Multiple Choice
At what pH will alanine exist predominantly in its zwitterionic form, where it is overall uncharged?
17. Acid and Base Equilibrium
pH of Weak Acids
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An unknown weak acid has an initial concentration of 0.55 M. What is the pH of the solution if the weak acid also has a pKa of 5.79?
A
0.60
B
6.05
C
3.02
D
5.75
Verified step by step guidance1
Start by understanding the relationship between pH, pKa, and the concentration of a weak acid. The pH of a weak acid solution can be calculated using the formula: \( \text{pH} = \frac{1}{2} (\text{pKa} - \log [\text{HA}]) \), where \([\text{HA}]\) is the initial concentration of the acid.
Identify the given values: the initial concentration of the weak acid \([\text{HA}]\) is 0.55 M, and the pKa of the acid is 5.79.
Substitute the given values into the formula: \( \text{pH} = \frac{1}{2} (5.79 - \log(0.55)) \).
Calculate \( \log(0.55) \) using a calculator or logarithm table. This will give you the logarithmic value needed for the formula.
Finally, compute the expression \( \frac{1}{2} (5.79 - \log(0.55)) \) to find the pH of the solution. This will give you the pH value, which is the measure of acidity of the solution.
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