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.