Examples of solvents include water, acetone, turpentine and ethanol and examples of solutes include salt, sugar, iodine and copper sulfate. A solvent must have the same polarity as the solute. An important phrase in chemistry is "like dissolves like."
"Like dissolves like" refers to the fact that polar solutes will dissolve in polar solvents and non-polar solutes will only dissolve in non-polar solvents. Polar solutes cannot dissolve in non-polar solvents. Water is a polar solvent, salt and sugar are both polar solutes. To dissolve iodine, which is non-polar, a solvent such as ethyl acetate would be needed and it would not dissolve into water.
The polarity of each solvent or solute substance depends on the covalent bonds it has between atoms. When two non-metal atoms bond, two electrons are shared between each of them. In covalent bonds, the electrons shared by each of the atoms are attracted to the nucleus of both atoms. The two forms of covalent bonding are polar and non-polar. Non-polar bonds are formed with an equal sharing of electrons between atoms. Polar bonds are formed when the sharing of electrons are uneven. Ionic bonds happen when there is a complete transfer of electrons between atoms. These ionic solutes can dissolve in both polar solvents and ionic solvents.