1. Michel Lotito (6/15/50-6/25/07)

2. Monsieur Mangetout “Mr. Eat-Everything”

5. Homeostatic Connections To pH
Carbon dioxide sensors in carotid artery measure blood pH and tell brain when to signal lungs to breathe
Absorption and digestion require specific pH
pH may prohibit parasitic infections
Changes in pH may alter or destroy enzymes

6. How Is pH Maintained?
Body is slightly alkaline, but ranges from pH 2 to pH 11 in matter of centimeters
Excess hydronium and hydroxide ions must be neutralized
BUFFERS resist changes in pH

7. What Are Buffers And How Do They Work?
Substances that resist changes in pH
Buffers are themselves weak acids and/or bases
These weak acids and/or bases disassociate in solution, neutralizing the excess hydronium (H+)or hydroxide (OH-) ions
As the excess H+ and OH- ions are no longer “free”, their concentration does not effectively increase; pH stays the same

8. PURPOSE
To evaluate and compare the relative buffering capacity of seven organic and inorganic substances through calculation of ΔpH (change in pH)

9. Seven Potential Buffers
Albumin
Casein
Magnesium Hydroxide
Sodium Bicarbonate
Sodium Chloride
Sodium Stearate
Water

10. Albumin Protein found in egg whites
Comprised of amino acids which have a positive and negative functional groups

11. Casein Protein found in mammalian milk
Contains a water repelling core and polar/charged tails

12. Magnesium Hydroxide Active ingredient in Milk of Magnesia
An strong electrolyte, meaning rapid disassociation into ions

13. Sodium Bicarbonate Baking soda
Disassociates into two charged ions, sodium (+) and bicarbonate (-)

14. Sodium Chloride
Table Salt
Inorganic substance with weak ionic bonding

15. Sodium Stearate Key ingredient of soap
Found in non-polar fats and oils

16. Water Amphoteric = may serve as an acid or a base when in solution
Neutral pH

17. Buffering Capacity Protocol
Place 25mL of your first buffer into each of two beakers
Remove storage bottles from pH probes and immerse tip of probe in beaker. Record the initial pH in table 2
To the left beaker, add 5 drops 0.1M HCl
To the right beaker, 5 drops 0.1M NaOH
Record the pH for each probe in table 2
Repeat steps 3-5 until a total of 30 drops of acid and base have been added to their respective beakers

18. Protocol Part 2
Discard the water-acid and water-base mixtures from the first experiment and rinse the beakers
Obtain 25mL of the next assigned buffer for each of the two beakers
Repeat the first protocol up to 30 drops of acid & base respectively, recording the pH values in table 1
Calculate the ΔpHacid, ΔpHbase and ΔpHtotal
Post your data on the board in the front of the room

19. Calculating Buffering Capacity
To calculate ΔpHacid and ΔpHbase for a buffer, find the absolute value of the difference between the initial (0 drops) and final (30 drops) values for both probes. Record these values in table 1.
To determine and then rank the buffering capacities, calculate the ΔpHtotal by adding the ΔpHacid and ΔpHbase . Record these values in table 1.
For water’s buffering capacity, use the data you collected in the Acids, Bases & Indicators lab.