CHEM 104 LAB
5 Notebook
Experi
ment #:
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:
1. Add a scoop of sodium acetate trihydrate to both the water and the buffer. Record
pH changes.
2. Add a few drops of HCl to each water and buffer solution. Record pH changes.
3. Measure out 50 ml of sodium lactate (base) and mix with 50 ml of lactic acid (acid) in
beaker.
4. Measure pH, which will equal pKa at equal concentrations of acid and base.
5. Create 6 tubes with different buffers that creates a different pH environment.
6. Add ONPG with automatic pipette into each tube and stir, leave for 4 minutes
7. Add sodium carbonate base, put in spectrophotometer (absorbance 420 nm)
8. 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)
