1. What makes water so special?

2. KEY CONCEPT Water’s unique properties allow life to exist on Earth.

3. Polar Molecule and Hydrogen bonds
Water is a polar molecule.
Polar molecules have slightly charged regions. O H _ +
Nonpolar molecules do not have charged regions.
Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.
Because an oxygen nucleus has 8 protons and it pulls harder on the shared electrons than does Hydrogen with only 1 proton. Oxygen becomes slightly negative. Nonpolar share electrons more equally

4. Properties of water
Life depends on hydrogen bonds
Hydrogen bonds are responsible for three important properties of water.
high specific heat
cohesion
adhesion
Weak bond, but strong in numbers

5. Attraction between molecules of the same substance
Cohesion
Attraction between molecules of the same substance
Caused by hydrogen bonding between water molecules

6. Water molecules on the surface stick together
Surface Tension
Water molecules on the surface stick together
Attraction is fairly strong
Forms a “Film” at the surface

7. Attraction between molecules of different substances
Adhesion
Attraction between molecules of different substances
Water sticking to web
Paint to walls
Results in Capillary action which allows water to climb structures

8. Amount of heat needed to raise or lower 1g of a substance 1° C.
High Specific Heat
Amount of heat needed to raise or lower 1g of a substance 1° C.
Water resists temperature change, both for heating and cooling.
Would you rather walk on sand or in water on a beach on a hot summer day? 1

9. Water is Less Dense as a Solid Which is ice and which is water?1

10. Solutions and Suspensions
A solution is formed when one substance dissolves in another.
Many compounds dissolve in water
A solution is a homogeneous mixture.
Solvents dissolve other substances.
Solutes dissolve in a solvent.
solution

11. Ex blood
Liquid part plasma 95% water = Solvent
Solutes = sugars, proteins etc.

12. “Like dissolves like.”
Polar solvents dissolve polar solutes.
Dissolve because attraction between water and solute is greater than attraction between solute
Ionic compounds (NaCl) dissolve because ions are attracted to water and water surrounds and rips apart molecule
Nonpolar solvents dissolve nonpolar solutes.
Polar substances and nonpolar substances generally remain separate.
Ex “Oil and water don’t mix”

13. Suspensions
Substances that don’t dissolve but separate into tiny pieces.

14. H2O  H+ + OH- Acids, Bases and pH
One water molecule is made of two ions, (H+) and Hydroxide Ion (OH-)
Hydrogen Ion Hydroxide Ion
Acid Base
H2O  H+ + OH-

15. The pH Scale
Indicates the percent of H+ ions
Ranges from 0 – 14
pH of 7 is neutral
Each pH unit represents a factor of 10X change in concentration
pH 3 is 10 x 10 x 10 (1000x) stronger than a pH of 6

16. An acid releases a hydrogen ion when it dissolves in water.
Acids, Bases and pH
An acid releases a hydrogen ion when it dissolves in water.
high H+ concentration
pH less than 7
more acidic
stomach acid pH between 1 and 3

17. A base removes hydrogen ions from a solution.
low H+ concentration
pH greater than 7
bile pH between 8 and 9
more basic

18. A neutral solution has a pH of 7.
Buffers are weak acids and bases produced by the body to keep pH neutral
Maintain homeostasis
Can you think of a buffer to neutralize acid indigestion?
pure water pH 7