Saturday, February 9, 2019

homework - Amphoteric amino acid titration


Glycine (NHX2CHX2COOH) is an amino acid with two pKa values (pKa,1=2.0, COOH; pKa,2=10.0, NHX2).




  • (a) If 0.01 mol of this amino acid is used to prepare one 1 L solution. Calculate the pH and the NHX3X+CHX2COOH concentration in the solution.




  • (b) If 10 mL of the above glycine amino acid solution is mixed with 90 mL of basic buffer system. If the concentration of the NHX2CHX2COOX was identified to be 1.05104M indicate the pH of the glycine solution.





  • (c) If 10 mL of strong base NaOH (0.01 M) was added to solution in (a) what is the final \mathrm{p}\ce{H}.







For part (a)
I used [H+]=10100.01=106.
Then I used pH=14log(106) to get a pH of 8.
While my NHX3X+CHX2COOH is 106 L.







For part (b)
I used the Henderson-Hasselbalch equation for a basic buffer pH=pKa+log([NHX2CHX2COOX ][NHX2CHX2COOH]) I got a pH of 10.97. But I'm unsure of my answer.






For part (c) I suspect that it is a basic buffer but I'm not sure which value to use. could anyone help me out with this.





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