CHEM 104 LAB 5
Notebook
Experiment #: 5
Title: Buffers
Purpose: To study buffers (solutions that resist pH change) by observing what happens when a solution is not buffered, and how pH effects enzymes.
Procedure:
- Add a scoop of sodium acetate trihydrate to both the water and the buffer. Record pH changes.
- Add a few drops of HCl to each water and buffer solution. Record pH changes.
- Measure out 50 ml of sodium lactate (base) and mix with 50 ml of lactic acid (acid) in beaker.
- Measure pH, which will equal pKa at equal concentrations of acid and base.
- Create 6 tubes with different buffers that creates a different pH environment.
- Add ONPG with automatic pipette into each tube and stir, leave for 4 minutes
- Add sodium carbonate base, put in spectrophotometer (absorbance 420 nm)
- Record detection of absorption
Data/Results/Calculations:
H2O (l) + HA(aq) <-> H3O+(aq) + A-(aq) Ka = [H3O+][A-]/[HA]
Addition of:
Base: OH- + HA <-> H2O (l) + A (aq)
Acid: H3O+(aq) + A-(aq) <-> HA(aq) + H2O(l)
Acetate (weak acid): C2H3O2- (aq)+ H2O (l) <-> HC2H3O2(aq) + OH-
(aq) Fe3+ (or HCl): [Fe(H2O)63+ +H2O (l) <-> [Fe(H2O)5OH]2+(aq) +
H3O+(aq)
H2O (l) + HA(aq) <-> H3O+(aq) + A-(aq)
pH for lactic acid:
pH = pKa + log [base]/[acid] pH = 3.85 + log [0.07]/[0.03] = 4.22 pH = 3.85 + log[0.03]/[0.07] = 3.48
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