What is the pH of pure water at 25 C (298K)

The pH of a solution is a measure of the concentration of hydrogen ions it contains. The pH of pure water at 25 degrees Celsius (298K) is 7. This is because water auto-ionizes (or self-ionizes) to form equal concentrations of H+ (hydrogen) ions and OH- (hydroxide) ions.

Here's the step-by-step explanation:

1. Water auto-ionizes into H+ and OH- ions according to the equation: 2H2O(l) ⇌ H3O+(aq) + OH−(aq)

2. At 25 degrees Celsius, the concentrations of these ions in pure water are both 1.0 x 10^-7 M (Molar).

3. The pH is calculated as the negative logarithm (base 10) of the H+ ion concentration. So, pH = -log[H+]

4. Substituting the value of [H+] into the equation gives: pH = -log(1.0 x 10^-7) = 7

So, the pH of pure water at 25 degrees Celsius is 7, which is considered neutral on the pH scale.