Tricine (N-[Tris(hydroxymethyl)methyl]glycine) is commonly used as a buffer. Bas
ID: 1023397 • Letter: T
Question
Tricine (N-[Tris(hydroxymethyl)methyl]glycine) is commonly used as a buffer. Based on its structure, over approximately what pH range would a 50 mM Tricine solution be expected to be an effective buffer? Explain. Draw a graph to illustrate your reasoning. Which solution will provide the most buffering against added KOH: 0.1 M acetic acid (pK_a = 4.8) at pH 5.5; 0.1 M acetic acid at pH 4.8; 0.1 M acetic acid at pH 4.0; or 0.1 M methylamine (pK_a = 10.7) at pH 4.5? Explain your reasoning in words and/or diagrams. How would your answer change if HCl were added instead of KOH?Explanation / Answer
Tricine is a zwitterionic amino acid that has a pKa1 value of 2.3 at 25 °C, while its pKa2 at 20 °C is 8.15.
SO the best buffering range will be
pH = pKa + log base/acid
pH = 8.15 + log base/acid
Log base/acid is 0.5 is the best buffer activity
pH = 8.15 + 0.5 =8.65
pH = 8.15 - 0.5 = 7.65
SO the best buffer range is 7.65 - 8.65 this is irrespective of the concentration
Since you are adding KOH which is a base the best buffer will be the one which is acidic. Buffer action means it will not let pH change by more than +/-1 unit in pH
pKa of acetic acid is 4.76
pH = pKa + log base/acid
5.5 = 4.76 + log base/acid
base/acid = 5.5
Since total base+ acid is 0.1
base is 0.085 and acid is 0.015
Since you are adding base new pH max should be 6.5
6.5 = 4.76 + log base/acid
base/acid = 55
base = 0.098 and acid is 0.002
SO amount of base that can be added is 0.013 M
4.0 = 4.76 + log base/acid
base/acid = 0.18
Since total base+ acid is 0.1
base is 0.015 and acid is 0.085
Since you are adding base new pH max should be 5.0
5.0 = 4.76 + log base/acid
base/acid = 1.74
base = 0.064 and acid is 0.036
SO amount of base that can be added is 0.049 M
For methyl amine
4.5 = 10.7 + log base/acid
base/acid = 6.31 x 10-7
Since total base+ acid is 0.1
base is 0.0000001 and acid is 0.0999999
Since you are adding base new pH max should be 5.5
5.5 = 10.7 + log base/acid
base/acid = 6.31 x 10-6
base = 0.000001 and acid is 0.099999
SO amount of base that can be added is very small
SO the best buffer is 0.1M acetic acid at pH 4.0