When a strong base titrant (e.g. NaOH) is added, the following reactions occur: (iv) H2A(aq) + OH(aq) -> H2O(l) + HA-(aq) (v) HA-(aq) + OH(aq) -> H2O(l) + A2-(aq) Note: single arrow to the right rather than double arrow means the reactions go to completion 4. Which region (A,B,C,D,E, or F) is where the titration begins and H2A is the predominant species in solution ? ____________ 5. Which reaction (iv or v) dominates at low pH values? _____________ 6. Halfway through which region (A,B,C,D,E, or F) is where the pH = pKa1 ? ____________
When a strong base titrant (e.g. NaOH) is added, the following reactions occur: (iv) H2A(aq) + OH(aq) -> H2O(l) + HA-(aq) (v) HA-(aq) + OH(aq) -> H2O(l) + A2-(aq) Note: single arrow to the right rather than double arrow means the reactions go to completion 4. Which region (A,B,C,D,E, or F) is where the titration begins and H2A is the predominant species in solution ? ____________ 5. Which reaction (iv or v) dominates at low pH values? _____________ 6. Halfway through which region (A,B,C,D,E, or F) is where the pH = pKa1 ? ____________
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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B. When a strong base titrant (e.g. NaOH) is added, the following reactions occur:
(iv) H2A(aq) + OH(aq) -> H2O(l) + HA-(aq)
(v) HA-(aq) + OH(aq) -> H2O(l) + A2-(aq)
Note: single arrow to the right rather than double arrow means the reactions go to completion
4. Which region (A,B,C,D,E, or F) is where the titration begins and H2A is the predominant species in solution ? ____________
5. Which reaction (iv or v) dominates at low pH values? _____________
6. Halfway through which region (A,B,C,D,E, or F) is where the pH = pKa1 ? ____________
7. Explain your answer to #6 in terms of the Henderson-Hasselbalch equation.
8. Which species (H2A, HA-, or A2-) predominates at "C", the equivalence point 1 ?
9. During the titration, which region (A,B,C,D,E, or F) on the curve represents the first buffer region? _____________ ? Second buffer region _____________ ?
10. Halfway through the second buffer (region "D"), the pH = pKa2. What is the value of pKb1 ? (Use the relationship that pKa2 + pKb1 = 14 )
![## H₂A Titration Curve (with Strong Base)
### Titration Curve Description
The image features a titration curve graph on the left side that depicts the titration of a diprotic acid (H₂A) with a strong base. The graph has:
- **Y-Axis:** Represents pH, ranging from 2 to 14.
- **X-Axis:** Represents the volume of titrant added, ranging from 0 to 35 mL.
Key points on the curve:
- **A:** Initial point at low pH.
- **B and D:** Buffer regions showing gradual pH increase.
- **C:** A steep rise indicating the first equivalence point, where the first proton is completely titrated.
- **E:** Another steep rise indicating the second equivalence point, where the second proton is fully titrated.
- **F:** Final point at high pH, with the curve leveling off.
### Henderson-Hasselbalch Equations
Displayed on the right are the Henderson-Hasselbalch equations:
1. \( \text{pH} = \text{pK}_1 + \log \left( \frac{[\text{HA}^-]}{[\text{H}_2\text{A}]} \right) \)
2. \( \text{pH} = \text{pK}_2 + \log \left( \frac{[\text{A}^{2-}]}{[\text{HA}^-]} \right) \)
Important notes:
- Both equations are **always true**.
- A solution has only one pH value at a given time.
- The choice of equation depends on known concentrations:
- Use the first equation when [H₂A] and [HA⁻] are known.
- Use the second equation when [HA⁻] and [A²⁻] are known.
This detailed explanation is intended to guide students in understanding the principles of acid-base titration and the application of the Henderson-Hasselbalch equations to calculate pH at different stages of the titration process.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F3129c971-f425-413a-93d6-6547672e04e6%2F1674b4e4-3b9f-449e-bd4a-2ace74600767%2Fxubpz2i_processed.png&w=3840&q=75)
Transcribed Image Text:## H₂A Titration Curve (with Strong Base)
### Titration Curve Description
The image features a titration curve graph on the left side that depicts the titration of a diprotic acid (H₂A) with a strong base. The graph has:
- **Y-Axis:** Represents pH, ranging from 2 to 14.
- **X-Axis:** Represents the volume of titrant added, ranging from 0 to 35 mL.
Key points on the curve:
- **A:** Initial point at low pH.
- **B and D:** Buffer regions showing gradual pH increase.
- **C:** A steep rise indicating the first equivalence point, where the first proton is completely titrated.
- **E:** Another steep rise indicating the second equivalence point, where the second proton is fully titrated.
- **F:** Final point at high pH, with the curve leveling off.
### Henderson-Hasselbalch Equations
Displayed on the right are the Henderson-Hasselbalch equations:
1. \( \text{pH} = \text{pK}_1 + \log \left( \frac{[\text{HA}^-]}{[\text{H}_2\text{A}]} \right) \)
2. \( \text{pH} = \text{pK}_2 + \log \left( \frac{[\text{A}^{2-}]}{[\text{HA}^-]} \right) \)
Important notes:
- Both equations are **always true**.
- A solution has only one pH value at a given time.
- The choice of equation depends on known concentrations:
- Use the first equation when [H₂A] and [HA⁻] are known.
- Use the second equation when [HA⁻] and [A²⁻] are known.
This detailed explanation is intended to guide students in understanding the principles of acid-base titration and the application of the Henderson-Hasselbalch equations to calculate pH at different stages of the titration process.
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