The mole is formally introduced in this video lesson as a large number by which atoms and molecules are counted. The concentration of solutions is often given in units of moles per liter so that the chemist is able to get a handle on the number of atoms or molecules within the solution. Duration: 8:52.

Kai and Maile explore the terms used to describe solutions. Kai distinguishes between solute and solvent, while Maile looks at different ways that concentration are measured. Duration: 4:01.