Date post: | 19-Dec-2015 |
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Water
I. Water and hydrogen bondingII. Properties of waterIII. Acids and bases
A bit about water . . . .
• Polar covalent bond : bond in which electrons are shared unequally.
Water and hydrogen bonding
Hydrogen bonds
• Cohesion
• Temperature stabilizing capacity
• Insulation of bodies of water by ice
• Solvent properties
Properties of water
Due to H-bonding, water is highly cohesive. Cohesiveness accounts for high surface tension
Cohesiveness
Water-conducting cells
100 µm
Cohesiveness
Water and Temperature
Specific heat - amount of energy a substance must absorb per gram to increase temp 1 degree C
Temperature stabilizing capacity
Specific heat - amount of energy a substance must absorb per gram to increase temp 1 degree C
Temperature stabilizing capacity
specific heat of water is 1 cal/gram
Specific heat of water is higher than most other liquids because of extensive H-bonding
Water and temperature
Effect of a large body of water on temperature
High specific heat buffers against temperature increases
Important in context of cell biology because cells release large amounts of energy during metabolic reactions.
Release of heat would pose overheating problem were it not for high specific heat of water
High specific heat of water
Evaporative Cooling
Ice Floats
Solvent of Life
Solvent properties
Water is an excellent solvent for biological purposes because of its ability to dissolve great variety of solutes.
Hydrophilic
Hydrophobic
• Hydrophilic: polar molecules that dissolve readily in water; sugars, organic acids, some amino acids.
• Hydrophobic: non-polar molecules that are not very soluble in water. lipids, some proteins
Solvent properties
Water is a polar solvent
Water Disassociates
H+ OH -
• pH scale expresses hydrogen ion (H+) concentration in a solution.– logarithmic scale ranging from 0-14
• neutral = 7
Acids and bases
pH
• Acids dissociate in water to increase the concentration of H+.– pH values lower than 7
• Bases combine with H+ ions when dissolved in water, thus decreasing H+ concentration.– pH values above 7
more OH-
pH scalemore H+
10
0
1
2
3
4
5
6
7
8
9
3
Amount of base added
Bufferingrange
4 52
pH
•Buffers act as a reservoir for hydrogen ions, donating or removing them from solution as necessary.
Acid Precipitation
Coal
Damage from Acid Rain