At 373 K (100°C), the ionic product of water (Kw) increases to approximately 1.0 * 10^-12. What is the pH of pure, neutral water at this elevated temperature?
Answer and explanation
Correct answer: B. 6.0
.
- Step 1: The auto-ionization of water is an endothermic process: , .
- Step 2: As temperature rises from 298 K to 373 K, the equilibrium shifts forward, increasing from to .
- Step 3: In pure water, neutrality requires by definition.
- Step 4: Since :
- Step 5: The pH of neutral water at 373 K is: .
Answer
6.0
Why not the others: '7.0' is the neutral pH exclusively at 298 K (25°C); '8.0' would represent a basic solution where ; '12.0' is the value of , not .
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