Question

What is the [ch3co2-]/[ch3co2h] ratio necessary to make a buffer solution with a ph of 4.34? ka = 1.8 × 10-5 for ch3co2h?

Answer 1

According to Henderson–Hasselbalch Equation,

                                    pH  =  pKa + log [Acetate] / [Acetic Acid]

As,
           pKa = -log Ka
           pKa = -log (1.8 × 10⁻⁵)
           pKa =  4.74
So,
                               pH  =  4.74 + log [Acetate] / [Acetic Acid]

                                  4.34  =  4.74 + log [Acetate] / [Acetic Acid]

                        4.34 - 4.74  = log [Acetate] / [Acetic Acid]

                                 -0.40  =  log [Acetate] / [Acetic Acid]

Taking Antilog on both sides,

               [Acetate] / [Acetic Acid]  =  0.398