how do i answer this question?

Question

What is the ratio of ionized/deionized cacodylate at pH 5 (pKa = 6.2)?

Answer 1

Use the Henderson-Hasselbalch equation:

pH = pKa + log A/HA

where A = ionized form and HA = acid form (unionized)

The problem wants ratio of ionized (A) to unionized or acid form (HA), which is A/HA:

5 = 6.2 + log A/HA

5-6.2 = log A/HA

-1.2 = log A/HA

A/HA = antilog (or inverse log) -1.2 = 0.06

A/HA ratio is 0.06