Science & Nature · 2
What is the pH of pure water at 25°C?
Answer
7
Pure water at 25°C (77°F) has a pH of exactly 7.0, which is defined as neutral on the pH scale. The pH scale, ranging from 0 to 14, measures hydrogen ion (H+) concentration using the formula pH = -log[H+]. Pure water undergoes autoionization, producing equal concentrations of H+ and OH- ions (10^-7 molar each) at 25°C. The neutral point shifts with temperature: at higher temperatures, pure water has a pH below 7 because autoionization increases. The pH scale was developed by Danish biochemist Søren Peder Lauritz Sørensen in 1909.
💡 Did you know?
The pH scale (0-14) has 7 as neutral; below 7 is acidic (lemon juice ~2), above 7 is basic (bleach ~13).
Other options people guess
- 5
- 6
- 8
Topics
- chemistry
- acids-bases
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