1. Properties of Water

2. Water statistics Covers 75% of Earth’s surface
(why understanding it is important!)
Covers 75% of Earth’s surface
97% oceans
3% freshwater
2% (of Total) in ice caps and glaciers
1% in lakes, underground, or in atmosphere (usable by humans)
Makes up 70% of the human body
92% of blood plasma
80% of muscle tissues
60% of red blood cells

3. Physical properties Water:
Is clear, colorless, odorless, and tasteless
* Colors, tastes and odors are caused by substances dissolved in the water.
Boils at 100°C
Freezes at 0°C
Density = 1.0 g/mL (at 4°C)

4. Properties of Water Cohesion Adhesion High Specific Heat
High Heat of Vaporization
Less Dense as a Solid

5. molecule with uneven distribution of charge
Biochemistry
Water
Polar molecule
molecule with uneven distribution of charge
water is polar, O atom pulls electrons from H atoms causing an unequal sharing of electrons

6. Each water molecule can form hydrogen bonds with up to four neighbors.
The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.
Each water molecule can form hydrogen bonds with up to four neighbors.
Fig. 3.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

7. HYDROGEN BONDS
The hydrogen bonds joining water molecules are weak, about 1/20th as strong as covalent bonds.
They form, break, and reform with great frequency
Extraordinary Properties that are a result of hydrogen bonds.
Cohesive behavior
Resists changes in temperature
High heat of vaporization
Expands when it freezes
Versatile solvent

8. Properties of Water
Cohesion is the tendency of molecules of the same kind to stick to one another.
Water has stronger cohesion than most liquids
water is transported up inside trees and other vascular plants inside tiny tubes call "xylem vessels". As water transpires off the leaves the cohesion pulls more water up through the vessels.

9. Cohesion pulls molecules at the surface tightly together, forming a film-like boundary, creating water’s surface tension.

10.  Surface Tension
The collective strength of hydrogen bonds forms a film on the surface of water
Ex: floating a paper clip, “water striders”, water beading on waxed car
Air
Water

11. Adhesion-Attraction between unlike molecules
Ex: water moving up the roots of a tree this is called capillary action

12. Water molecules attracted to sides of container
Biochemistry
Adhesion
Water molecules attracted to sides of container

13. Capillary Action
Capillary action = Water is able to “climb” objects against the forces of gravity
Think of the (+) and (-) ends of a water molecule acting like suction cups, and a water molecule is using them to climb up a glass building

14. Water is Less Dense as a Solid
Density of ice (at 0°C) is g/mL, so ice floats in water.
Most liquids become more dense as you cool them. However, when water freezes, a large expansion occurs.
* Where have you see H2O in repeating hexagonal patterns before?
Water “organizing” with H bonds as it freezes.
Forms hexagon shapes.

15. So ice is able to float (just barely)

16. Universal Solvent
Solvent – a substance that dissolves another substance
What dissolves in water?
Salt, Sugar, Carbon Dioxide, Oxygen, MANY more!
For an object to dissolve in water it must also be a polar molecule!
This is why oil and water do not mix, oil is NON-polar

17. Water resists temperature change, both for heating and cooling.
High Specific Heat
Water resists temperature change, both for heating and cooling.
Water can absorb or release large amounts of heat energy with little change in actual temperature.
At the beach, why is the sand hotter than water at noon but cooler than water at midnight? 1

18. Water has a High Heat of Vaporization
Evaporative Cooling - the cooling of a surface occurs when the liquid evaporates
This is responsible for:
Moderating earth’s climate
Preventing organisms from overheating

19. Discussion Questions
Which property of water causes the cracks in the pavement in cold climates?
Why does a meniscus form on the surface of the water in a graduated cylinder?
What property of water best describes the ability of water to clean our clothes?

20. Acids, Bases, and pH

21. A scale of 1-14 is used to describe pH
pH scale
– Measurement system that indicates the concentration of hydrogen (H+) ions in solution
A scale of 1-14 is used to describe pH

22. Acids
Acids have a pH range of 1-6
Produce lots of H+ ions

23. Bases Bases have a pH range of 8 to 14
Contain lots of OH-ions and fewer H+ ions

25. Acids and Bases
Acid – any substance that forms hydrogen ions (H+) in water
Acidic solutions contain higher concentrations of H+ ions and pH lower than 7.
Base – any substance that forms hydroxide ions (OH-) in water
Basic, or alkaline, solutions contain lower concentrations of H+ ions and pH higher than 7.

26. Buffers
A substance that prevents sharp, sudden changes in pH (neutralization).
Produced naturally by the body to maintain homeostasis
Weak Acid
Weak Base