Chemistry - What properties does a solvent with a high dielectric constant have?
Solution 1:
Before I start, please note that I am not a chemist so be sure to verify what I say...
The electric conductivity of water depends on what is dissolved in it. For example, salt water will be far more conductive than distilled water. So if you're professor was talking about sea water, the answer could actually be different from purified water.
Due to the dissolved salt ions, sea water is a better conductor of electricity and so by definition it will be a poor dielectric, since according to this Wikipedia article: to be a good dielectric a substance must be both a good insulator and able to be polarized by an electric field.
Purified water on the other hand will be a better dielectric because it does not contain any significant amount of ions and is therefor not very conductive (i.e. is a better insulator than sea water).
I think (but don't quote me on an exam) that the reason alcohol is a poor dielectric is because it is not nearly as polar as water is, and according to the above, the second requirement for a dielectric is that it could be polarized by an electric field.
(This might also have to do with the size of the molecules, since water molecules are generally smaller than many kinds of alcohols, and can therefore re-orient themselves more easily in the presence of an electric field, but this is a guess.)
The Solvent Classifications section of this Wikipedia page also mentions that the polarity of a solution can be roughly gauged by the solution's dielectric constant. So this too seems to support the idea that polarity and dielectric properties are related.
If anyone has any improvements or corrections, please let me know in the comments and I'll update the answer accordingly.
Solution 2:
The dielectric's is effectively a measure of the solvents ability to hold a charge and the Ɛr is a measure of its permittivity.
From a chemical perspective the degree of this is inversely proportional to the born energy of an ion (or self ionization energy) so a solvent that is better at holding an electric charge like water will lower the energy requirements for a species to become an ion. Look up the Born equation, there are a few key relations in there but the main one would be the E=1/Ɛr relation, bigger dielectric, lower energy requirements.
Polarity and dielectric's are not the same thing, polarity relates to separation of charges over space, dielectric's relate to permeability and strengths of electric fields, but yes they do share some strong similarities and trends and a lot of the time you can make assumptions like "this solvent has a higher dielectric constant, so therefore will be more conductive. When talking about salts, 'dissolution' and 'solvation' are two different processes, dissolution happens first when the solvents electric field goes into the crystal lattice and lowers the energy requires for ionization, then the ions are solvated by solvents. First step is all about the dielectrics and is about ionizing the species in the lattice, the second step is all about the polarity and becomes some annoying surface physics issues where even geometries can muddle things.
But I feel like the main issue with computers in water is that there are dissolved minerals in water that will cause all sorts of redoxs to happen.