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 Acids

General Chemistry

17. Acid and Base Equilibrium

pH of Weak Acids

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

Calculate the concentration of the lactate ion in a solution that is 0.100 M in lactic acid (CH₃CH(OH)COOH, pKa = 3.86) and 0.080 M in HCl.

0.180 M

0.020 M

0.100 M

0.080 M

Previous problemNext problem

Verified step by step guidance

Identify the relevant chemical equilibrium: Lactic acid (CH₃CH(OH)COOH) dissociates in water to form lactate ions (CH₃CH(OH)COO⁻) and hydrogen ions (H⁺). The equilibrium expression is: \( \text{CH}_3\text{CH(OH)COOH} \rightleftharpoons \text{CH}_3\text{CH(OH)COO}^- + \text{H}^+ \).

Recognize that HCl is a strong acid and will fully dissociate in solution, contributing additional \( \text{H}^+ \) ions. This will affect the equilibrium position of the lactic acid dissociation.

Use the Henderson-Hasselbalch equation to find the concentration of lactate ions. The equation is: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \([\text{A}^-]\) is the concentration of lactate ions and \([\text{HA}]\) is the concentration of lactic acid.

Calculate the pH of the solution. Since HCl is a strong acid, its concentration (0.080 M) will be the concentration of \( \text{H}^+ \) ions. Use the formula \( \text{pH} = -\log[\text{H}^+] \) to find the pH.

Substitute the known values into the Henderson-Hasselbalch equation to solve for the concentration of lactate ions \([\text{A}^-]\). Rearrange the equation to solve for \([\text{A}^-]\): \( [\text{A}^-] = [\text{HA}] \times 10^{(\text{pH} - \text{pKa})} \).