Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: Atomic-S on 18/03/2016 04:52:30

Title: Is there a more polar liquid?
Post by: Atomic-S on 18/03/2016 04:52:30

Is there any liquid at room temperature that has greater electrical polarity of the molecule than does water?

Title: Re: Is there a more polar liquid?
Post by: evan_au on 18/03/2016 08:59:32

How about a solution of table salt (Na⁺Cl^-)?

It is 100% polarized, with complete transfer of an electron from the Sodium to the Chlorine atom.

In contrast, water merely displaces the charge slightly towards the oxygen end of the molecule, and slightly away from the hydrogen end of the molecule. (Plus, about 1 in 10 million water molecules naturally dissociates into H⁺ and OH^-, at any given moment.)

But more seriously, any chemical with two atoms having quite different electronegativity will form a polar molecule, like Hydrogen Fluoride (HF).

See: https://en.wikipedia.org/wiki/Chemical_polarity#Polar_molecules

Warning: HF is very dangerous. Do not play with this at home!

Title: Re: Is there a more polar liquid?
Post by: chiralSPO on 18/03/2016 11:43:52

Water is a fairly polar molecule, but by no means has the greatest dipole moment of common solvents. Water has a dipole moment of 1.85 D, whereas chloroform has a dipole moment of 1.08 D, but hexamethyl phosphoramide (HMPA) has a dipole moment of 5.37 D!! HMPA is no longer a common solvent due to its toxicity, and has largely been replaced by dimethylsulfoxide (DMSO), which has a dipole moment of 3.96 D.

Where water is nearly king, is in terms of dielectric constant (this table here has dielectric constant ε and dipole moment µ: http://depts.washington.edu/eooptic/linkfiles/dielectric_chart%5B1%5D.pdf)

You can see water has a dielectric constant of 80, while dmso (46.7) and hmpa (30) come up short. Formamide shows up as the winner on the table, coming in at 111!

More than a solution of salt in water, room-termperature ionic liquids are likely to be the extreme case of dipole moment: https://en.wikipedia.org/wiki/Ionic_liquid

Title: Re: Is there a more polar liquid?
Post by: Bored chemist on 19/03/2016 22:48:58

Liquid hydrogen cyanide near its melting point has a dielectric constant near 200.
But it isn't nice stuff to play with.

Title: Re: Is there a more polar liquid?
Post by: chiralSPO on 20/03/2016 13:47:33

Quote from: Bored chemist on 19/03/2016 22:48:58

Liquid hydrogen cyanide near its melting point has a dielectric constant near 200.
But it isn't nice stuff to play with.

Interesting, I did not know that, but it makes sense it would be quite high...