A buffer prepared by dissolving oxalic acid dihydrate ( H2C2O4⋅2H2O ) and disodium oxalate ( Na2C2O4 ) in 1.00 L of water has a pH of 4.957 . How many grams of oxalic acid dihydrate ( MW=126.07 g/mol ) and disodium oxalate ( MW=133.99 g/mol ) were required to prepare this buffer if the total oxalate concentration is 0.199 M? Oxalic acid has pa values of 1.250 ( pa1 ) and 4.266 ( pa2 ).