Question

why are polar molecules soluble in polar solvents but not in non polar solvents

Answer 1

a rule in chemistry is "like dissolve likes"

everything you need to know: http://www.kentchemistry.com/links/bonding/LikeDissolveslike.htm

Answer 2

Polar covalent bonds are formed when electrons spend more time near one atom than the other. Most of these bonds are commonly formed between elements far apart on the periodic table.

Polar solvents contain bonds between atoms with very different electronegativity such as hydrogen and oxygen.

Non polar covalent bonds form when electrons are shared equally between the atom and typically form between atoms of the same element.

Non polar solvents contain bonds between atoms with similar electronegativity such as carbon and hydrogen.

Therefore, polar molecules are soluble in polar solvents but not nonpolar solvents because the molecules in the polar solvents are different in electronegativity and therefore can only form covalent polar bonds, the molecules cannot form non polar covalent bonds because the molecules aren't similar.