The process of flow of a solvent from a lower concentration to a higher concentration of solution through a semipermeable membrane is a colligative property and is known as osmosis. Osmosis has a large importance in our daily life as well as industrial applications.
1. Raw mangoes can be pickled when placed in concentrated salt-water which is a hypertonic solution and causes the mangoes to shrivel.
2. Many areas in animal and human bodies are known to transport water in and out of cells is through osmosis and diffusion.
3. Wilted flowers when placed in pure water revive to become fresh again. Even carrots which shrink and wilt due to loss of water to the atmosphere can be placed in fresh water to regain the shape.
4. Water flows through the plant roots and towards all the parts of the plant partially through osmosis.
5. Preservation of meats and fruit is carried out by salting, pickling and adding high amounts of sugar. The hypertonic salt outside the fruits and meats causes the water to flow out of the cell and reduce bacterial growth and increase shelf life of the products. Also, the hypertonic solution causes bacterial cells to lose their water content, causing them to shrivel and die.
6. Industrial applications of osmosis are numerous. Processes include power generation, desalination, wastewater treatment, food processing, medical product enrichment, drug release and others.
7. One of the most important applications of osmosis is reverse osmosis. In the case of osmosis, the lower concentrated solution or pure solvent flows through a semipermeable membrane to the higher concentrated solution. Osmotic pressure is the pressure required to stop this flow of solvent molecules through the semipermeable membrane. When enough pressure is applied on the hypertonic solution compartment, the process is reversed and pure solvent molecules flow from the hypertonic side to the hypotonic side through the semipermeable membrane.
8. Reverse osmosis is used for desalination of seawater and technology of the same exists in water purifiers.
Figure 2: A simplistic image of reverse osmosis. A: Piston and input B: Hypertonic solution C: Solute molecules D: Semipermeable membrane E: Pure solvent F: Output. Image obtained under Creative Commons license. By Colby Fisher - Own work, CC BY-SA 3.0.
9. In this process, when pressure higher than the osmotic pressure of the saline solution is applied, pure water is pushed through the SPM into the pure water (solvent) side. The pressure applied is very high for this to be successful.
10. The SPM used is cellulose acetate film which allows molecules of water to pass through but not impurities or ions.
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