Download - March 15 th Part I
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March 15th Part I
• Return Papers
• Acids, Bases, pH, Buffer Notes
• Acids, Bases video
• Lab 7: Acids, Bases, pH and Buffers
• Acids and Bases Handout
• Break
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Acids and Bases
Chapter 2 pp. 39-41
Also pp. 1008-1010
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Oxygen (O)
(8p+,8n0,8e-)
2 electrons + 6 electrons
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Special Properties of Water
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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
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The pH Scale
Acid and Base
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pH SCALE
0 7 14
acid alkalineneutral
High H+, Low
pH
Low H+, High pH
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.
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Hydrogen ionHydrogen
H H+
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Fig. 2.13 in text
As the Hydrogen ionconcentration increases, the Hydroxyl ion concentration decreases
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Neutralization
• Mixing acids and bases
• Displacement reaction to form a water and a salt
• HCL + NaOH NaCl + H20
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DISSOCIATION OF NaCl
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Hydrochloric Acid (Strong Acid)
Carbonic acid (Weak Acid)
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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
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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
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EQUILIBRIUM
A + B AB
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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.
HCl H+ + Cl-
HAc H+ + Ac-
STRONG ACID
WEAK ACID
NaOH Na+ + OH-STRONG BASE
OH- + H+ = H2O
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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:
H2CO3 HC03- + H+
Response to rise in pH
Response to drop in pH
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Buffers protect against shifts in pH
H2CO3 HCO3- + H+
HCO3- + H+ H2CO3
Bicarbonate buffer system
H2CO3 H2O + CO2
Carbonic acid bicarbonate
Carbonic acidbicarbonate
Carbonic acid
Response to a rise in pH
Response to a drop in pH
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Range of Arterial pH Values
ACIDOSISpH = 1 to 7.40
NEUTRALpH = 7.41
ALKALOSISpH = 7.42 to 14.0
ACIDOSISlower than 7.0
ALKALOSIShigher than 7.8
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Normal Balance Between Acid and Base
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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 ?
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Any disease orcondition that affects the lungs,
kidneys, metabolism or breathing has the potential to cause acidosis or alkalosis.
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Causes of Acidosis
• Increased acid production within the body
• Consumption of substances that are metabolized to acids,
• Decreased acid excretion,
• Increased excretion of base.
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Causes of Alkalosis
• Electrolyte disturbances– prolonged vomiting or severe dehydration,– administration or consumption of base,
– Hyperventilation (increased CO2 production changes the pH)
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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
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Homeostasis of Acid-Base Balance
• Kidneys and Lungs
• Chemical Systems– Blood Buffers include:
• Hemoglobin• Bicarbonate• Phosphates• Plasma Proteins
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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
1 x 10-3 to 4 x 10 -5 6.0 to 7.4
Urine 3 x 10-2 to 1 x 10 -5 4.5 to 8.0
Gastric HCl 160 0.8
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More on Acid-Base Balance
• Text pp. 1008-1010– Chemical Buffering Systems
• Bicarbonate• Phosphate • Protein
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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
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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