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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: nimerra12 on October 31, 2007, 03:06:02 PM

Title: Homework Help
Post by: nimerra12 on October 31, 2007, 03:06:02 PM

Hi everyone,

 I've hit a road block with this problem:
   For a triprotic acid H3A, Ka1 = 6.0*10^-3, Ka2 = 1.0 * 10^-7, and Ka3 = 3.0 * 10^-12. Describe how you would make a buffer with pH = 7 starting with 20.8 g of Na3A (molar mass 208 g/mol) and 0.100 M HCl or 0.100 M NaOH.

 I have the equations I need for each Ka and I have the chemical equations I need...I also know I need the Henderson-Hasslebach (sp?) equation to solve, I just don't know where to go from here. Any advice?

Title: Re: Homework Help
Post by: Borek on October 31, 2007, 05:15:21 PM

Henderson-Hasselbalch (http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch) it is.

Think about stoichiometry of what is happening when you add strong acid tou your Na₃A.