A280.0 ml buffer solution initially contains 2.0×10−2 m of hcho2 and 2.0×10−2 m of nacho2. for formic acid, ka=1.8×10−4. in order to adjust the buffer ph to 4.20, should you add naoh or hcl to the buffer mixture?

In order for one to adjust the pH of a buffer mixture to a pH of 4.20, one should add HCl to the mixture. This is because the preferred pH is at the acidic range and you should be adding an acid to reach this pH. When adding a base, the pH will be farther from the desired one.

Wish i can but don’t know this

This would be canberra.