This lecture explores the concept of chemical potential in mixtures and its application to osmosis and osmotic pressure. The instructor explains the phenomenon of osmosis, the selective permeability of semi-permeable membranes, and derives the Van't Hoff law to quantitatively describe osmotic pressure. The lecture delves into the equilibrium between solute and solvent, the calculation of osmotic pressure, and the practical application of the Van't Hoff law in determining osmotic pressure in biological systems.