Table of contents

1. Intro to General Chemistry3h 48m
2. Atoms & Elements4h 16m
3. Chemical Reactions4h 10m
4. BONUS: Lab Techniques and Procedures1h 38m
5. BONUS: Mathematical Operations and Functions48m
6. Chemical Quantities & Aqueous Reactions3h 53m
7. Gases3h 49m
8. Thermochemistry2h 37m
9. Quantum Mechanics2h 58m
10. Periodic Properties of the Elements3h 9m
11. Bonding & Molecular Structure3h 29m
12. Molecular Shapes & Valence Bond Theory1h 57m
13. Liquids, Solids & Intermolecular Forces2h 23m
14. Solutions3h 1m
15. Chemical Kinetics2h 53m
16. Chemical Equilibrium2h 29m
17. Acid and Base Equilibrium5h 1m
18. Aqueous Equilibrium4h 47m
19. Chemical Thermodynamics1h 50m
20. Electrochemistry2h 42m
21. Nuclear Chemistry2h 36m
22. Organic Chemistry5h 7m
23. Chemistry of the Nonmetals2h 39m
24. Transition Metals and Coordination Compounds3h 16m

17. Acid and Base Equilibrium

pH of Weak Bases

General Chemistry

17. Acid and Base Equilibrium

pH of Weak Bases

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Multiple Choice

Calculate the pH of a solution that is 0.205 M in CH3NH2 and 0.155 M in CH3NH3Br. Assume the Kb for CH3NH2 is 4.4 x 10^-4.

pH = 8.32

pH = 10.78

pH = 11.22

pH = 9.45

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Verified step by step guidance

Identify the components of the solution: CH3NH2 is a weak base and CH3NH3Br is its conjugate acid. This is a buffer solution.

Use the Henderson-Hasselbalch equation for a buffer solution: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{Base}]}{[\text{Acid}]} \right) \).

Calculate \( \text{pK}_a \) from \( \text{K}_b \) using the relation \( \text{pK}_a + \text{pK}_b = 14 \). First, find \( \text{pK}_b \) by taking the negative logarithm of \( \text{K}_b \): \( \text{pK}_b = -\log(4.4 \times 10^{-4}) \).

Determine \( \text{pK}_a \) by subtracting \( \text{pK}_b \) from 14: \( \text{pK}_a = 14 - \text{pK}_b \).

Substitute \( \text{pK}_a \), the concentration of the base (0.205 M), and the concentration of the acid (0.155 M) into the Henderson-Hasselbalch equation to find the pH.