Chemistry
Chemistry
10th Edition
ISBN: 9781305957404
Author: Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher: Cengage Learning
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### Calculating the pH of a Solution Containing Ammonia and Ammonium Chloride

**Problem Statement:**

A solution is prepared at \(25 \, ^\circ \mathrm{C}\) that is initially \(0.16\, M\) in ammonia \((\mathrm{NH}_3)\), a weak base with \(K_b = 1.8 \times 10^{-5}\), and \(0.011\, M\) in ammonium chloride \((\mathrm{NH}_4\mathrm{Cl})\). Calculate the pH of the solution. Round your answer to 2 decimal places. 

**Solution:**

To calculate the pH of the solution containing ammonia and ammonium chloride, follow these steps:

1. **Determine the concentration of \(\mathrm{OH}^-\)** using the given \(K_b\):
   - Ammonia (\(\mathrm{NH}_3\)) is a weak base, which partially dissociates in water:
   
     \[
     \mathrm{NH}_3 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{NH}_4^+ + \mathrm{OH}^-
     \]
   
   - Using the given \(K_b\) value:
   
     \[
     K_b = \frac{[\mathrm{NH}_4^+][\mathrm{OH}^-]}{[\mathrm{NH}_3]}
     \]
     
     Given \( [\mathrm{NH}_4^+] \) from \(\mathrm{NH}_4\mathrm{Cl} = 0.011\, M\) and initial \([\mathrm{NH}_3] = 0.16\, M\).

2. **Set up the equilibrium expression:**
   
   \[
   1.8 \times 10^{-5} = \frac{(0.011 + x)x}{0.16 - x}
   \]
   
   Because \(K_b\) is very small, \(x\), the amount dissociated, will be very small relative to the initial concentrations; thus, we can approximate \(0.011 + x \approx 0.011\) and \(0.16 - x \approx 0.16\).
   
3. **Simplify the equation:**
   
   \[
   1.8 \times 10^{-5}
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Transcribed Image Text:### Calculating the pH of a Solution Containing Ammonia and Ammonium Chloride **Problem Statement:** A solution is prepared at \(25 \, ^\circ \mathrm{C}\) that is initially \(0.16\, M\) in ammonia \((\mathrm{NH}_3)\), a weak base with \(K_b = 1.8 \times 10^{-5}\), and \(0.011\, M\) in ammonium chloride \((\mathrm{NH}_4\mathrm{Cl})\). Calculate the pH of the solution. Round your answer to 2 decimal places. **Solution:** To calculate the pH of the solution containing ammonia and ammonium chloride, follow these steps: 1. **Determine the concentration of \(\mathrm{OH}^-\)** using the given \(K_b\): - Ammonia (\(\mathrm{NH}_3\)) is a weak base, which partially dissociates in water: \[ \mathrm{NH}_3 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{NH}_4^+ + \mathrm{OH}^- \] - Using the given \(K_b\) value: \[ K_b = \frac{[\mathrm{NH}_4^+][\mathrm{OH}^-]}{[\mathrm{NH}_3]} \] Given \( [\mathrm{NH}_4^+] \) from \(\mathrm{NH}_4\mathrm{Cl} = 0.011\, M\) and initial \([\mathrm{NH}_3] = 0.16\, M\). 2. **Set up the equilibrium expression:** \[ 1.8 \times 10^{-5} = \frac{(0.011 + x)x}{0.16 - x} \] Because \(K_b\) is very small, \(x\), the amount dissociated, will be very small relative to the initial concentrations; thus, we can approximate \(0.011 + x \approx 0.011\) and \(0.16 - x \approx 0.16\). 3. **Simplify the equation:** \[ 1.8 \times 10^{-5}
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