1. Essential Question: What makes water unique compared to other substances? Do Now: Explain why do you think water is important for life? HW: Water properties worksheet Binder check Wednesday

2. Properties of Water Cohesive nature of water
Ability to moderate temperature
Unusual phase changes
Versatile solvent

3. THE PROPERTIES OF WATER
1. Cohesion of Water
Water is a polar molecule, electrons are shared unequally
Cohesion is the ability of water molecules to attach to other water molecules
Attach by hydrogen bonds

4. In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
This makes the oxygen end of the molecule slightly negatively charged
The hydrogen end of the molecule is slightly positively charged
Water is therefore a polar molecule
(–)
(–) O H H
(+)
(+)
Figure 2.9

5. H+ atom is covalently bonded to the oxygen via a shared pair of electrons.
Oxygen is an "electronegative" or electron "loving" atom compared with hydrogen
"polar" molecule, meaning that there is an uneven distribution of electrons
This attraction forms weak bonds called hydrogen bonds

6. Surface Tension
The cohesion of water molecules at the surface of a body of water
Due to hydrogen bonding, water molecules can move from a plant’s roots to its leaves
Insects can walk on water due to surface tension created by cohesive water molecules

7. Adhesion Water can also be attracted to other materials.
Water can also be attracted to other materials.

8. Capillary Action
When one water molecule moves closer to the straw molecules the other water molecules also move up into the straw.
Water
Mercury

9. Water’s hydrogen bonds moderate temperature
Water has high specific heat
Specific heat = heat needed to raise temp. of 1g of substance by 1ºC
Boiling Point High .... water stays liquid longer
water can moderate Earth’s global temperature
able to absorb a great deal of heat energy without a large increase in temperature
As water cools, a slight drop in temperature releases a large amount of heat

10. Unusual Phase Change Gas Liquid Solid
Like no other common substance, water exists in nature in all three physical states:
as a liquid
as a gas
as a solid
Gas
Liquid
Solid

11. Hydrogen bonds are stable Hydrogen bonds constantly break and re-form
Density of Water
Ice is Less Dense than Liquid Water
Molecules in ice are farther apart than those in liquid water
Water is densest at 4°C.
Hydrogen bond
ICE
Hydrogen bonds are stable
LIQUID WATER
Hydrogen bonds constantly break and re-form
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

12. Water is a Versatile Solvent
Also known as the “Universal solvent”.
Polar substances are enveloped by hydration spheres.
“Like dissolves like!”

13. Solutions and Suspensions
Two types of mixtures can be made with water
Solutions
All the components of a solution are evenly distributed throughout the solution.
In a salt–water solution, table salt is the
solute—the substance that is dissolved.
Water is the solvent—the substance in which the solute dissolves

14. Solutions and Suspensions
Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out.
The movement of water molecules keeps the small particles suspended.
Suspension of flour in water

15. Acids, Bases, and pH Acids, Bases, and pH
A water molecule can react to form hydrogen and hydroxide ions.
H20  H+ + OH-
Water is neutral because the number of positive hydrogen ions (H+) produced is equal to the number of negative hydroxide ions (OH-) produced.

16. Acids, Bases, and pH The pH scale
Measurement system to indicate the concentration of H+ ions in solution.
The pH scale ranges from 0 to 14.
Solution
pH range
H+/OH- ratio
Acid
concentration of H+ ions greater than OH- ions
Neutral
7.0
concentration of H+ ions and OH- ions is equal.
Base
concentration of H+ ions less than OH- ions

17. Acids, Bases, and pH Acids
Any compound that forms H+ ions in solution. 
Contain higher concentrations of H+ ions than pure water
Strong acids tend to have pH values that range from 1 to 3.
The hydrochloric acid produced by the stomach to help digest food is a strong acid.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

18. Acids, Bases, and pH Bases
A base is a compound that removes H+ ions from a solution. 
Basic, or alkaline, solutions contain lower concentrations of H+ ions than pure water
Strong bases, such as lye, tend to have pH values ranging from 11 to 14.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

19. (Higher concentration of H+) (Lower concentration of H+)
pH scale
Acidic solution
Neutral solution
Basic solution
(Higher concentration of H+)
Increasingly ACIDIC
(Lower concentration of H+)
Increasingly BASIC
NEUTRAL
[H+] = [OH–]
Lemon juice; gastric juice
Grapefruit juice
Tomato juice
Urine
PURE WATER
Seawater
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
Human blood H+
OH–
The pH scale
Each pH unit represents a tenfold change in concentration of H+
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

20. Cabbage juice pH paper phenolphthalein pH Indicators -turns pink in
presence of base

21. Acids, Bases, and pH Buffers
The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5.
If the pH is lower or higher, it will affect the chemical reactions that take place within the cells.
enzymes denature & reactions stop (That’s a bad thing!)

22. Connection: Acid precipitation threatens the environment
Some ecosystems are threatened by acid precipitation
Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

23. Properties of Water
A molecule in which the charges are unevenly distributed is called a
polar molecule.
cohesive molecule.
hydrogen molecule.
covalent molecule.

24. Properties of Water 2
Hydrogen bonds between water molecules result from
adhesion between water molecules.
magnetic attractions between water molecules.
uneven electron distribution in each water molecule.
ionic bonds in the water molecule.

25. Acids, Bases, and pH 1 A dissolved substance is called a solvent.
solution.
solute.
suspension.

26. Acids, Bases, and pH 2
A compound that removes ions from a solution is called a(an)
base.
buffer.
acid.
salt.

27. Acids, Bases, and pH 3
On a pH scale, a value of 2 means that the solution has
equal concentrations of H+ and OH- ions.
the same concentration of H+ ions as pure water.
higher concentration of H+ than in pure water.
lower concentration of H+ than in pure water.

28. Acids, Bases, and pH 4
Tomato juice has a pH of 4, while soap has a pH of 10. How much more acidic is the juice?
6 times more acidic
1,000,000 times more acidic
60 times more acidic
1,000 times more acidic