A certain indicator, HA, has a 𝐾a value of 4.0×10−8. The protonated form of the indicator is red and the ionized form is blue. What is the p𝐾a of the indicator?

Answer 1

The pKa is the negative log of the Ka. You are given the Ka = 4.0x10^-8. Wouldn't that mean that

pKa = -log Ka

pKa = -log 4.0x10^-8

pKa = 7.40