic Chemistry. ::)

My answer to this question was that H20 forms 2 H-bonds when CH3OH can only form 1.

Another Q:Why  is h20's BP higher than NH3? I answered because H20 is more polar because there is a great electro-negativity difference between O and H.

One I'm stuck on: Why does H20 have a higher BP than HF??

Thank you!!

Title: Re: Why Does H20 Have a Higher BP than CH3OH?
Post by: nj_bartel on September 24, 2010, 04:26:07 PM

The first one is correct. The second one is partially correct. There's a difference in the extent of h bonding for the two as well

Title: Re: Why Does H20 Have a Higher BP than CH3OH?
Post by: igloo5080 on September 25, 2010, 12:43:39 PM

The most important property to consider when estimating the strength of a hydrogen bond is indeed the difference in electronegativities between H and N, H and O and H and F.

Another very important consideration is to realize that hydrogen bonds involve the hydrogen atom of one molecule and a lone pair of electrons on the N, O or F of another molecule. Thus you need to consider the number of hydrogen atoms in a molecule as well as the number of lone pairs of electrons on the attached atom (N, O or F). This will lead you to predict the extent of hydrogen bonding possible within a substance.

Apply both of these ideas to NH₃, H₂O and HF, and all should come clear.