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 Acid-Strong Base

General Chemistry

18. Aqueous Equilibrium

Titrations: Weak Acid-Strong Base

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Multiple Choice

Suppose 40.0 mL of an acetic acid solution of unknown concentration is titrated with 0.100 M NaOH. After 20.0 mL of the base solution has been added, the pH in the titration flask is 5.10. What was the concentration of the original acetic acid solution?

0.025 M

0.050 M

0.075 M

0.100 M

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Verified step by step guidance

Start by writing the balanced chemical equation for the reaction between acetic acid (CH₃COOH) and sodium hydroxide (NaOH): CH₃COOH + NaOH → CH₃COONa + H₂O.

Determine the moles of NaOH added using the formula: \( \text{moles of NaOH} = \text{volume (L)} \times \text{molarity (M)} \). Convert 20.0 mL to liters and multiply by 0.100 M.

Since the reaction is a 1:1 stoichiometry, the moles of NaOH added equals the moles of acetic acid that have reacted. Use this information to find the moles of acetic acid initially present.

Use the Henderson-Hasselbalch equation to relate the pH to the concentration of acetic acid and its conjugate base: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \). Given \( \text{pH} = 5.10 \) and \( \text{pK}_a \approx 4.76 \) for acetic acid, solve for the ratio \( \frac{[\text{A}^-]}{[\text{HA}]} \).

Calculate the initial concentration of acetic acid using the moles of acetic acid and the initial volume of the solution (40.0 mL converted to liters). This will give you the concentration of the original acetic acid solution.