[crusher]

I really need any and all advice out there, I am just stuck   


What volume of 0.25M NaOH and weight of citric acid (MW 192) must be used to prepare 1.0 L of 0.3 osmolar sodium citrate, pH 6.0?  pK1 = 3.1; pk2 = 4.74; pK3 = 5.4.

[Borek]

Use pKa3 and Henderson-Haselbalch equation to find out molar ratio of citric acid and base, then write equation for total osmolality of the solution. You will get two equations in two unknowns.

[crusher]

Borek
  Thanks for the *delete me*
Since we have 0.3 osmolar sodium citrate this is equilavent to 0.6 mol/L, correct?

Is the conjugate base or salt molarity used in the HH equation for this problem?

so, 6.0 = 5.4 + log 0.3 mol/x       OR       6.0 = 5.4 + log 0.6/x

Do we want total osmolality or total osmolarity??  Not that it will make much difference for an aqeous soln.

[Borek]

Beware: it is a mixture of Na2HCitrate and Na3Citrate, when calculating osmolarity concentration of first has to be mutiplied by 3, of the second - by 4.

HH must contain concentrations of Citrate-3 and HCitrate-2.