Which treatment chemical raises pH?

Which treatment chemical raises pH?

• A. chlorine
• B. sodium hypochlorite
• C. alum
• D. ferric sulfate

Answer: (B)

pH shifts are driven by whether a chemical is acidic or basic in water. Alum and ferric sulfate are acidic coagulants; when they dissolve and hydrolyze, they release hydrogen ions, which lowers the pH. Chlorine added as chlorine gas or as hypochlorous acid can form acidic species, also tending to lower pH. Sodium hypochlorite, however, is a basic compound; its solution contains hydroxide ions, so adding it raises the pH. That makes sodium hypochlorite the chemical that increases pH. In practice, pH changes from disinfection and coagulation are monitored and adjusted as needed to keep treatment within the desired range.

pH shifts are driven by whether a chemical is acidic or basic in water. Alum and ferric sulfate are acidic coagulants; when they dissolve and hydrolyze, they release hydrogen ions, which lowers the pH. Chlorine added as chlorine gas or as hypochlorous acid can form acidic species, also tending to lower pH. Sodium hypochlorite, however, is a basic compound; its solution contains hydroxide ions, so adding it raises the pH. That makes sodium hypochlorite the chemical that increases pH. In practice, pH changes from disinfection and coagulation are monitored and adjusted as needed to keep treatment within the desired range.