1. Test Review Valid Experiments & their Parts Water & Its Properties

2. Designing a valid experiment

3. Valid Experiments Given an experiment be able to: Identify the parts:
Independent variable (levels being tested)
Dependent variable (effect being measured)
Control group
(level getting no treatment or normal treatment)
Constants
Tell whether or not the experiment was valid

4. Identify the Parts of an Experiment
Example:
Cody and Blake design an experiment see if reading a Social Studies textbook every night has any effect on Social Studies test grades. They have one group of students solemnly swear to read their textbook for 30 min., another group 60min., and a third group read for 90 minutes. All three groups are assigned the same chapter, have the same number of boys and girls, and are all the same grade. After 8 school nights, all three groups take the same test, and all the scores are recorded. The experiment is later repeated two more times that quarter.
Is the experiment valid (well designed)?

5. Water’s Structure & Properties

6. Water’s Unique Structure
Water is a molecule composed of
1 oxygen atom and
2 hydrogen atoms
Formula of water: H2O
Structure of the water molecule:
Water is a “polar” molecule.
The oxygen end (pole) of water has a partially negative charge.
The hydrogen end (pole) of water has a partially positive charge.

7. Cohesion: Water molecules are attracted to other water molecules

8. Surface Tension
Cohesive forces hold water molecules together tightly at the surface

9. Drops of Water on a Penny: Cohesion & Surface Tension

10. Adhesion
Water molecules stick to “other” things… molecules other than water.

12. Capillary Action Cohesion and adhesion (both) working together
Allows water to move upward against gravity in plants and trees

13. Heat of Vaporization
Vaporization and evaporation are when water changes from liquid water to gas (vapor).
In order for water to evaporate, it must absorb a lot of heat.
Oceans and lakes absorb a lot of heat energy for water to evaporate.
When we sweat, the water in the sweat removes a lot of heat from our body as it evaporates.

14. Why do snowflakes have 6 sides?
Water molecules arrange themselves, as temperature drops to freezing, into a hexagonal shape. The opposite charges of the polar ends of the molecule attract to the water molecule next to it.

15. Density Ice is less dense than liquid water

16. Density Density = mass/volume
Be able to calculate density when given the mass and volume of a substance.

17. Water’s Properties are Caused by Water’s Polar Structure
It takes a lot of energy to make water change from liquid to gas (vapor). Why sweating cools us.
When water freezes into a solid, it actually becomes LESS dense because the water molecules form a hexagon shape.
H2O sticks to other H2O
Water molecules at the surface are more tightly held together than the molecules under the surface.
H2O sticks to molecules other than water.
When cohesion and adhesion work together to draw water upward, against gravity, in trees and plants.
Cohesion
Adhesion
Capillary Action
Surface Tension
Density
High heat of vaporization