Which statement about pH adjustment is correct?

Which statement about pH adjustment is correct?

• A. Lime lowers pH; soda ash raises pH
• B. Lime and soda ash both raise pH
• C. Lime raises pH; soda ash lowers pH
• D. Lime lowers pH; soda ash lowers pH

Answer: (C)

In pH adjustment, adding bases raises the water’s pH by reducing acidity. Lime is calcium hydroxide, which supplies hydroxide ions directly, pushing pH higher and increasing alkalinity. Soda ash, sodium carbonate, also raises pH because it forms carbonate species in solution that consume hydrogen ions and release hydroxide ions, further increasing pH and alkalinity. Therefore, both lime and soda ash raise pH. The statement that lime raises pH but soda ash lowers it is not correct, and the ideas that lime lowers pH or that both reagents lower pH are also false.

In pH adjustment, adding bases raises the water’s pH by reducing acidity. Lime is calcium hydroxide, which supplies hydroxide ions directly, pushing pH higher and increasing alkalinity. Soda ash, sodium carbonate, also raises pH because it forms carbonate species in solution that consume hydrogen ions and release hydroxide ions, further increasing pH and alkalinity. Therefore, both lime and soda ash raise pH. The statement that lime raises pH but soda ash lowers it is not correct, and the ideas that lime lowers pH or that both reagents lower pH are also false.