Final answer:
Water softening is the removal of hardness-causing ions, predominantly calcium and magnesium, from water. This can be achieved through lime softening, which precipitates these ions out; ion exchange, replacing hardness ions with sodium ions; and reverse osmosis, which uses a semipermeable membrane to filter out the hardness ions.
Step-by-step explanation:
The process used to reduce the hardness of water is known as water softening. One common method employed for water softening is lime softening. In this technique, calcium hydroxide, Ca(OH)2, also called 'slaked lime', is added to hard water. Raising the pH, this induces calcium and magnesium in the water to precipitate out as CaCO3 and Mg(OH)2, which can then be filtered out due to their low solubility in water.
An alternative approach is ion exchange. Hard water is passed through a column filled with a zeolite or resin, which traps the hardness ions, Ca2+ and Mg2+, and releases sodium ions, Na+, into the water. Through this ion exchange, hard water is softened as calcium and magnesium ions are effectively replaced with sodium ions.
Another technology used is reverse osmosis, involving high pressure to push water through a semi-permeable membrane. This membrane filters out larger ions and molecules responsible for water hardness, resulting in softened water. However, reverse osmosis can produce a significant amount of wastewater. It's essential to note that while hard water contains minerals like calcium and magnesium, softening the water makes it more suitable for cleaning and can prolong the life of plumbing systems.