How many grams of sodium benzoate(MM=144) should be added to 200. ml of 1.0 M benzoate acid(HC7H5O2, Ka=6.5x10^-5) to prepare a buffer with a pH of 4.00

Question

anonymous · Answer

the answer is 19g

anonymous · Answer

Hasselbach equation isnt allowed to solve for this btw.

jfraser · Answer

then use a RICE box (or ICE table, whichever you prefer to call it)

anonymous · Answer

how, i only know how to do it to find ml

jfraser · Answer

knowing the desired pH lets you find the necessary H+ concentration. Knowing the pKA lets you find the H+ concentration that the acid would have by itself. Use stoichiometry to find the moles of sodium benzoate needed to shift the equilibrium to make the necessary changes to the H+ concentration. Turn those moles into grams.

anonymous · Answer

I got 93.6g.. I can't figure out what I did wrong.

anonymous · Answer

6.5x10^-5 = (1x10^-4)[C7H5O2-]/[HC7H5O2]

anonymous · Answer

0.65= [C7H5O2-]/[HC7H5O2]

anonymous · Answer

0.65 = (xM C7H5O2-)/(1.0M HC7H5O2)

anonymous · Answer

xmol = 0.65mol C7H5O2- , 0.65mol C7H5O2(144g/mol) = 94g