pH

To change to subject from cum and hygiene, here's some chemistry for you...

A solution of CH3CH2COOH (Ka = 1,3*10^-5) and a strong base.
Acid: 0.50L 0.1M
Base: 0.20L 0.1M

What's the pH?

Well the strong base will abstract protons from 0.20 L of the acid, leaving an HA:A- ratio of 3:2

Then, using the henderson-hasselbach arrangment of the Ka equation:

pH = pKa + log(A-/HA) = 4.9 - 0.2 = 4.7