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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![**3. Describe how you would prepare a 500.0-mL of a 0.500 M HEPES buffer (FW = 238.3 g/mol, pKₐ = 7.50).**
To prepare a 500.0-mL solution of 0.500 M HEPES buffer, you need to follow these steps:
1. **Calculate the mass of HEPES needed**:
- Use the formula:
\[
\text{mass} = \text{molarity} \times \text{volume (L)} \times \text{formula weight (FW)}
\]
- Plug in the given values:
\[
\text{mass} = 0.500 \, \text{M} \times 0.500 \, \text{L} \times 238.3 \, \text{g/mol} = 59.575 \, \text{g}
\]
- Weigh out 59.575 grams of HEPES.
2. **Dissolve the HEPES**:
- Add the weighed HEPES to a beaker or flask.
- Add a portion of distilled water (less than 500 mL) and stir until the HEPES is fully dissolved.
3. **Adjust the pH (if necessary)**:
- HEPES buffers have a pKₐ of 7.50, which makes them suitable for buffering around that pH.
- Use a pH meter to measure the pH of your solution.
- If the pH needs adjustment, add small amounts of HCl or NaOH to reach the desired pH level.
4. **Make up the final volume**:
- Once the pH is adjusted, transfer the solution to a 500-mL volumetric flask.
- Add distilled water up to the 500-mL mark to ensure accurate volume.
5. **Mix the solution thoroughly**:
- Invert or stir the flask to ensure the buffer is uniformly mixed.
This procedure will yield 500.0 mL of a 0.500 M HEPES buffer ready for use in laboratory applications.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fe7417eb4-c4f6-4b23-b299-1f887648c283%2F08450539-fd1d-4586-a7ee-8c78347580d8%2Fxls7qam_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**3. Describe how you would prepare a 500.0-mL of a 0.500 M HEPES buffer (FW = 238.3 g/mol, pKₐ = 7.50).**
To prepare a 500.0-mL solution of 0.500 M HEPES buffer, you need to follow these steps:
1. **Calculate the mass of HEPES needed**:
- Use the formula:
\[
\text{mass} = \text{molarity} \times \text{volume (L)} \times \text{formula weight (FW)}
\]
- Plug in the given values:
\[
\text{mass} = 0.500 \, \text{M} \times 0.500 \, \text{L} \times 238.3 \, \text{g/mol} = 59.575 \, \text{g}
\]
- Weigh out 59.575 grams of HEPES.
2. **Dissolve the HEPES**:
- Add the weighed HEPES to a beaker or flask.
- Add a portion of distilled water (less than 500 mL) and stir until the HEPES is fully dissolved.
3. **Adjust the pH (if necessary)**:
- HEPES buffers have a pKₐ of 7.50, which makes them suitable for buffering around that pH.
- Use a pH meter to measure the pH of your solution.
- If the pH needs adjustment, add small amounts of HCl or NaOH to reach the desired pH level.
4. **Make up the final volume**:
- Once the pH is adjusted, transfer the solution to a 500-mL volumetric flask.
- Add distilled water up to the 500-mL mark to ensure accurate volume.
5. **Mix the solution thoroughly**:
- Invert or stir the flask to ensure the buffer is uniformly mixed.
This procedure will yield 500.0 mL of a 0.500 M HEPES buffer ready for use in laboratory applications.
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