Acetic acid has a Ka value of 1.8 x 10^-5. How many grams of NaC2H3O2 would have to be added to 100ml of .10M HC2H3O2 to prepare a buffer with a pH of 4.5?

Question

Acetic acid has a Ka value of 1.8 x 10^-5.  How many grams of NaC2H3O2 would have to be added to 100ml of .10M HC2H3O2 to prepare a buffer with a pH of 4.5?

jfraser · Answer

the pH of a buffer is usually calculated with Henderson-Hasselbach:$$pH = pKa + \log([B]/[A])$$ where [B] and [A] are the concentrations of the conjugate base and acid. For this problem, you need to solve for [B], then turn that concentration into moles of NaC2H3O2 using the volume of solution, then into grams using molar mass.