Pure water has a pH of 7 at which of the following temperatures?

Question

Pure water has a pH of 7 at which of the following temperatures?

1. A. 100°C
2. B. 51°C
3. C. 32°C
4. D. 25°C (Correct answer)

Correct Answer

Option D — 25°C

Detailed Solution & Explanation

The correct answer is 25°C.

Key Points

• Pure water has a pH of exactly 7 at 25°C (298 K) — this is the standard reference temperature at which [H⁺] = [OH⁻] = 10⁻⁷ mol/L. At higher temperatures, water dissociates more, lowering the pH below 7 even though it remains neutral (e.g., pH ≈ 6.14 at 100°C).