Biology Notes: pH and Buffers
pH:

Acidic solutions:

Basic solutions:
pH scale:
http://www.youtube.com/watch?v=V-iQKuNFME8&NR=1
pH and Living Systems:

Homeostasis/Equilibrium:

Buffer:
1.
2.
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/buffer12.swf
Effects of pH Imbalance in Living Systems
 Blood:

Urine:
Biology Lab: How Do Biological Materials Respond to Acids and Bases? Name: ____________________
Purpose To study the response of biological materials to acids and bases.
Materials
pH paper or probes
scissors
250ml beakers
25ml-graduated cylinder
various homogenates (potato, celery, mushroom, yeast, liver, or egg white)
Alka Seltzer solution
0.1M NaOH
0.1M HCl
Assigned solutions: ___________________________________________________________________
Procedure
1. Pour 25ml of your assigned liquid into the 250ml beaker.
2. Measure the pH of the substance using the pH probe/strip. Record data in Data Table1.
3. Add 5 drops of HCl (Hydrochloric acid), making sure to add one drop at a time and swirling after each drop.
After you have added 5 drops, measure the pH again. Record data in Data Table 1.
4. Follow the same procedure as in #3, by adding 5 more drops. Up to this point 10 drops have been added to
the solution. Measure the pH. Record data in Data Table 1.
5. Add 5 more drops. Record data under 15 drops in Data Table 1.
6. Add 5 more drops. Record data under 20 drops in Data Table 1.
7. Add 5 more drops. Record data under 25 drops in Data Table 1.
8. Add 5 more drops. Record data under 30 drops in Data Table 1.
9. Rinse the beaker well with water and add another 25ml of same assigned solution.
10. Follow steps #2-8, BUT this time add drops of NaOH and record your data in Table 2. It is on the back of this
sheet.
Data Table 1: The pH of various homogenates after adding HCl
10 drops
15 drops
Initial pH
5 drops
HCl
HCl
HCl
Tap Water
Alka Seltzer
Potato
Egg White
Yeast
Celery
Liver
Mushroom
20 drops
HCl
25 drops
HCl
30 drops
HCl
Table 2: The pH of various homogenates after adding NaOH
Initial pH
5 drops
10 drops
NaOH
NaOH
15 drops
NaOH
20 drops
NaOH
25 drops
NaOH
30 drops
NaOH
Tap Water
Alka Seltzer
Potato
Egg White
Yeast
Celery
Liver
Mushroom
Analysis
1. Graph your results in Excel. You will have two graphs, one from the data in Table 1 and the other from Table
2. Include all of your results in one graph using different colors for each material. Follow the directions on
the provided handout or online.
2. Examine your graphs. Compare the following
a. Which homogenates (Alka seltzer, potato, egg white, yeast, celery, liver, or mushroom) was most similar
to the water? Compare the lines on the graph.
b. Explain what this means.
c. Which homogenates (alka seltzer, potato, egg white, yeast, celery, live, or mushroom) was most similar to
the pH= 7? Compare the lines on the graph.
d. Explain what this means.
3. Which of your homogenates has the most buffering capacity? How did you determine this? Explain.
4. What did you learn about the ability of living systems to regulate pH? Explain their importance.