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 propertiesWater 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

01

2

3

4

5

6

7

8

9

3Amount 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