Pka=pH when[HA]=[A- ]. What is [A-]/[HA] WHEN PH=PKA+1 AND WHEN pH=pka-1

2 answers

pH = pKa + log (A^-)/(HA)
When (A^-)/(HA) = 1, log 1 = 0 and pH = pKa.

When pH = pKa + 1, (A^-)/(HA) = 10 BECAUSE log 10 = 1.

I'll leave the pKa-1 for you to do.
When pH = pKa - 1, (A^-)/(HA) = 0.1 BECAUSE log 0.1 = -1.