[spoonthrower]

So I just got out of my analytical chemistry midterm, and there was only one question I was completely clueless on.  Let me know what you guys think, so I can sleep tonight: How many mL of .5 M NaOH must be added to 10 g of Tris-HCl to make a buffer solution with pH= 7.6 with a total volume of 250 mL.  Given: MW Tris-HCl = 157.6 g/mol.  I was NOT given any pkb, pka, ka, or kb for Tris-HCl.  If I were to be given it on the exam I would have gotten this problem correct because I could have used Henderson-Hasselbach to solve for the amount of moles Tris-HCl converted to Tris-NaCl and used that info to calculate the amount of moles of NaOH needed to react in a 1:1 ratio with the original amount of Tris-HCl. Let me know if this problem is possible without being given a pka or pkb for tris-hcl. thanks.

[AWK]

You need pKb of Tris base or pKa TrisH⁺ (8.06). Then do stoichiometry of reaction
TrisHCl + NaOH
to get mixture of Tris/TrisH⁺ with needed pH