What chemical compound is primarily used for softening water?

The primary chemical compound used for softening water is lime, often in combination with soda ash. The process of softening water involves the removal of hardness-causing minerals, primarily calcium and magnesium ions. Lime (calcium hydroxide) is introduced to the water to precipitate these ions as insoluble compounds, effectively reducing water hardness.

When lime is added, it reacts with the calcium and magnesium to form precipitates that can then be filtered out. Soda ash (sodium carbonate) is often used alongside lime to enhance the precipitation process and regulates pH levels. Together, these compounds work efficiently to soften water, making them vital in water treatment processes.

In contrast, sodium chloride is primarily used for water softening through ion exchange processes, while calcium sulfate does not contribute to softening and can even add to hardness. Potassium permanganate is mainly used as an oxidizing agent in water treatment and does not play a role in softening water. Therefore, lime combined with soda ash is the most accurate choice for the water softening process.