# What does the solubility of KNO3 depend on?

This is to do with the fact that $K N {O}_{3}$ is an ionic compound.
Ionic compounds dissolve in water and covalent compounds do not. The best example of this is NaCl (Sodium Chloride: table salt) - this is an ionic salt and dissolves readily in water. A covalent compound such as sand (Silicon Dioxide: $S i {O}_{2}$) does not dissolve in water.
This happens because the dipole water molecules attract the positive and negative ions and split them apart - in covalent compounds such as $S i {O}_{2}$ there is no electrical charge on the atoms, so they are therefore harder to break down.
In the case of ionic breakdown, then, the positive side of the water molecules attracts the negative $N {O}_{3}^{-}$ part of the ion, while the negative ${K}^{+}$ ion is attracted to the negative side of the water dipole.