What is pH of pure water at 70o C

7.0

No, the pH isn't 7.0 because Kw is not 1E-14. I looked on the web and didn't find Kw but you need to look up Kw at 70 C. I found it at 10, 20. 30,. 40, 50 and 100 C but not 70 C.

Then (H^+) = sqrt Kw
and pH = -log(H^+).
Kw at 50 is about 5.5E-14 and at 100 it is abou5 50E-14 so I can't even guess at the Kw at 70 C.

slightly less than 7

To find the pH of pure water at a specific temperature, you need to know the value of the autoionization constant at that temperature.

At 25°C, the autoionization constant of water (Kw) is defined as Kw = [H+][OH-] = 1.0 x 10^-14.

However, at 70°C, the autoionization constant changes. Using the equation to calculate Kw: Kw = [H+][OH-], we can find the new value for Kw at 70°C.

To calculate the new value, you would need to find the concentration of H+ ions ([H+]) at 70°C. Since pure water is neutral, the concentration of H+ ions equals the concentration of OH- ions. Therefore, [H+] = [OH-].

Let's assume that the concentration of H+ ions at 70°C is x. Therefore, [H+] = [OH-] = x.

Using the equation for Kw, we have:

Kw = [H+][OH-] = x * x = x^2

We know that Kw = 1.0 x 10^-14 at 25°C, so let's solve for x at 70°C:

x^2 = 1.0 x 10^-14

Take the square root of both sides:

x = √(1.0 x 10^-14)

Using a calculator, you would find that x ≈ 3.16 x 10^-8.

Since [H+] = [OH-] = x, the concentration of H+ ions in pure water at 70°C is approximately 3.16 x 10^-8 M.

To find the pH, which is the negative logarithm of the H+ concentration, you would use the formula:

pH = -log[H+]

Substituting the value of [H+], we have:

pH = -log(3.16 x 10^-8)

Using a calculator, you would find that the pH of pure water at 70°C is approximately 7.5.