Question

Explain the application of reverse osmosis in desalination of water.

Answer 1

Hint: Desalination refers to the removal of salts and minerals from a target substance. Saltwater (especially sea water) is desalinated to produce water suitable for human consumption or irrigation. Desalination processes are usually driven by either thermal (in the case of distillation) or electrical (in the case of reverse osmosis) as the primary energy types.

Complete answer:
Principle of reverse osmosis: It is a water purification process that removes ions, unwanted molecules and larger particles from drinking water using a semi permeable membrane. As a result, the solute is kept on the membrane’s pressurized side and the pure solvent is allowed to pass to the other side.
Reverse osmosis occurs when pressure is applied to the solution on the side of the membrane that contains the lower solvent concentration. The pressure forces the solvent to flow from a region of low concentration to one of high concentration.
When a pressure higher than the osmotic pressure is applied on the solution side (sea water) the water molecules moves from solution side to the solvent side through semi permeable membrane (opposite to osmotic flow), that is, solvent moves from where it is present in lower concentration to the region where it is present in higher concentration. Bacteria, viruses and pyrogen materials are rejected by the intact membrane. In this respect RO water approaches distilled water in quality.
In this way, desalination of seawater occurs. The pure/fresh water obtained is collected for use.
Generally, the semipermeable membrane (SPM) consists of cellulose acetate. However, Cellulose acetate membranes have limited pH tolerance. They degrade at temperatures greater than 35oC. They are vulnerable to bacteria. They eventually hydrolyze.

ADDITIONAL INFORMATION: The drawback of water obtained by reverse osmosis process is that it can significantly reduce these good minerals which can help in overall health of the heart and muscles. Those who use reverse osmosis as their primary source of water may suffer from side effects such as tiredness, muscle cramps, general weakness and cardiovascular disorders in severe cases.

Note:
Osmotic pressure is a colligative property of solutions that is observed using a semipermeable membrane, a barrier with pores small enough to allow solvent molecules to pass through but not solute molecules or ions. The net flow of solvent through a semipermeable membrane is called osmosis. The direction of net solvent flow is always from the side with the lower concentration of solute to the side with the higher concentration of solute or we can say that direction of net solvent flow is always from the side with the higher concentration of solvent to the side with the lower concentration of solvent.