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

18. Aqueous Equilibrium

Titrations: Weak Base-Strong Acid

General Chemistry

18. Aqueous Equilibrium

Titrations: Weak Base-Strong Acid

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Multiple Choice

Consider the titration of a 26.0-mL sample of 0.185 M CH3NH2 (Kb=4.4×10⁻⁴) with 0.155 M HBr. What is the pH after adding 6.0 mL of HBr?

4.75

5.28

6.02

7.00

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Verified step by step guidance

Calculate the initial moles of CH3NH2 using the formula: moles = concentration × volume. Convert the volume from mL to L before calculating.

Calculate the moles of HBr added using the same formula: moles = concentration × volume. Again, ensure the volume is in liters.

Determine the moles of CH3NH2 and HBr that react. Since HBr is a strong acid and CH3NH2 is a weak base, they will react in a 1:1 ratio to form CH3NH3+ and Br-. Subtract the moles of HBr from the initial moles of CH3NH2 to find the moles of CH3NH2 remaining.

Calculate the concentration of CH3NH3+ formed and the remaining CH3NH2 in the solution. Use the total volume of the solution (initial volume of CH3NH2 + volume of HBr added) to find these concentrations.

Use the Henderson-Hasselbalch equation to find the pH of the solution: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right) \). First, calculate \( \text{pK}_a \) from \( \text{pK}_b \) using the relation \( \text{pK}_a + \text{pK}_b = 14 \). Then, substitute the concentrations of CH3NH2 (base) and CH3NH3+ (acid) into the equation to find the pH.