An ion-exchange softener utilizes resin beds to exchange which ion to soften water?

An ion-exchange softener utilizes resin beds primarily to exchange calcium and magnesium ions for sodium ions, which effectively softens the water. The process of water softening works by removing the bivalent ions (calcium and magnesium) that contribute to water hardness and replacing them with univalent sodium ions.

When water passes through the resin bed, the hard water ions attach to the resin, and sodium ions are released into the water in equal amounts. This exchange not only reduces the hardness of the water but also prevents the formation of scale buildup in plumbing and appliances, which can be caused by the presence of calcium and magnesium ions.

The choice of sodium as the ion used in the softening process is particularly important because it helps maintain the water's overall balance and keeps it less corrosive than other ions such as calcium or magnesium.