In water chemistry, what aspect of pH is of interest to chemists?

• A. What is in the water, such as inorganics, organics, and algae, because they can influence the pH
• B. Whether the water is scale-forming or corrosive
• C. What makes up the pH and how much buffering exists
• D. The contaminants and their influence on pH

Answer: (C)

The main thing chemists focus on with pH is what sets it and how stable it is. pH is a measure of hydrogen ion activity in solution, and that activity comes from the acids and bases present. But just knowing the components isn’t enough—how resistant the pH is to change matters too. That resistance is the buffering capacity, which comes from the system’s buffers (weak acids and bases and their conjugates) and the overall alkalinity of the water. So the best understood aspect is what makes up the pH (the hydrogen ion activity produced by the acids and bases in the water) and how much buffering exists to keep pH from shifting when acids or bases are added.