Using the lab
top pH meter:
The instrument used in this activity
was a AB15 Fisher Scientific pH meter, but there are many good models
available. The most important consideration for the use of pH meters is
proper calibration for standardization of the measurements. Using
buffers of known pH, the readings of the meter must be set to reflect those
of the buffers. Read the instruction manual carefully and remember
to clean the electrode with distilled water after each reading.
 
Instructions for use:
1. Place the probe in mystery solution #1 and read the pH meter after it
stabilizes.
2. Rinse the probe with distilled water after testing the solution.
3. Repeat these steps for mystery solutions #2 and #3.
4. The pH of each mystery solution may also be measured by using a handheld
portable pH meter or pH paper.
5. Record the data for the three methods in a data table to compare the pH
readings. Which do think is more accurate?
6. Use the pH of the solution, the pH scale below, and other observations to
hypothesize what the unknown solutions are.
pH Scale
|
|
[H+] |
pH |
Example |
| Acids |
1 X 100 |
0 |
HCl |
| 1 x 10-1 |
1 |
Stomach acid |
| 1 x 10-2 |
2 |
Lemon juice |
| 1 x 10-3 |
3 |
Vinegar |
| 1 x 10-4 |
4 |
Soda |
| 1 x 10-5 |
5 |
Rainwater |
| 1 x 10-6 |
6 |
Milk |
| Neutral |
1 x 10-7 |
7 |
Pure water |
| Bases |
1 x 10-8 |
8 |
Egg whites |
| 1 x 10-9 |
9 |
Baking Soda |
| 1 x 10-10 |
10 |
Tums® antacid |
| 1 x 10-11 |
11 |
Ammonia |
| 1 x 10-12 |
12 |
Mineral Lime - Ca(OH)2 |
| 1 x 10-13 |
13 |
Drano® |
| 1 x 10-14 |
14 |
NaOH |
Links to suggested web sites:
University of British Colombia - Chemistry Department
Access Excellence
Online Biology Book-
Properties of Water
|
And always remember. . .
"With just a pinch of acid and a little bit of titration,
you too can get to first base!"
|
 |
Biochemically Yours,
Martha, Lyn, Dwight, & Chris, the JUST-A-LITTLE-OFF-BASE gang
|
