pH - Weak Acids

Question 1

State the two approximations assumed for calculating the pH of weak acids.

Answer 1

1. [ H+ ] = [ A- ]
   So, [H+]^2
2. [ HA ] eqm = [ HA ] start

Question 2

What is the simplified Ka expression for weak acids?

Answer 2

Ka = [ H+ ] ^2 / [ HA ]

Question 3

In which situations are the approximations not justified?

Answer 3

1. Very weak acids or very dilute solutions
2. Stronger weak acids