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Topic: Non-Polar dissolves Non-polar?  (Read 48513 times)

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Offline chuckface

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Non-Polar dissolves Non-polar?
« on: October 31, 2009, 10:33:30 PM »
Why is it that non-polar substances will dissolve other non-polar substances? example: non-polar petroleum stored in a non-polar polethylene milk carton and the milk carton will eventually start to disintergrate. Our chemistry teacher has suggested it is something to do with the temporary dipoles interacting with other temporary dipoles and forming a 'sigma' of forces and therefore a relativly strong interaction. Is this correct? agree/disagree?

Thanks in advance anyone! :)

Offline Ranadeep

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Re: Non-Polar dissolves Non-polar?
« Reply #1 on: November 01, 2009, 12:19:20 AM »
There will be Induced Dipole Dipole Interactions also called "London Dispersion Forces"between the molecules of Non Polar Compounds . This is caused by Instantaneous Dipoles created in non polar molecule
Suppose take some small Molecule ( Non polar ) or at least a He Atom ..at a particular instant The electrons of the atom for ex.are left side .. i mean the electrons revolve round the nucleus and suppose they are at left side of atom at some particular instant. Then There will be Very small Negative Charge Developed on the left side and Very Small Positive charge on right side .. Now Consider this Atom goes near another atom ..The first atom we took ie, the charged atom(partially) induces the dipole creating Dipoles on its near by atoms or(molecules ) See the resource down for diagrammatic : )

This can be understood by ...ex you take H-Cl which is Polarized  ...+     ...-
                                                                                      H  ----Cl      
                                                                                        : ..-          :.. +  
                                                                                           C ======C 
when brought near ethene(almost Non Polar) is polarized like the above : )
Resource : http://www.chem.purdue.edu/gchelp/liquids/inddip.html

But guys i dont understand one thing why cant this Nonpolar substances Dissolve in Polar  Solvents ? There could be some Attraction bettwen Polar charges of Polar molecule and This Instantenous dipoles of this Non Polar Molecule .. so why its not possible ?

Thanks in Advance : )
I am 15 from India and i like doing chemistry

Offline chuckface

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Re: Non-Polar dissolves Non-polar?
« Reply #2 on: November 01, 2009, 05:49:31 AM »
Thanks Ranadeep!

I also wondered about your last point... so thanks from me too anyone!

Offline Dan

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Re: Non-Polar dissolves Non-polar?
« Reply #3 on: November 01, 2009, 07:50:01 AM »
If you consider a polar solvent (P), with strong dipole-dipole interactions (permanent dipoles rather than induced), the molecules are quite happy experiencing these favourable interactions (P-P).

If you add a non-polar species (N) into the mix we now have to consider the interactions between the non-polar additive and the polar solvent (N-P).

The coulombic interactions for N-P will be far weaker than P-P, so it is more energetically favourable for a P to interact with a P than a P to interact with an N. What this basically means is that N is getting in the way and disrupting the favourable P-P interactions. If the N-P interaction is very low compared to the P-P interaction, the dissolving process will be too energetically unfavourable (because you are losing P-P interactions) and the mixture will remain heterogeneous.

If the P-P interaction is similar to the N-P interaction this is not a problem - this is why "like dissolves like"

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Offline Ranadeep

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Re: Non-Polar dissolves Non-polar?
« Reply #4 on: November 01, 2009, 10:25:09 AM »
Thanks for the Reply .. Very nice Explanation  :) ..
I am 15 from India and i like doing chemistry

Offline chuckface

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Re: Non-Polar dissolves Non-polar?
« Reply #5 on: November 02, 2009, 03:21:57 AM »
thankyou so much! ;D

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