1. Notes
Section 2-2
Properties of Water
Lab

2. 1. Water – an unusual compound
Covers three fourths of our planet
Most abundant compound in living things
Liquid at room temp
Expands as it freezes
Lighter than most gases
Moderates temperatures by storing heat

4. 2. Water = H2O Covalent bonds hold the molecule together
Electrons are shared unequally
Oxygen takes most of the negative charge
Hydrogen atoms are left slightly positive

5. 3. Polarity Molecule has a positive side and a negative side
Due to unequal sharing of electrons
Weak bonds form
Called: hydrogen bonds

6. Polarity These weak hydrogen bonds are important
Causes water to attract other molecules
Water can hydrogen bond with up to 4 other water molecules

7. 4. Ionization
Any process by which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules (ions).
Causes molecules to separate into simpler molecules, atoms, or ions
Water attracts other ions and dissociates them
Conduction of nerve impulses
Contraction of muscles
Digestion of food

8. Ionization of Water

9. 5.Water has special properties due to hydrogen bonding
Cohesion – attraction between water molecules
Surface tension
Flow of water
Adhesion – attraction between water and other molecules
Water sticking to windshield
Capillary action – movement of water against the pull of gravity
Within plant stems

10. Here is a picture of water drops on pine needles, showing the effects of gravity, adhesion, and cohesion on water.
Gravity is shown by the water drops beading up at the bottom of the pine needles trying to fall to the center of the Earth .
The property of adhesion here is counteracting gravity, at least so far.
Adhesion causes the water to be sticky to the pine needle, thus preventing it from falling off the needle.
Cohesion is seen in the actual water drop—the water molecules stick to each other, forming a drop.

11. Cohesion Produces surface tension

12. Adhesion causes capillary action

13. Reading the Meniscus

14. 6. Mixture 2 or more elements or compounds mixed together
NOT chemically combined
e.g.
Soil
Air
Salt water

16. 7. Two types of mixtures 1. Solution: 1 or more dissolved chemicals
Solvent – chemical that others dissolve in
Solute – chemical that is dissolved
Water is the best solvent!!!
Aqueous solutions – solutions of water
Cl-
Water
Na+

17. Substances mixed in water, but not dissolved
2. Suspensions
Cytoplasm
Substances mixed in water, but not dissolved
Molecules are “suspended” in the water
e.g.
Blood contains proteins and cells
Cytoplasm contains organelles
Blood

18. 8. pH = “Power of Hydrogen Ion”
Indicates the concentration of H+ ions in solution
Range = 0 – 14
pH 7 = neutral concentration of H+ and OH- is equal

19. pH = “Power of Hydrogen Ion” continued
Each pH is 10x the
concentration of the previous
Example:
Change in pH from 10 to 12
concentration change equals…
10 x 10 or…
100

20. Sour taste Bitter taste
9. Acids vs. Bases
ACIDS BASES
pH < 7 pH > 7
Sour taste Bitter taste
Lots of H Lots of OH-

21. pH Scale 7 Acid Base 14 Acidic Neutral Basic [H+] pH 10-14 14 10-13 13
1 M NaOH
Ammonia
(household
cleaner)
Blood
Pure water
Milk
Vinegar
Lemon juice
Stomach acid
1 M HCl
Acidic Neutral Basic
Acid
Base 7 14
pH Scale
“S.P.L. Sorensen ( ) introduced the pH scale to measure the concentration of hydrogen ions in solution. The more hydrogen ions, the stronger the acid. The amount of hydrogen ions in solution can affect the color of certain dyes found in nature. These dyes can be used as indicators to test for acids and alkalis. An indicator such as litmus (obtained from lichen) is red in acid. If base is slowly added, the litmus will turn blue when the acid has been neutralized, at about 6-7 on the pH scale. Other indicators will change color at different pH’s. A combination of indicators is used to make a universal indicator.”
- Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 42

22. 10. Buffers Chemicals that neutralize small amounts of acids or bases
Controls pH which is important to maintaining homeostasis
Minimizes shifts in pH
Normal pH in humans is 6.5 – 7.5

24. Increasingly Basic Neutral Increasingly Acidic Sodium hydroxide
Oven cleaner
Bleach
Ammonia solution
Soap
Sea water
Human blood
Pure water
Normal rainfall
Acid rain
Tomato juice
Lemon juice
Stomach acid
Neutral
Increasingly Basic
Increasingly Acidic
Milk
Sodium hydroxide
Lye
Milk of Magnesia
Tums
Baking soda
Intestinal fluid
Urine
Spinach
Asprin
Cola
Battery acid

26. Importance of Water to Living Organisms
Most abundant compound in living matter
Universal solvent - dissolves many things
Needed for biological (metabolic) reactions
Transports materials
Regulates temperature
Needed to eliminate wastes
Protects and cushions vital organs
Lubricates joints and tissues
Reservoir of H+ and OH- ions