Which chemical is commonly used to soften water through chemical precipitation?

Lime, or calcium hydroxide, is commonly used in water treatment processes to soften water through chemical precipitation. The softening process typically involves the removal of calcium and magnesium, which are responsible for water hardness. When lime is added to water, it reacts with these hard ions to form insoluble precipitates, specifically calcium carbonate and magnesium hydroxide, which can then be removed through sedimentation or filtration. This process not only reduces hardness but also improves water quality, making it more suitable for various uses like in drinking water systems and industrial applications.

Other options like sodium chloride and potassium bicarbonate do not soften water through precipitation; instead, they may influence other aspects of water chemistry. Magnesium sulfate, while a soluble salt, does not effectively remove hardness ions, which is the primary goal of water softening. Thus, lime’s ability to precipitate hardness-causing ions makes it the preferred choice for this process.