Why can't some substances dissolve in water? Chemically?

Question

anonymous · Answer

Water is a polar molecule. If a solute dissolved in water is polar molecule, it will dissolve in water. If a solute dissolved in water is non-polar like oil it will not dissolve in water.

b/c polar dissolves in polar

blues · Answer

Shruti is correct: water is a polar molecule. Polar means that the molecule has a partially negatively charged end and a partially positively charged end. These partial charges will be attracted to partial charges in other polar substances - like, for example, the substance that it is trying to dissolve. This leads to water dissolving the polar substance because it disrupts the other non-covalent bonds which hold the molecules in the polar substance together.

Substances without polar molecules don't have this problem - they don't have partial charges so water is not able to disrupt the non-covalent bonds holding them together. So water can't dissolve them.

For what can and cannot be dissolved, there is a saying in chemistry: "Like dissolves like." If you have a substance made out of polar molecules, a polar solvent like water can dissolve it. If it is made out of non-polar molecules, then a non-polar solvent can dissolve it. Hope that is helpful.

anonymous · Answer

yah @blues it should be like dissolves like.i wrote it in a wrong way