What is pH and pOH at 25°C?

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Multiple Choice

What is pH and pOH at 25°C?

Explanation:
In water at 25°C, the two key concentrations, [H+] and [OH−], are tied together by the autoionization constant Kw, which equals 1.0 × 10−14. The pH and pOH are simply the negative logarithms of these concentrations: pH = −log[H+], pOH = −log[OH−]. Because [H+][OH−] = Kw, taking logs gives pH + pOH = −log([H+][OH−]) = −log(Kw) = 14. So, at 25°C the sum of pH and pOH is always 14, regardless of whether the solution is acidic or basic (as long as temperature remains 25°C). The product pH × pOH is not a fixed value; it depends on the individual pH and pOH, and Kw changes with temperature, so the sum would not be 14 outside of 25°C.

In water at 25°C, the two key concentrations, [H+] and [OH−], are tied together by the autoionization constant Kw, which equals 1.0 × 10−14. The pH and pOH are simply the negative logarithms of these concentrations: pH = −log[H+], pOH = −log[OH−]. Because [H+][OH−] = Kw, taking logs gives pH + pOH = −log([H+][OH−]) = −log(Kw) = 14.

So, at 25°C the sum of pH and pOH is always 14, regardless of whether the solution is acidic or basic (as long as temperature remains 25°C). The product pH × pOH is not a fixed value; it depends on the individual pH and pOH, and Kw changes with temperature, so the sum would not be 14 outside of 25°C.

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