The question
Name: ______________________ Date: ____________ Preparing a buffer of a chosen pH (4 points)
Data table
Weak acids available
A student must prepare 500.0 mL of a buffer with pH 3.50 in which the concentration of the weak acid is 0.200 M. The weak acids below and the sodium salt of each conjugate base are available, together with standard lab glassware.
| Weak acid | pKa | Sodium salt | Molar mass of salt (g/mol) |
|---|---|---|---|
| Formic acid, HCOOH | 3.74 | HCOONa | 68.01 |
| Acetic acid, CH₃COOH | 4.74 | CH₃COONa | 82.03 |
| Dihydrogen phosphate, H₂PO₄⁻ | 7.21 | Na₂HPO₄ | 141.96 |
(a) Identify the best weak acid for this buffer. Justify your choice. [1 point]
(b) Calculate the mass of the sodium salt the student must dissolve. [2 points]
(c) Describe how the student should prepare the buffer, naming the glassware. [1 point]