Quiz #4
Buffers and Titrations
Chemistry 121
March 7, 2005
Name:______________________
SN: ______________________
1. Histidine, one of the essential amino acids, was titrated with sodium hydroxide
producing the titration curve below.
a. Is histidine monoprotic, diprotic, or triprotic?
TRIPROTIC
b. Determine each pKa for histidine.
2.0, 6.0, and 9.0 (all ish)
c. What are good buffering ranges for histidine?
1-3
5-7
8-10 (all ish)
2. Calculate the pH of a solution containing 0.050 M CH3CO2H (acetic acid, Ka =
1.8 x 10-5) and 0.150 M CH3CO2Na (sodium acetate)
From pH = pKa + log (base/acid) you get 5.22
3. What would the pH be when 0.050 moles of gaseous HCl is added to 1 L of the
above solution?
In that case you would have converted 0.050 mol of the acetate to acetic acid
using the HCl, making the concentration of the acid equal to the concentration of
the base, so the pH = the pKa