March 15th Part I
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Acids, Bases, pH, Buffer Notes
Acids, Bases video
Lab 7: Acids, Bases, pH and Buffers
Acids and Bases Handout
Break
Acids and Bases
Chapter 2 pp. 39-41
Also pp. 1008-1010
Oxygen (O)
(8p+,8n0,8e-)
2 electrons + 6
electrons
3
Special Properties of Water
4
What is pH?
• A scale from the range of 0 – 14
• 7.0 represents neutral
• Lower than 7 is acid
• Higher than 7 is alkaline
• Measurement scale is logarithmic
pH is the concentration of H+
– More H+ the lower the pH or more acid
– Less H+ the higher the pH or more alkaline
5
The pH Scale
Acid and Base
6
Note that each
decrease in pH by
one pH unit means
a tenfold increase
in the
concentration of
hydrogen ions.
Note that each
increase in pH by
one pH unit
means a tenfold
decrease in the
concentration of
hydrogen ions.
pH SCALE
0
7
14
acid
neutral
alkaline
High
H+,
Low
pH
Low
H+,
High
pH
7
Hydrogen
Hydrogen ion
H
H+
8
Fig. 2.13 in text
As the Hydrogen ion
concentration increases,
the Hydroxyl ion
concentration decreases
9
Neutralization
• Mixing acids and bases
• Displacement reaction to form a water and
a salt
• HCL + NaOH
NaCl + H20
DISSOCIATION OF NaCl
11
Hydrochloric Acid (Strong
Acid)
Carbonic acid
(Weak Acid)
12
Strong vs. Weak Acids
• Weak Acids
– Carbonic Acid: H2CO3
– Do not dissociate completely in water
– Do not change pH
– Important in buffer systems (tie up OH- ions)
• Strong Acids
– Hydrochloric Acid: HCL
– Dissociate completely and irreversibly in
water
– Dramatically change pH of a solution
Strong vs. Weak Bases
• Weak Bases
– Sodium Bicarbonate: NaHCO3
– Do not dissociate completely in water
– Do not change pH
– Important in buffer systems (tie up H+ ions)
• Strong Bases
– Sodium Hydroxide: NaOH
– Dissociate completely and irreversibly in
water
– Dramatically change pH of a solution
EQUILIBRIUM
A
+
B
AB
15
Buffers resist abrupt changes in pH
Buffers release H+ as pH rises
They bind H+ when pH decreases
Acidity only reflects FREE hydrogen ions (H+) not when
they are bound to anions.
STRONG
ACID
WEAK ACID
STRONG
BASE
HCl
H+
+
Cl-
HAc
H+
+
Ac-
NaOH
Na+
+
OH-
OH- + H+ = H2O
16
THE BICARBONATE ION
The most important single buffer in human blood is the bicarbonate ion
Bicarbonate, HCO3-, is in equilibrium with H2CO3 (carbonic acid) as follows:
Response to rise in pH
HC03- + H+
H2CO3
Response to drop in pH
17
Buffers protect against shifts in pH
Bicarbonate buffer system
Response to a rise in pH
HCO3-
H2CO3
Carbonic acid
HCO3-
H+
+
bicarbonate
+
H+
H2CO3
bicarbonate
Response to a drop in pH
H2CO3
Carbonic acid
H2O +
CO2
Carbonic acid
18
19
Range of Arterial pH Values
ACIDOSIS
pH = 1 to 7.40
ACIDOSIS
lower than 7.0
NEUTRAL
pH = 7.41
ALKALOSIS
pH = 7.42 to 14.0
ALKALOSIS
higher than 7.8
20
Normal Balance Between Acid
and Base
Faucet and Drain Analogy
• The blood's pH is normally between 7.35
and 7.45.
• The body's goal is a constant balance
between incoming/produced acids and
bases (faucet on) and eliminated acids
and bases (drain open).
• Imbalances lead to acidosis or alkalosis
(acid or base overflow in the sink)
• How can the balance be maintained ?
Any disease or
condition that affects the lungs,
kidneys, metabolism or
breathing has the potential to
cause acidosis or alkalosis.
Causes of Acidosis
• Increased acid production within the body
• Consumption of substances that are
metabolized to acids,
• Decreased acid excretion,
• Increased excretion of base.
Causes of Alkalosis
• Electrolyte disturbances
– prolonged vomiting or severe dehydration,
– administration or consumption of base,
– Hyperventilation (increased CO2 production
changes the pH)
Effects of Acidosis and Alkalosis
• Alkalosis (pH above 7.8)
– Overexcited nervous system
– Muscle tetany
– Nervousness
– Convulsions
– Death from respiratory arrest
• Acidosis (pH below 7.0)
– Depressed nervous system
– Coma and Death
Homeostasis of Acid-Base
Balance
• Kidneys and Lungs
• Chemical Systems
– Blood Buffers include:
•
•
•
•
Hemoglobin
Bicarbonate
Phosphates
Plasma Proteins
pH and H+ concentrations of Body Fluids
H+ concentration
(mEq/L)
pH
Arterial blood
4.0 x 10 -5
7.41
Venous blood
4.5 x 10 -5
7.35
Interstitial fluids
4.5 x 10 -5
7.35
Intracellular
fluids
Urine
1 x 10-3 to 4 x 10 -5
6.0 to 7.4
3 x 10-2 to 1 x 10 -5
4.5 to 8.0
Gastric HCl
160
0.8
29
More on Acid-Base Balance
• Text pp. 1008-1010
– Chemical Buffering Systems
• Bicarbonate
• Phosphate
• Protein
Buffer Lab
• Objectives:
– Understand how buffers work and determine
the optimal buffering range for specified
buffers
– Understand the role buffer concentration
plays in maintaining pH
Lab # 7
• Exercise I
– Determination of pH
• Exercise II
– Analysis of different buffers
– Part I: Buffer an Acid
– Part II: Buffer a Base
– Group 1 will test deionized water, 100 mM
Acetate Buffer and 100 mM Glycine Buffer
– Group 2 will test different buffer
concentrations