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

Determine the pH of a solution that is 0.125 M in CO3^2−. For carbonic acid (H2CO3), Ka1=4.3×10^−7 and Ka2=5.6×10^−11. What is the pH of the solution?

pH = 13.00

pH = 9.25

pH = 7.00

pH = 11.37

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Verified step by step guidance

Identify the relevant chemical species and equilibria: In this problem, we are dealing with carbonate ion (CO3^2−) in solution, which can undergo hydrolysis to form bicarbonate (HCO3^−) and hydroxide ions (OH^−). The relevant equilibria are CO3^2− + H2O ⇌ HCO3^− + OH^−.

Use the equilibrium constant for the hydrolysis reaction: The equilibrium constant for the hydrolysis of CO3^2− can be derived from the second dissociation constant of carbonic acid (Ka2) and the ion product of water (Kw). The expression is Kb = Kw / Ka2, where Kw = 1.0 × 10^−14.

Set up the equilibrium expression: For the hydrolysis reaction, the equilibrium expression is Kb = [HCO3^−][OH^−] / [CO3^2−]. Assume that the initial concentration of CO3^2− is 0.125 M and that the change in concentration due to hydrolysis is x, so [HCO3^−] = x and [OH^−] = x.

Solve for x using the equilibrium expression: Substitute the known values into the equilibrium expression to solve for x, which represents the concentration of OH^− ions in the solution. This involves solving the equation Kb = x^2 / (0.125 - x).

Calculate the pH: Once you have the concentration of OH^− ions, calculate the pOH using the formula pOH = -log[OH^−]. Then, convert pOH to pH using the relationship pH + pOH = 14. This will give you the pH of the solution.