A chemist needs to prepare a buffer using the carbonate system (information in the table below) with a final pH of 6. Which components should they mix in water to product this buffer?

Question

H2CO3 HCO3- CO32-
pKa 6.35 10.33 N/A

Answer 1

You write out the ionization expression and see what you have.
H2CO3 ==> H^+ + HCO3^-
k1 = (H^+)(HCO3^-)/(H2CO3) = ?
Since you want pH of 6, use the closest pKa value which is 6.35. That dictates you use HCO3 and H2CO3.