1. Properties of Water

2. SWBAT Describe the unique properties of water
Adhesion -Unique density
Cohesion -high specific heat
Determine where water falls on the pH scale

3. Water: The Miracle Liquid
Although a person can live without food for more than a month, a person can only live without water for approximately one week.
Nearly 70% of your body is made of water
The average person in the United States uses 80 to 100 gallons of water each day. During medieval times a person used only 5 gallons per day.
97 % of earth’s water is in the oceans. Only 3 % of the earth’s water can be used as drinking water. 75 % of the world’s fresh water is frozen in the polar ice caps.

4. Structure of Water Remember: water looks like Mickey Mouse
These are 5 water molecules bonded together

5. O Structure cont. One end of water is partially positiveH O
One end of water is partially positive
The other end is partially negative
Oxygen is the negative end
Hydrogen is the positive end

6. Water is a POLAR molecule
Molecules with partial charges (+ end and a - end) are said to be polar.
These molecules are neutral overall because their charged ends cancel each other out
Partially charged ends attract negatively charged ends of other molecules
Everyday Items With Poles. . .

7. Why does POLARITY matter?
Negative particles are attracted to the positively charged hydrogen in a water molecule
Positive particles are attracted to the negatively charged oxygens in a water molecule. . .
Click here to see it!!!

8. Attraction leads to. . . . . .the ability to DISSOLVE in water!!!
Examples:
sugars dissolve due to polar attraction in water
Salts dissolve due to polar attraction in water
NONPOLAR molecules will not dissolve because they have no attractive charges within them

9. Why are the charges important?
The attraction between the hydrogen and the oxygen in adjacent molecules is called hydrogen bonding.
Many properties of water are due to hydrogen bonding.
                
Hydrogen Bonding between Water Molecules

10. Properties of Water Density
Water is a low density solid (Less dense as solid than as liquid)
Does ice float or sink in water?
Does a penny float or sink in water?
- Most dense > Least Dense
Liquid Water Ice Water Vapor

11. Why does it matter?
The low density of ice allows ice to float on liquid water in the winter.
If ice were MORE dense than liquid water, what would happen on the lakes?

12. Water Has a High Heat Capacity
The hydrogen bonds within and surrounding water molecules allows water to absorb a large amount of heat without changing temperature. The high heat capacity of water also allows water to cool down more slowly than other substances. . .

13. Why does it matter?
Thinking green: Water holds heat for long periods of time, allowing the bodies of water on Earth to help maintain a constant temperature
Thinking internally: The water in our bodies helps maintain an internal temperature balance (temperature homeostasis)

14. Water Molecules Stick to Each Other
Hydrogen bonds hold water molecules together tightly and strongly
Small drops of water are pulled together due to hydrogen bonds. Water molecules holding tight to each other is called cohesion

15. Why does it matter?
Cohesion helps water stay in its liquid state longer. If water molecules were not strongly attracted to each other, water would evaporate much more quickly.
THINK ABOUT IT: How would a faster evaporation rate affect life?

16. Water Molecules Stick to Other Polar Substances
Other polar substances are attracted to water. This is called adhesion.
Examples:
Water beads sticking to the side of a leaf
Water beads sticking to the side of a glass
Water beads sticking to the side of a graduated cylinder

17. Surface tension

18. Remember the meniscus???

19. Water and solutions Water is one of many solutions on the planet
SOLUTION: a mixture in which one or more substances are evenly distributed
Examples of solutions: bleach, milk, lemon juice, ammonia. . .

20. Every solution has a pH The pH scale ranges from 0 to 14.
Acids are substances on the pH scale that fall between 0 and 6.9
Bases are substances on the pH scale that fall between 7.1 and 14

21. Acids Strong acids have the LOWEST pH Weak acids have a pH close to 7
Examples of acids: lemon juice, cola, black coffee, stomach acid

22. Bases Strong bases have the HIGHEST pH Weak bases have the LOWEST pH
Examples: ammonia, bleach, Pepto-Bismol

23. Water has a NEUTRAL pH Water is the only substance with a pH of 7
Because it is considered neutral, water is neither and acid nor a base

24. pH and homeostasis
Different components of the body can only function within a certain pH range
Examples:
Human blood only functions properly at a pH around 7.4
In contrast, stomach acid is a strong acid that helps break down food. Anyone who has ever experienced an ulcer knows just how strong stomach acid is!