pH buffer - make a pH buffer (Oct/25/2006 )

can you mix1.0 M formic acid and sodium formate to produce a pH of 3.900 and a formate ion concentration of 0.200 M? explain...

i've personnaly never did that, but what is the pKa of that acid?
answer for lazy ones : 3,74
so basically prepare solutions of 0.2M of each one (acid and base)
and mix til the pH reach the desired value !

my question : is "please" missing in your vocabulary?

EDIT : in your case mix the 2 solutions and dilute the final one by 5

then you would have to dilute to 0.2 M (5x) since your stocks are 1.0 M.