Water quality chemistry – identify the incorrect statement about pH and hydrogen-ion concentration Which of the following statements is incorrect regarding the pH scale and hydrogen-ion concentration in water?

Introduction / Context:
pH is a master variable for water treatment, corrosion control, and disinfection. Correct interpretation of pH relative to acidity and alkalinity is fundamental to process decisions.

Given Data / Assumptions:

• pH is defined as pH = −log10[H+], which equals log10(1/[H+]).
• Neutral water at 25°C has pH ≈ 7.
• Acidic solutions have pH < 7; alkaline (basic) solutions have pH > 7.

Concept / Approach:
Because pH is the negative logarithm, an increase of pH by 1 indicates a tenfold decrease in hydrogen-ion concentration. Therefore, statements that connect low pH with alkalinity are incorrect.

Step-by-Step Solution:
Check (a): pH = log10(1/[H+]) → correct.Check (b): higher pH → lower [H+] → correct.Check (c): lower pH → higher [H+] → correct.Check (d): lower pH gives alkalinity → incorrect; lower pH is acidic.

Verification / Alternative check:
Example: pH 5 has [H+] 100 times higher than pH 7, confirming acidity increases as pH decreases.

Why Other Options Are Wrong:
Only (d) conflicts with the pH definition; the others are standard relationships.

Common Pitfalls:
Equating alkalinity (acid-neutralizing capacity) with pH directly; while correlated, alkalinity is a buffering capacity, not simply pH.

Final Answer:
Lower pH gives an alkaline solution