[brycebb]

You have 0.954g of an unknown acid H2A, which reacts with NaOH according to the balanced equation: H2A+2NaOH--->Na2A +2H2O.  If 36.04ml of 0.509M NaOH is required to titrate the acid to the second equivalence point, what is the molar mass of the acid?


I know you set it up like this,
0.03604L(0.509mol/L NaOH)(1mol H2A/ 2mol NaOH)= 0.00917218mol H2A.  Now I know this is not the correct mol value unless this were a monoprotic acid, but since it is diprotic you must do something to this value.  I assumed you divide this value by 2, to get one mol, then take 0.954g/0.00458609mol to get 208.8 g/mol.  Now the answer in the book is 104g/mol which is half of this value, can someone help me and show what I did wrong?

[JustinCh3m]

for every "1mol H2A", there are how many moles of H+?

[brycebb]

for every "1mol H2A", there are how many moles of H+?

I figured it out now, thanks