Osmosis
Definition and meaning of Osmosis in chemistry.
Osmosis is the spontaneous movement of solvent molecules across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. This process continues until equilibrium is reached or osmotic pressure balances the concentration gradient.
In more detail
In osmosis, the semipermeable membrane allows solvent molecules (usually water) to pass through but blocks or restricts the passage of dissolved solute particles. The driving force is the difference in solute concentration across the membrane, not direct attraction of water to solutes, but rather the statistical tendency of molecules to distribute evenly. Osmosis is crucial in biological systems, where cells rely on osmotic balance to maintain proper hydration and function. The phenomenon is quantitatively described by van't Hoff's equation, which relates osmotic pressure to solute concentration.
Key facts
| Field | Physical Chemistry |
|---|---|
| Driving Force | Solute concentration gradient (water potential difference) |
| Osmotic Pressure Equation | Pi = iMRT (i = van't Hoff factor, M = molarity, R = gas constant, T = absolute temperature) |
| Biological Significance | Maintains cell hydration and homeostasis in organisms |
When a cell is placed in a hypertonic salt solution, water molecules from inside the cell move outward across the cell membrane to the region of higher salt concentration, causing the cell to shrink (crenation).
Frequently asked questions
Is osmosis the same as diffusion?
No. Diffusion is the movement of any particles from high to low concentration across any boundary. Osmosis specifically refers to the movement of solvent molecules across a semipermeable membrane in response to a solute concentration gradient.
What is osmotic pressure?
Osmotic pressure is the minimum pressure required to prevent the net flow of solvent into a solution across a semipermeable membrane. It depends on the number of dissolved particles (solute concentration), not their identity or nature.