What is the pH of pure water at 40°C?

Question

At 40°C, the value of Kw is 2.92 10-14. Furthermore, If the hydroxide ion concentration in a solution is 0.44 M, what is the pH at 40°C?

Answer 1

The self dissociation of water is

H2O <=> H+ +OH-

with Kw=[H+][OH-].

Kw changes with temperature and therefore the pH of pure water is different at different temperatures.

For pure water, according to the reaction above, [H+]=[OH-] thus

Kw=[H+]^2 => [H+]=Kw^(1/2) =>
pH= -log[Kw^(1/2)]= -(1/2)*log(Kw)
so pH= -0.5*log(2.92*10^-14) = 6.77.

For the second part,

Kw=[H+][OH-] =>
-log(Kw)=pH + (-log[OH-]) =>
pH= log(0.44) -log(2.92*10^-14) =13.18

Answer 2

NONONO

The first answerer is correct, the pH of water does not change with temperature. However, the pH of water is 7 NOT 0!!!!!!

Answer 3

If the water is pure wouldn't the pH be 0?

Answer 4

For water, the pH is always 0.

Answer 5

pH shouldn't change no matter the temperature. I think. -_-;