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

Previous problemNext problem

Struggling with General Chemistry?

Join thousands of students who trust us to help them ace their exams!Watch the first video

Multiple Choice

Caffeine (C8H10N4O2) is a weak base with a pKb of 10.4. Calculate the pH of a solution containing a caffeine concentration of 435 mg/L.

pH = 7.0

pH = 5.2

pH = 8.6

pH = 9.8

Previous problemNext problem

Verified step by step guidance

Convert the concentration of caffeine from mg/L to mol/L. First, calculate the molar mass of caffeine (C8H10N4O2) by adding the atomic masses of its constituent elements: Carbon (C), Hydrogen (H), Nitrogen (N), and Oxygen (O).

Use the molar mass to convert the given concentration from mg/L to mol/L. This is done by dividing the mass concentration (in mg/L) by the molar mass (in g/mol) and converting mg to g.

Recognize that caffeine is a weak base and use the given pKb value to find the Kb (base dissociation constant) using the formula: Kb = 10^(-pKb).

Set up an equilibrium expression for the dissociation of caffeine in water: C8H10N4O2 + H2O ⇌ C8H10N4O2H+ + OH-. Use an ICE table (Initial, Change, Equilibrium) to express the concentrations of the species at equilibrium.

Solve for the hydroxide ion concentration [OH-] using the Kb expression: Kb = [C8H10N4O2H+][OH-] / [C8H10N4O2]. Then, calculate the pOH from [OH-] and use the relationship pH + pOH = 14 to find the pH of the solution.