Why is oil unable to dissolve well in water? Water is polar and oil is nonpolar, which means they have no attraction for each other. Oil molecules are too large to fit between the closely spaced water molecules in the liquid state. Water has a greater density than oil, which means that they are not compatible for mixing together. The cohesive properties of water molecules make it difficult for substances like oil to dissolve.

Because water is polar and oil is nonpolar, their molecules are not attracted to each other. The molecules of a polar solvent like water are attracted to other polar molecules, such as those of sugar. This explains why sugar has such a high solubility in water. Ionic compounds, such as sodium chloride, are also highly soluble in water. Because water molecules are polar, they interact with the sodium and chloride ions. In general, polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. This concept is often expressed as "Like dissolves like." So many substances dissolve in water that it is sometimes called the universal solvent. Water is considered to be essential for life because it can carry just about anything the body needs to take in or needs to get rid of.