What two minerals are exchanged for sodium in water softeners?

The correct answer is that calcium and magnesium are exchanged for sodium in water softeners. Water softeners operate on the principle of ion exchange, where ions in hard water, specifically calcium and magnesium, are removed and replaced with sodium ions. These minerals are responsible for water hardness, which can lead to scale buildup in pipes and appliances.

In the ion exchange process, hard water passes through a resin bed that is initially saturated with sodium ions. As the water flows through, calcium and magnesium ions in the water are attracted to the resin and exchanged for sodium ions, which are released into the water. This effectively reduces the hardness of the water, providing "softened" water that is less likely to cause scaling and is often more compatible with soap and detergent usage.

Understanding this ion exchange process is crucial for effective water treatment and ensuring that the softened water meets the desired quality standards. The role of sodium in this context is significant as it not only helps in softening the water but also keeps the ion exchange resin operational until it requires regeneration, at which point the resin is flushed with a concentrated sodium chloride solution to replenish the sodium ions.