Ethanol as a solvent (1 Viewer)

[sooki0326]

Hi, I'm having trouble with the idea how one part of ethanol can be polar whilst the other is non polar. In my mid course, I got a queston that said explain this with diagrams and I had no idea but my teacher gave me a diagram showing how the oxygen is delta minus, hydrogen is delta plus and the carbon is delta plus. People say that OH is polar but if C was delta plus, wouldn't that make the CH3CH2 part polar as well? Really confused lol

 

[x jiim]

The -OH end is polar because of the different electronegativities of the O and H atoms. The oxygen is more electronegative so in the covalent bond it tends to hog the electrons, meaning that it has a slight negative charge and the hydrogen has a slight positive charge.

The CH3CH2 part isn't polar as there isn't a big enough difference in the electronegativities of carbon and hydrogen for this to happen.

If that makes sense? =\

 

[adomad]

The CH3CH2 part isn't polar as there isn't a big enough difference in the electronegativities of carbon and hydrogen for this to happen.

If that makes sense? =\

its because the net dipole = 0... all the vectors cancel out

 

[sooki0326]

Yes I understand that the OH is polar due to the difference between electronegativity but my teacher also wrote on the diagram that the C with the OH on it is slightly positive. Is this true ?

 

[x jiim]

I think the C-O bond was polar too.. something about that being why alkanoic acids have higher MP/BP? But I don't think you need to need to know that with regards to ethanol, because it's mainly the O-H bond that's polar, and the point is that it has a polar and a non-polar end =\

 

[adomad]

This is a simplistic and ill-explained description. The reason Ethanol is considered to have both a polar and non-polar end is because the OH bond is slightly polar due to the relatively large difference in electronegativity between O and H. The electronegativities of C and H are sufficiently similar that the the bond is considered non-polar covalent. Thus, consider the OH group to be polar, as opposed to the entire molecule being polar.

I think this is right...

its not simplified.... think of the molecule carbon dioxide... non-polar as it exists as a gas (weak intra-molecular forces)... its O=C=O ... in this case the oxygen is more(not similar) electronegative where the electronegativity of oxygen is 3.6 and for carbon it is 2.5... the two vectors point outwards, cancelling each other out

with the non-polar tail, the H-H2C-H2C- , the carbon is more electronegative 0.2 units hence one vector points up and the other points down, effectively cancelling each other out. same with the other H2C. with the one on the side, you have that adding to the C-O vector, making c-o a electronegative section as well...

 

[thongetsu]

If you're having trouble with this then you are going to really need help.

 

[adomad]

I have no idea what you are saying. Diagram perhaps? The C-O bond is a polar bond, which is the important detail in this case. Also remember that the C-H end is the non-polar end.

.http://www.glowfoto.com/static_image/02-183431L/9016/jpg/05/2010/img6/glowfoto