1. A buffer with a pH of 4.51 is made from acetic acid/acetate ion conjugate pai
ID: 522865 • Letter: 1
Question
1. A buffer with a pH of 4.51 is made from acetic acid/acetate ion conjugate pair. Which of these solutions will give the correct buffer pH AND have the greatest buffer capacity? The pKa for acetic acid is 4.75.
a. [NH4+] = 0.2381, [NH3] = 0.1552
b. [NH4+] = 0.3174 , [NH3] = 0.1827
c. [NH4+] = 1.5 , [NH3] = 1.4772
d. [NH4+] = 0.04174 , [NH3] = 0.02402
e. none of these
*Note that all of these values are in molarity. The answer D is wrong.
2. Each of the following monoprotic acids were titrated with potassium hydroxide. If we start off with 0.02 F solutions of each one, which acid will give the most poorly defined inflection point in the titration curve?
a. pKa = 5.61
b. pKa = 7.88
c. pKa = 1.83
d. pKa - 7.00
e. none of these.
Explanation / Answer
Ans 1. b. [NH4+] = 0.3174 , [NH3] = 0.1827
Using henderson hasselbalch equation
pH = pKa + log [base] /[ conjugate acid]
4.51 = 4.75 + log 0.1827 / 0.3174
4.51 = 4.75 - 0.24
4.51 = 4.51
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