Open Question
Does the pH increase, decrease, or remain the same on the addition of each of the following? (a) NH4NO3 to an NH3 solution (b) Na2CO3 to an NaHCO3 solution (c) NaClO4 to an NaOH solution
Ch.17 - Applications of Aqueous Equilibria
Chapter 17, Problem 59
The pH of a solution of HN3 (Ka = 1.9 x10^-5) and NaN3 is 4.86. What is the molarity of NaN3 if the molarity of HN3 is 0.016 M?
Verified step by step guidance1
Step 1: Recognize that the solution is a buffer solution, consisting of a weak acid (HN3) and its conjugate base (NaN3). Use the Henderson-Hasselbalch equation to find the relationship between pH, pKa, and the concentrations of the acid and its conjugate base.
Step 2: Calculate the pKa of HN3 using the given Ka value. The formula is \( \text{pKa} = -\log(\text{Ka}) \). Substitute \( \text{Ka} = 1.9 \times 10^{-5} \) into the formula to find pKa.
Step 3: Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pKa} + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right) \), where \([\text{A}^-]\) is the concentration of the conjugate base (NaN3) and \([\text{HA}]\) is the concentration of the weak acid (HN3).
Step 4: Substitute the known values into the Henderson-Hasselbalch equation: \( \text{pH} = 4.86 \), \( \text{pKa} \) from Step 2, and \([\text{HA}] = 0.016 \text{ M}\). Solve for \([\text{A}^-]\), the concentration of NaN3.
Step 5: Rearrange the equation to solve for \([\text{A}^-]\): \( \log\left(\frac{[\text{A}^-]}{0.016}\right) = \text{pH} - \text{pKa} \). Use the antilog to find \([\text{A}^-]\), which is the molarity of NaN3.
Related Practice
Open Question
Calculate the pH of a solution that is 0.25 M in HF and 0.10 M in NaF.
Open Question
Calculate the pH of a solution prepared by dissolving 0.10 mol of solid NH4Cl in 0.500 L of 0.40 M NH3. Assume that there is no volume change.
Textbook Question
The pH of a solution of NH3 and NH4Br is 8.90. What is the molarity of NH4Br if the molarity of NH3 is 0.016 M?
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Open Question
Which of the following gives a buffer solution when equal volumes of the two solutions are mixed? (a) 0.10 M HF and 0.10 M NaF (b) 0.10 M HF and 0.10 M NaOH (c) 0.20 M HF and 0.10 M NaOH (d) 0.10 M HCl and 0.20 M NaF
Textbook Question
Which of the following gives a buffer solution when equal volumes of the two solutions are mixed?
(a) 0.10 M NH3 and 0.10 M HCl
(b) 0.20 M NH3 and 0.10 M HCl
(c) 0.10 M NH4Cl and 0.10 M NH3
(d) 0.20 M NH4Cl and 0.10 M NaOH
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