Final answer:
Salts that are used to remove permanent hardness of water are called water softeners, which include ion exchange resins, lime softening compounds, and chelating agents. These methods replace calcium and magnesium ions with sodium or other ions that don't cause hardness, thus softening the water.
Step-by-step explanation:
Salts used to remove permanent hardness of water are generally known as water softeners. These softeners work by replacing hard water minerals like calcium (Ca2+) and magnesium (Mg2+) with sodium (Na+) or other non-hardness causing ions. Methods such as ion exchange, lime softening, and the use of chelating agents like EDTA are common in the softening of water. In ion exchange, resins or zeolites capture the hard water ions and release sodium ions from their surface. Lime softening involves the addition of calcium hydroxide to induce the precipitation of calcium and magnesium.
Chelation utilizes compounds that form stable complexes with metal ions, preventing them from causing hardness. Commercial water softeners often use complex sodium salts that function as ion exchange resins for this purpose and provide treated water with fewer dissolved minerals but a slightly saltier taste due to the presence of sodium ions. Builders or chelating agents also soften water through processes like precipitation and chelation, particularly in regions with hard water.