Which compound is commonly used to raise pH by increasing alkalinity in water treatment?

• A. Soda ash (sodium carbonate)
• B. Lime
• C. Sodium chloride
• D. Calcium sulfate

Answer: (A)

Raising pH by increasing alkalinity relies on adding a chemical that enhances the water’s buffering capacity against acids. Soda ash, or sodium carbonate, dissolves to carbonate ions, which increase both alkalinity and the ability of the water to resist pH changes. This buffering helps push pH upward while preventing large swings when acids are introduced downstream in treatment processes. It’s commonly used because it effectively raises pH and buffering capacity with relatively minimal effect on calcium hardness, unlike lime, which adds calcium as well as raising pH and alkalinity. The other options don’t provide this buffering effect: sodium chloride doesn’t raise alkalinity, and calcium sulfate mainly affects hardness and sulfate levels rather than buffering pH.