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

Acids and Bases

Chapter 2 pp. 39-41

Also pp. 1008-1010

3

Oxygen (O)

(8p+,8n0,8e-)

2 electrons + 6 electrons

4

Special Properties of Water

5

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

6

The pH Scale

Acid and Base

7

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.

8

Hydrogen ionHydrogen

H H+

9

Fig. 2.13 in text

As the Hydrogen ionconcentration increases, the Hydroxyl ion concentration decreases

Neutralization

• Mixing acids and bases

• Displacement reaction to form a water and a salt

• HCL + NaOH NaCl + H20

11

DISSOCIATION OF NaCl

12

Hydrochloric Acid (Strong Acid)

Carbonic acid (Weak Acid)

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

15

EQUILIBRIUM

A + B AB

16

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

17

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

18

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

19

20

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

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 orcondition 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

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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

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