1. Aim: How can we describe the various properties of water
Aim: How can we describe the various properties of water? Do Now: Why is water so important to us? Homework: Study for regents level exam Friday and review notes.

2. Water and the Fitness of the Environment
Chapter 2B
Water and the Fitness of the Environment

3. Importance of water Overview: The Molecule That Supports All of Life
Water is the biological medium here on Earth
All living organisms require water more than any other substance

4. Water Facts
Three-quarters of the Earth’s surface is submerged in water
The abundance of water is the main reason the Earth is habitable
Figure 3.1

5. Water Facts
The polarity of water molecules results in hydrogen bonding
The water molecule is a polar molecule

6. Properties of water
Six emergent properties of water contribute to Earth’s fitness for life
Cohesion/Adhesion
Surface tension
Temperature Moderation
High specific heat
Evaporative cooling
Universal solvent
Do brooks demo for surface tension.

7. Cohesion
Is the bonding of a high percentage of the molecules to neighboring water molecules
Is due to hydrogen bonding
Like molecules bonding to each other (water attracting other water molecules)

8. Water conducting cells
Cohesion
Helps pull water up through the microscopic vessels of plants (capillary action)
Water conducting cells
100 µm
Figure 3.3

9. Surface Tension
Is a measure of how hard it is to break the surface of a liquid
Is related to cohesion
Figure 3.4

10. Moderation of Temperature
Water moderates air temperature
By absorbing heat from air that is warmer and releasing the stored heat to air that is cooler

11. Water’s High Specific Heat
The specific heat of a substance
Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC

12. Specific Heat
Water has a high specific heat which allows it to minimize temperature fluctuations to within limits that permit life
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form

13. Evaporative Cooling Evaporation
Is the transformation of a substance from a liquid to a gas
Requires energy
Heat of vaporization
Is the quantity of heat a liquid must absorb for 1 gram of it to be converted from a liquid to a gas
100oC steam has MORE HEAT than 100oC boiling water (540 calories)

14. Evaporative Cooling Is due to water’s high heat of vaporization
Allows water to cool a surface
Sweating cools the body as heat energy from the body changes sweat into a gas

15. Insulation of Bodies of Water by Floating Ice
Solid water, or ice
Is less dense than liquid water
Floats in liquid water
Insulates water & organisms below ice layer

16. Insulation of Bodies of Water by Floating Ice
The hydrogen bonds in ice
Are more “ordered” than in liquid water, making ice less dense (crystal lattice)
Liquid water
Hydrogen bonds constantly break and re-form
Ice
Hydrogen bonds are stable
Hydrogen bond
Figure 3.5

17. Aim: How can we continue to describe the various properties of water
Aim: How can we continue to describe the various properties of water? Do Now: Is water polar or non-polar? Why is water termed the “universal solvent”? Homework: Study for regents level exam tomorrow and review notes. -Print-out notes for next week.

18. The Solvent of Life Water is a versatile solvent due to its polarity
Called the universal solvent because so many substances dissolve in water

19. Hydrophilic and Hydrophobic Substances
A hydrophobic substance:
Does not have an affinity for water
Nonpolar
Ex:lipids
A hydrophilic substance:
Has an affinity for water
Polar or ionic
Carbohydrates, salts

20. Acids and Bases
Dissociation of water molecules leads to acidic and basic conditions that affect living organisms
Organisms must maintain homeostasis in the pH of their internal and external environments

21. Effects of Changes in pH
Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions
Changes in the concentration of these ions Can have a great affect on pH in living organisms H
Hydronium
ion (H3O+)
Hydroxide
ion (OH–) + –
Figure on p. 53 of water dissociating

22. Acids and Bases
An acid
Is any substance that increases the hydrogen ion concentration of a solution
A base
Is any substance that reduces the hydrogen ion concentration of a solution (more OH- ions)

23. The pH Scale Scale goes from 0-14 with 7 neutral
The pH of a solution is determined by the relative concentration of hydrogen ions
Difference of 10X in hydrogen ion concentration between any two pH values
Acids have a higher number of H+ ions than a base
Acids produce H+ ion in solution
Bases produce OH- ions in solution
Have students practice pH math questions.

24. The pH scale and pH values of various aqueous solutions
Increasingly Acidic
[H+] > [OH–]
Increasingly Basic
[H+] < [OH–]
Neutral
[H+] = [OH–]
Oven cleaner 1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH Scale
Battery acid
Digestive (stomach)
juice, lemon juice
Vinegar, beer, wine,
cola
Tomato juice
Black coffee Rainwater
Urine
Pure water
Human blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Figure 3.8

25. Buffers The internal pH of most living cells must remain close to pH 7
Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution

26. The Threat of Acid Precipitation
Refers to rain, snow, or fog with a pH lower than pH 5.6
Is caused primarily by the mixing of different pollutants with water in the air

27. Can damage life in Earth’s ecosystems
Acid precipitation
Can damage life in Earth’s ecosystems 1 2 3 4 5 6 7 8 9 10 11 12 13 14
More acidic
Acid rain
Normal rain
More basic
Figure 3.9