Transcript Buffering Capacity

Michel Lotito
(6/15/50-6/25/07)
Monsieur Mangetout
“Mr. Eat-Everything”
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
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
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
PURPOSE
• To evaluate and compare the relative
buffering capacity of seven organic and
inorganic substances through calculation
of ΔpH (change in pH)
Seven Potential Buffers
Albumin
Casein
Magnesium Hydroxide
Sodium Bicarbonate
Sodium Chloride
Sodium Stearate
Water
Albumin
• Protein found in
egg whites
• Comprised of
amino acids which
have a positive and
negative functional
groups
Casein
• Protein found in
mammalian milk
• Contains a water
repelling core and
polar/charged tails
Magnesium Hydroxide
• Active ingredient in
Milk of Magnesia
• An strong
electrolyte,
meaning rapid
disassociation into
ions
Sodium Bicarbonate
• Baking soda
• Disassociates into
two charged ions,
sodium (+) and
bicarbonate (-)
Sodium Chloride
• Table Salt
• Inorganic
substance with
weak ionic bonding
Sodium Stearate
• Key ingredient of
soap
• Found in non-polar
fats and oils
Water
• Amphoteric = may
serve as an acid or
a base when in
solution
• Neutral pH
Buffering Capacity Protocol
1. Place 25mL of your
first buffer into each of
two beakers
2. Remove storage
bottles from pH probes
and immerse tip of
probe in beaker.
Record the initial pH in
table 2
3. To the left beaker, add
5 drops 0.1M HCl
4. To the right beaker, 5
drops 0.1M NaOH
5. Record the pH for each
probe in table 2
6. Repeat steps 3-5 until
a total of 30 drops of
acid and base have
been added to their
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 ΔpH , ΔpH and ΔpH
• Post your data on the board in the front of
the room
acid
base
total
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.