[Rowman Gentles]

Rowman Gentles asked the Naked Scientists:
   
What is the refractive index of water and vinegar?

What is the main factor that determine the refractive index of a liquid?

What do you think?

[lightarrow]

It depends on what you mean with "the main factor". Macroscopic or microscopic? Refractive index depends on the electric permittivity and magnetic permeability of the fluid, which in turn depends also on the molecular polarizability. Water molecules have an high dipole moment so, with a big extrapolation, we can say it has an high refractive index.


water:
http://hypertextbook.com/facts/2005/AmyHo.shtml

vinegar:
http://hypertextbook.com/facts/2005/refraction.shtml

[Bored chemist]

"Water molecules have an high dipole moment so, with a big extrapolation, we can say it has an high refractive index."
But actually, it doesn't, unless you are talking about refraction of radio waves.


One factor that correlates well with a high refractive index is a high atomic number. A high atomic number means that the atom has lots of electrons, than means some of them must be a long way from the nucleus so they are less rigidly held in place by the positive charge there.
Because they are less well held down they can interact more with passing light.

[lightarrow]

"Water molecules have an high dipole moment so, with a big extrapolation, we can say it has an high refractive index."
But actually, it doesn't, unless you are talking about refraction of radio waves.

In my previous post I talked of "molecular polarizability" so the dipole moment is not only the permanent one but the instantaneous too. Yes, polarizability is correlated with electronic cloud's dimensions and so with atomic number.