1. Acids, Bases, pH and Buffers

2. The pH of a solution tells us if it is acidic, basic or neutral
pH=-log[H+]
The pH of a solution tells us if it is acidic, basic or neutral

3. pH indicator
A pH indicator is a substance that, when a small amount of it is added to a solution of unknown pH, will change its color.
This is a way to determine pH of a solution visually.
The indicator used in this lab will be obtained from a natural source, red cabbage.
Cabbage indicator produces a particular color depending on the pH of the solution.

4. Buffers Buffers maintain the pH ([H+]) of a solution
Example blood must be maintained between pH =
Buffers can work as both an acid or a base so they can neutralize small amounts of acid and base
pH of blood is maintained by bicarbonate HCO3-
HCO3- + H+  H2CO3
HCO3- + OH-  H2O + CO32-
In this experiment we will study the effect of an acid and base on a buffer and compare it with a non-buffer
The buffering capacity of a solution is tested by adding small amounts of acid (for example, HCl) and base (for example, NaOH) and checking the pH after each addition. If the pH changes only slightly, the solution is a good buffer. Eventually its buffering capacity will be exhausted, however, and the pH will change dramatically.

5. pH color using red cabbage indicator
14 test tubes arranged in a rack
Pour 3-4mL of of each buffer into a separate test tube
label the pH of each buffer on each test tube
Add 2-3 mL of the red cabbage indicator to each test tube and describe the color of each
Keep as a reference

6. Measuring pH
Label 10 large test tubes with each household item to be tested and predict if you think the solution will be Acidic, Basic, or Neutral.
3 mL, (60 drops), of the samples (shampoo, conditioner, mouthwash, detergents, fruit juice, aspirin etc) into the labeled test tube
Add 3 mL, (60 drops), of the red cabbage solution and estimate the pH from the color
Determine the pH by comparing with the 14 test tubes to find the color that most closely matches your sample

7. Acetic Acid/Sodium Acetate
Buffers
Test tube #
Contents of test tube
60 drops
indicator
What to add
10 drops 1
Water
cabbage
HCl 2
NaOH 3
Acetic Acid/Sodium Acetate 4 5
pH 2 buffer
Label 5 large test tubes
To 2 test tubes add 60 drops of DI water and 60 drops of cabbage indicator
To 3 test tubes add 60 drops of the Acetic Acid/Sodium Acetate buffer and 60 drops of cabbage indicator
Record the initial pH
Then add 10 drops of either HCl, NaOH or the pH 2 buffer according to the table