Question 1

What is the pH of pure water?

Accepted Answer

Pure water has a pH of 7.0 at 25°C, which is neutral. However, pH of pure water varies with temperature: it is about 7.47 at 0°C and 6.14 at 100°C, because the water autoionization constant (Kw) changes with temperature.

Question 2

How do buffer solutions work?

Accepted Answer

Buffer solutions contain a weak acid and its conjugate base (or vice versa). When acid is added, the conjugate base neutralizes it. When base is added, the weak acid neutralizes it. This keeps pH relatively stable within about 1 unit of the pKa value.