Let's look at an example where we find Kw, when we are not at 25 degrees Celsius. The pH of a pure water sample at 80 degree Celsius is 6.182. What is Kw at this temperature? The first thing we need to remember is that water undergoes auto-ionization, and so we end up with H2O in equilibrium with H+(aq), and OH-(aq). Now, we're given the pH of the solution as 6.182, which means we can use this to find the H+ concentration. So, pH equals negative log of H+, and if we rearrange that we can find that the H+ concentration equals 10 to the minus pH. So now I can substitute the pH that I'm given H+ =10 to the -6.182, and when I solve for that, I end up with [H+] = 6.57 x 10 to the minus seventh molar. This is a reasonable amount it's somewhere close to what we see at 25 degrees Celsius but not exactly. And then also we have to realize that for every age plaster that's produced in this auto ionization, I'll also produced one So what I also know is that the H+ concentration is equal to the Concentration. Now, when I want to find the value of Kw, I know that Kw equals the concentration of H+ times the concentration of And I can substitute in the concentration I found 6.57x10 to the -7th and I'm going to square that because I have H+ times the same value. And what I find is that Kw = 4.33 x 10 to the -13.