[sarah9625]

I have to tritrate a weak acid with NaOH 0.10mol/L to determine an unknown sample. I have a list of the acids and pKa values. One of the unknowns could be formic acid, MW=46.03g/mol, pKa=3.75. My titration volume needs to be between 10ml and 50ml. WHAT ARE THE SMALLEST AND LARGEST MASSES OF FORMIC ACID THAT WOULD GIVE TITRATION VOLUMES IN THESE LIMITS?

I think I can use the equation: pH=pKa+log(vloume of the base/volume of the base at equillibrium-volume of the base). Where to go from here I have no clue.
Any advice would be wonderful:)

[Borek]

pKa is of no use here, it only changes pH at the titration endpoint. What you are asking for is simple stoichiometry - start with reaction equation. Table you have can be handy as you will need molar masses of the acids in your calculations.

[sarah9625]

how about:

0.10/L  x  1L/1000  x  10ml/1  x  46.03g/1mol  =  0.05g   (is the smallest mass)

and

0.10/L  x  1L/1000  x  50ml/1  x  46.03g/1mol  =  0.23g   (is the largest mass)

Is that right?

[Borek]

Is that right?

Yep

The most important thing is that you may titrate between 0.001 and 0.005 mole of monoprotic acid (around 0.004 mole being the best amount). You may convert moles to mass any time you need.