What is the primary function of the semipermeable membrane in reverse osmosis?

The primary function of the semipermeable membrane in reverse osmosis is to allow the passage of water while restricting the movement of many dissolved substances, such as salts, impurities, and other contaminants. This selective permeability is crucial for the reverse osmosis process, which is designed to purify water by forcing it through the membrane under pressure.

The membrane's unique properties enable it to permit water molecules to pass through, while effectively blocking larger molecules and ions. This selective filtration helps achieve a high level of water purification, making it suitable for applications such as drinking water treatment and desalination. Thus, the ability of the semipermeable membrane to specifically allow the passage of water, while simultaneously rejecting other substances, underscores its essential role in the reverse osmosis process.