Define osmotic pressure.

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Components:**
- A solution is composed of two main components: solute and solvent.
- The solute is the substance that gets dissolved, while the solvent is the medium in which the solute dissolves.

2. **Semi-Permeable Membrane:**
- A semi-permeable membrane is a barrier that allows certain molecules (like solvent) to pass through while blocking others (like solute).
- When a solution is placed on one side of a semi-permeable membrane, the solvent molecules tend to move from the solution to the area with less solvent concentration (usually pure solvent).

3. **Osmotic Flow:**
- This movement of solvent molecules from the solution through the semi-permeable membrane is known as osmosis.
- Osmosis continues until equilibrium is reached, where the concentration of solvent is equal on both sides of the membrane.

4. **Preventing Osmosis:**
- To prevent the flow of solvent from the solution through the semi-permeable membrane, an external pressure must be applied to the solution.
- This external pressure counteracts the natural osmotic flow of the solvent.

5. **Definition of Osmotic Pressure:**
- Osmotic pressure is defined as the additional pressure that must be applied to a solution to prevent the flow of solvent molecules through a semi-permeable membrane.
- It is a colligative property, meaning it depends on the concentration of solute particles in the solution rather than the identity of the solute.

**Final Definition:**
Osmotic pressure is the pressure required to stop the flow of solvent molecules from a dilute solution through a semi-permeable membrane into a more concentrated solution.

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