Water, Water Everywhere

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Water, Water Everywhere
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Water is a Polar Molecule Figure 2.1
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Polarity of Small Molecules Figure 2.2
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Hydrogen Bonding Between Two Water
Molecules Figure 2.3
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Water Can Form Up To Four Hydrogen Bonds Figure
2.4
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Water Molecules Form a Hexagonal Lattice in
Ice Figure 2.5
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Sodium Chloride (NaCl) crystal Figure 2.6
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Ionic and PolarSubstances Dissolvein
Water Example Dissolution ofSodium Chloride
in water Figure 2.6
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Glucose, a sugar, contains polar groups, and is
soluble in water
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Nonpolar substances are relatively insoluble in
water
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Noncovalent interactions in biomolecules

• Charge-Charge Interactions
• Hydrogen Bonds
• Van der Waals Forces
• Hydrophobic Interactions

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Hydrogen bonding isa common noncovalentinteracti
on between biomolecules Figure 2.10
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Hydrogen bonding between bases in DNA Figure 2.11
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Van der Waals forces are weak noncovalent
forces between atoms Figure 2.12
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Amphipathic molecules,such as detergents,have
both a polar anda nonpolar end.
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Detergents can form monolayers at the air-water
interface Figure 2.9
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Detergents can form micelles in aqueous
solution Figure 2.9
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Water can act as a nucleophile in biological
reactions Figure 2.14
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Water often is excluded from the active sites of
enzymes,the biological catalysts. Figure 2.15
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Ionization of Water
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Water has a slight tendency to ionize Page 35
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Strong acids completely dissociate in
water. Example Hydrochloric acid (HCl)
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Weak acids dissociate in water with a
characteristicacid dissociation constant
(Ka). Example Acetic acid, present in vinegar
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Relationship between pH and pKa
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Titration of acetic acid with aqueous base Figure
2.17
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Titration of phosphoric acid,a polyproticacid,
withaqueous base Figure 2.19
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1 2 3 4 5 6 7 8 9 10
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• Write the equilibrium reaction for the ionization
  of the weak acid.
• What is the chemical structure of the conjugate
  base?
• What is the pH of a solution containing equal
  amounts of theweak acid and the conjugate base?
• What is the pH of a solution containing 10 times
  more weak acidthan conjugate base?
• What is the ratio of conjugate base to weak acid
  at pH 7?

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• Write the equilibrium reaction for the ionization
  of the weak acid.
• What is the chemical structure of the conjugate
  base?

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• Write the equilibrium reaction for the ionization
  of the weak acid.
• What is the chemical structure of the conjugate
  base?
• What is the pH of a solution containing equal
  amounts of theweak acid and the conjugate base?

CH3COO-
4.8
CH3COOH
1
4.8
0
4.8
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• Write the equilibrium reaction for the ionization
  of the weak acid.
• What is the chemical structure of the conjugate
  base?
• What is the pH of a solution containing equal
  amounts of theweak acid and the conjugate base?

CH3COO-
4.8
CH3COOH
1
4.8
0
4.8
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4. What is the pH of a solution containing 10
times more weak acidthan conjugate base?
CH3COO-
4.8
CH3COOH
0.1
4.8
4.8
(-1)
3.8
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5. What is the ratio of conjugate base to weak
acid at pH 7?
CH3COO-
7
4.8
CH3COOH
CH3COO-
2.2
CH3COOH
CH3COO-
102.2
CH3COOH
CH3COO-
158
CH3COOH
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In the laboratoryBuffer PreparationPage 42
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Titration of acetic acid with aqueous base Figure
2.17
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Titration of acetic acid with aqueous base Figure
2.17
Buffering Region 1 pH unit from pKa
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Buffer Preparation
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Maintenance of Blood pHin HumansCO2
Bicarbonate Buffer System
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Carbon dioxide carbonic acid bicarbonate
buffer systemmaintains blood pH at 7.4 Figure
2.20
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Regulation ofblood pHin mammals Figure 2.21
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Why is the CO2 bicarbonate buffer system used
in the human body?

• The raw materials (CO2 and H2O) for the
  production of carbonic acid (H2CO3) are readily
  available.
• The lungs and kidneys can easily adjust to ratio
  alterations between carbonic acid (H2CO3) and
  the conjugate base bicarbonate (HCO3-).

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Role of the lungs and kidneys inregulation of
physiological pH
Lungs Control the supply of H2CO3 in the blood by
controlling theamount of CO2 exhaled. When the
blood level of HCO3- decreases, the breathing
rate isincreased, increasing amount of CO2
expelled, decreasing H2CO3. If H2CO3 (CO2)
increases it is called respiratory acidosis. If
H2CO3 (CO2) decreases it is called respiratory
alkalosis. Kidneys Control the concentration of
HCO3-. If HCO3- is too high it is called
metabolic alkalosis. If HCO3- is too low, it is
called metabolic alkalosis.
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Blood Concentrations
Ratio of HCO3- H2CO3 20 1 ? This results in
pH 7.4 HCO3- 24 - 27 mEq/L (mM) H2CO3 1.20
- 1.35 mEq/L (mM) Clinicians often monitor blood
pH, HCO3- and CO2 concentrations. Non-graded
Homework Use Henderson-Hasselbalch equation to
convince yourselfthis makes sense. Problem 11
at the end of the chapter.