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

A 30.00-mL sample of 0.125 M HCOOH is being titrated with 0.175 M NaOH. What is the pH after 11.2 mL of NaOH has been added? Ka of HCOOH = 1.8 × 10⁻⁴

pH = 4.25

pH = 3.75

pH = 5.00

pH = 6.50

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Verified step by step guidance

Step 1: Calculate the initial moles of HCOOH in the solution. Use the formula \( \text{moles} = \text{volume} \times \text{molarity} \). For HCOOH, \( \text{moles} = 30.00 \text{ mL} \times 0.125 \text{ M} \). Convert the volume from mL to L by dividing by 1000.

Step 2: Calculate the moles of NaOH added using the same formula \( \text{moles} = \text{volume} \times \text{molarity} \). For NaOH, \( \text{moles} = 11.2 \text{ mL} \times 0.175 \text{ M} \). Again, convert the volume from mL to L.

Step 3: Determine the moles of HCOOH that react with NaOH. Since NaOH is a strong base, it will react completely with HCOOH. Subtract the moles of NaOH from the initial moles of HCOOH to find the moles of HCOOH remaining.

Step 4: Calculate the moles of the conjugate base, HCOO⁻, formed. The moles of HCOO⁻ will be equal to the moles of NaOH added, as each mole of NaOH reacts to form one mole of HCOO⁻.

Step 5: Use the Henderson-Hasselbalch equation to find the pH. The equation is \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \( \text{pKa} = -\log(\text{Ka}) \). Calculate \( \text{pKa} \) using the given \( \text{Ka} \) value, and then plug in the concentrations of HCOO⁻ and HCOOH to find the pH.