Multiple Choice
Using the Henderson-Hasselbalch equation, what is the pH of a buffer solution containing 0.6 M HF and 0.2 M NaF? The acid dissociation constant, Ka, for HF is 6.8 × 10^{-4}.
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18. Aqueous Equilibrium
Henderson-Hasselbalch Equation
Multiple Choice
Calculate mass of NaN3 that needs be added to 1.8 L of 0.35 M HN3 in order to make a buffer with a pH of 6.5. Ka of hydrazoic acid is 1.9 × 10−5.
A
1.4 g NaN3
B
1.0 × 10−2 g NaN3
C
2.5 × 103 g NaN3
D
3.55 g NaN3
Verified step by step guidance1
Understand the problem: We need to calculate the mass of NaN3 required to create a buffer solution with a specific pH using a given concentration of HN3. The buffer solution is formed by a weak acid (HN3) and its conjugate base (NaN3).
Use the Henderson-Hasselbalch equation to relate the pH of the buffer solution to the concentrations of the acid and its conjugate base: , where is the negative logarithm of the acid dissociation constant (Ka).
Calculate using the given Ka value: .
Rearrange the Henderson-Hasselbalch equation to solve for the ratio of the concentrations of the conjugate base to the acid: .
Calculate the moles of NaN3 needed using the concentration of HN3 and the volume of the solution. Then, convert moles to mass using the molar mass of NaN3: .
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