1. Chemistry of Water
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2. Outline Chemistry of Water Properties of Water pH Scale
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3. All organisms are approximately 2/3 water
Chemistry of Water
All organisms are approximately 2/3 water
¾ of the Earth is covered in water
Life existed for about 3 billion years in water before moving to land
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4. Structure of Water The water molecule is simple and stable
Covalent bonds
Octet rule satisfied
One oxygen atom bound to two hydrogen atoms by two single covalent bonds.
Polar Molecule - Has distinct ends, each with a partial charge.
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5. Hydrogen Bonds
In a water molecule, both oxygen and hydrogen atoms attract shared electrons in the covalent bonds (electronegativity).
Shared electrons more likely to be found near the O nucleus than near the H nuclei.
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6. Properties of Water Cohesion - Attraction to other water molecules.
Responsible for surface tension.
Reason why water is a liquid at Earth’s temperatures
Ex: As transpiration occurs from leaf surface, water is pulled up the xylem from the roots.
Adhesion - Attraction to other substance.
Capillary action also helps water move up the xylem of a plant
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7. Properties of Water
Polarity of water causes it to be attracted to other polar molecules.
More narrow tube, the greater the electrostatic forces between water and the wall of the tube
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8. Water Moderates Temperature
Heat Storage - Because of the large number of hydrogen bonds, a large input of thermal energy is necessary to break apart water molecules.
High Specific Heat -amount of energy needed to allow molecules to break free (break H-bonds) & increase in temperature
Amount of energy required to raise 1g of a substance by 1oC
Water = 1calorie/g/oC
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9. Water Moderates Temperature (continued)
High Heat of Vaporization (energy required to change liquid water to gas)
Water = 586 cal/g
Evaporation of water has a cooling effect on the surface from which it evaporates
Ex: sweating cools your body
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10. As water freezes, crystals form
Properties of Water
As water freezes, crystals form
Ice is less dense than liquid water due to the crystal lattice
Thus, ice floats.
Otherwise, inland bodies of water far from equator would stay solid year-round
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11. Ex: NaCl forms ions as it dissolves (quickly)
Properties of Water
Solvent - Water is an effective solvent because of its ability to form hydrogen bonds.
Water molecules gather around any substance bearing an electrical charge.
Ex: NaCl forms ions as it dissolves (quickly)
Ex: sugar has polar –OH groups (doesn’t dissolve as fast as salt)
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12. Raven - Johnson - Biology: 6th Ed
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13. Hydrophobic - Nonpolar molecules shrink from contact with water.
Properties of Water
Organization of Nonpolar Molecules - Water molecules act to exclude nonpolar molecules.
Hydrophobic - Nonpolar molecules shrink from contact with water.
(Water Hating)
Hydrophilic - Polar molecules readily form hydrogen bonds with water.
(Water Loving)
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14. Ionization - Spontaneous ion formation.
Water Ionizes
Ionization - Spontaneous ion formation.
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15. Water Ionizes
pH Scale - Measures negative logarithm of hydrogen ion concentration in the solution.
Acids - Substances that dissociate in water to increase concentration of H+ ions.
pH values below 7.
Bases - Substances that combine with H+ ions (and lower the concentration) when dissolved in water.
pH values above 7.
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16. Raven - Johnson - Biology: 6th Ed
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17. Water Ionizes Ex: Carbonic acid and bicarbonate (base)
Buffer - A substance that acts as a reservoir for hydrogen atoms.
Donates hydrogen atoms to solution when concentration falls, and removes them from the solution when concentration rises.
Minimize change in pH.
Ex: Carbonic acid and bicarbonate (base)
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18. Copyright © McGraw-Hill Companies Permission required for reproduction or display
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