pH of water is 7 at $25^{\circ} \mathrm{C}$. If water is heated to $80^{\circ} \mathrm{C}$., it's pH will :

pH of water is 7 at $25^{\circ} \mathrm{C}$. If water is heated to $80^{\circ} \mathrm{C}$., it's pH will :
  1. Decrease
  2. $\mathrm{H}^{+}$concentration increases, $\mathrm{OH}^{-}$concentration decreases
  3. Remains the same
  4. Increase

Solution

At $25^{\circ} \mathrm{C}$, pure water has $\mathrm{pH}=7$
As temperature increased, water molecules dissociate more into hydrogen ions ( $\mathrm{H}^{+}$) and hydroxide ions $\left(\mathrm{OH}^{-}\right)$.
This increased dissociation leads to slightly decrease in pH.
At $80^{\circ} \mathrm{C}, \mathrm{pH} \approx 6.93$

Asked in: JEE Main 2025 (23 Jan Shift 2)

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