Osmosis is the process in which solvent molecules moves through a semipermeable membrane from a region of higher concentration to a region of lower concentration until the amount of fluid is equalised on both sides of the semipermeable membrane. The fluid that passes through the semipermeable membrane is known as the solvent, while the dissolved substance in the fluid is known as the solute. A solution that is separated from another solution by a semipermeable membrane can have three osmotic states: isotonic, hypotonic and hypertonic. In an isotonic solution is the pressure at both sides of the membrane the same. A hypotonic solution has a lesser number of solute particles than the solution to which it is compared. A hypertonic solution has a higher number of solute particles. At equilibrium is a solution always isotonic.
This video explains how to study osmosis using a potato osmometer.