A buffer is a solution that maintains a constant pH, regardless of the addition of strong acids or strong bases as long as the amount of acid or base added is within the buffering capacity of the solution.
A buffer must contain the conjugate acid or base pair of a weak acid or weak base.
The common ion effect is when a given ion is added to a mixture at equilibrium that already contains the given ion. This causes the equilibrium to shift away from forming more of that ion.
The Henderson-Hasselbalch equation is used to calculate pH using the pKa and the acid to conjugate base ratio. This equation can be used to calculate the pH of a buffered solution or determine the amount of conjugate acid or base needed to prepare a buffer at a specific pH value.
The buffer capacity is a measure of the buffer's ability to resist changes in pH. If the concentration of acid or base is lower than the concentration of the buffer components, the pH value will resist drastic changes. Once these concentrations are exceeded, the buffer effect of the solution will no longer function, causing drastic changes in the pH.
Source: Smaa Koraym at Johns Hopkins University, MD, USA
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.
1 Stir plate |
1 Lab stand with thermometer clamp |
1 pH meter |
1 Handheld spectrophotometer |
2 Calibration buffers |
2 400-mL beakers |
2 100-mL beakers |
1 25-mL beaker |
1 50-mL graduated cylinder |
2 10-mL graduated cylinders |
1 Small watch glass |
1 Magnetic stir bar |
1 Funnel |
1 Forceps |
1 Plastic wash bottle |
1 250- or 500-mL capped polyethylene bottle |
1 Roll of laboratory tape |
2 Plastic pipettes |
1 Labeling pen |
1 Box of laboratory wipes |
1 1-mL micropipette with tips |
1 200-µL micropipette with tips |
10 1.5-mL cuvettes with caps |