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Which substance would be expected to exhibit the greatest surface tension at 25 ˚C?...

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lak-86 | Student, Undergraduate | Salutatorian

Posted August 18, 2013 at 9:52 AM via web

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Which substance would be expected to exhibit the greatest surface tension at 25 ˚C?

(A) CH3OCH3

(B) C2H5OH
(C) CH3CH(OH)CH3

(D) CH2(OH)CH2OH

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mvcdc | Student , Undergraduate | (Level 1) Associate Educator

Posted August 18, 2013 at 10:01 AM (Answer #1)

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Surface tension is the tendency of a liquid surface to be pulled inwards due to the difference between the force of attraction involved in exterior molecules or molecules at the surface from the interior or bulk molecules. 

Since it is brough upon by the attraction of molecules, a higher surface tension would be expected from a liquid that has a higher net polarity, and hence the higher tendency to attract each other -- stronger intermolecular forces. Non-polar molecules would have a lower suface tension than polar substances.

All given compounds are polar. However, only three are capable of forming the more stronger hydrogen bonds (B-D). Among these, ethylene glycol is capable of forming more hydrogen bonds, and hence it has stronger intermolecular forces (since it has two hydroxyl groups). 

Ethylene glycol (letter D) will have the greatest surface tension.

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