In what process is calcium carbonate formed?

• A. Reverse osmosis
• B. Lime softening
• C. Filtration
• D. Coagulation

Answer: (B)

Calcium carbonate is formed during the lime softening process, which is widely used to reduce hardness in water. In lime softening, calcium hydroxide (also known as lime) is added to the water, and it reacts with the bicarbonate and carbonate ions present. This reaction leads to the formation of calcium carbonate, which precipitates out of the solution, allowing for easier removal from the water.

The formation of calcium carbonate during lime softening not only reduces water hardness by removing dissolved calcium and magnesium ions but also helps in controlling alkalinity levels in the water. This process is particularly effective in treating water with a high concentration of hardness-causing minerals, thereby improving both the aesthetic qualities and the suitability of the water for various applications.

In contrast, reverse osmosis primarily focuses on removing dissolved solids and is not specifically designed to produce calcium carbonate. Filtration is a physical process used to remove solid particles from water rather than chemical compounds. Coagulation involves adding chemicals to promote the agglomeration of suspended particles but does not result in calcium carbonate formation.