Chapter 2: Water

1
Chapter 2 Water

• CHEM 4202
• Dr. Clower

2
Introduction

• What is the importance of water in biochemistry?
• Outline
• Physical properties
• Water as a solvent
• Reactivity of water

3
I. Physical Properties of Water
4
Results of H-bonding
5
Intermolecular Forces in Biochemistry
6
II. Water as a Solvent

• What substances are soluble? Insoluble?
• Solute-solvent attractions must be as strong or
  stronger than solute-solute or solvent-solvent
  attractions
• Solvation process

7
Hydrophobic Effect

• Tendency of water to minimize contact with
  hydrophobic compounds
• Thermodynamics unfavorable

8
Amphipathic

• Soap
• CH3(CH2)16CO2H KOH ? CH3(CH2)16CO2-K
• stearic acid potassium stearate
• Micelles and bilayers

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Micelles
10
Bilayers
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Colligative Properties

• Osmotic pressure (? icRT)
• Isotonic
• Hypertonic
• Hypotonic

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III. Reactivity of Water Acid-Base Chemistry

• A review
• H2O (l) H (aq) OH-(aq)
• K HOH-/H2O 1.8 x 10-16
• Kw KeqH2O HOH-
• At 25C, Kw 1 x 10-14
• In pure water, H OH-
• Therefore Kw H2
• And H 1 x 10-7

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Acids and Bases

• Brønsted-Lowry
• HA H2O A- H3O
• acid base conjugate
  conjugate
• base
  acid

14
Henderson-Hasselbalch Equation
15
Titration of acetic acid with OH-

• CH3CO2H NaOH CH3CO2-Na H-OH
• Titration curves for acetic acid, phosphate, and
  ammonia

16
Monoprotic vs. polyprotic acids

• CH3CO2H vs. H3PO4
• Titration of phosphoric acid

17
Chapter 2 Problems

• 2 13, 16
• Some are tricky
• Well go over in class next time