How do you determine if a molecule is polar or non-polar

You would determine if a molecule is polar or non-polar by Mainlydissolving it in water - or any other polar solvent

Explanation:

Polar molecules will dissolve in water while non-polar will not.

This is because polar molecules have dipoles (partially positive and partially negative ends in the molecule). This means it can interact positively by forming hydrogen bonds with water (hydrophilic), or weak electrostatic forces with molecules of any other polar solvent, Non-polar molecules do not bear this property and are hydrophobic.