1. Properties of H20
Why water is special?

2.
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3. Polarity
Polarity describes the distribution of electrons in a molecule
Polar molecules have an uneven distribution of electrons.
Example: Water
8 protons in the nucleus of Oxygen that attract electrons of Hydrogen very strongly.
Water has a partial negative charge on one end and partial positive charge on the other end. + -

4. Hydrogen Bonding
Weak attraction between a hydrogen atom and another atom.
Polar molecules, like water, attract each other.
Hydrogen bonds contribute to the unique characteristics of water.
Examples of unique properties of water:
Expands slightly upon freezing, making ice less dense than liquid water.
Water is a universal solvent and is able to dissolve many other substances, a property that is essential in living cells.
Cohesion
Adhesion
Heat Capacity

5. Cohesion
Cohesion is the attractiveness of molecules of the same substance to one another.
Water has a high cohesion because it can bond to 4 other H2O molecules at once, which explains why water beads on surfaces.
The water molecules are so attracted to themselves that they do not spread apart readily.
This attraction is due to hydrogen bonds between H+ of one atom & O- of another.
Also called surface tension
YouTube:
Surface Tension
YouTube:
Jesus Lizard
Hydrogen
Bonding

6. Adhesion
Adhesion is the attractiveness of molecules between different substances
Water also has high adhesiveness.
Explains why water attempts to creep up the sides of a graduated cylinder and form a meniscus.
Also called capillary action—which is one of the forces that draws water out of the roots of a plant and up into its stems and leaves.

7. High Specific Heat
Specific Heat: Amount of heat needed to raise or lower 1g of a substance 1° C.
Due to the high number of hydrogen bonds between water molecules it takes a large amount o f heat energy to cause the molecules to speed up.
Water has to absorb Joules of heat for the temperature of one gram of water to increase 1 degree celsius (°C).
Water resists temperature change, both for heating and cooling.
This allows large bodies of water to absorb large amounts of heat with only small changes in temperature.
Living organisms are also protected from drastic changes into temperature.

8. High Heat of Vaporization
Amount of energy to convert 1g or a substance from a liquid to a gas
In order for water to evaporate, hydrogen bonds must be broken.
As water evaporates, it removes a lot of heat with it.
Water's heat of vaporization is 540 cal/g.
Water vapor forms a kind of global ‘‘blanket”
which helps to keep the Earth warm.
Heat radiated from the sun warmed surface
of the earth is absorbed and held by the vapor. 1

9. Water is Less Dense as a Solid
Ice is less dense as a solid than as a liquid (ice floats)
Liquid water has hydrogen bonds that are constantly being broken and reformed.
Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances.
Which is ice and which is water?
Figure 1
Figure 2 1

10. Water & Homeostasis
Ability to maintain a steady state despite changing conditions
Water is important to this process because:
a. Makes a good insulator
b. Resists temperature change
c. Universal solvent
d. Coolant
e. Ice protects against temperature extremes (insulates frozen lakes) 4

11. Solutions, Mixtures and Suspensions
Mixture- a substance that is made of two or more elements physically mixed together
Example: Mixing Skittles and M&Ms together
Solution - a type of mixture where one substance is dissolved in another.
Solute- the substance that is dissolved
Solvent- the substance that does the dissolving
Suspension- Substances that don’t dissolve but separate into tiny pieces.
Water keeps the pieces suspended so they don’t settle out.

12. Water as a solvent
Water is often referred to as the “Universal Solvent” because of it’s ability to dissolve such a wide variety of substances.
GO WATER!!!

13. The pH Scale (Acidic, Basic, Neutral)
pH is a measure of the concentration of of H+ ions
(pH=power of Hydrogen)
Describes how acidic or basic (alkaline) something is
pH 0-6 = acid – substance forms H+ ions in water
Ex: Lemon juice (pH=2)
pH 7 = neutral
Ex. Pure water and blood
pH 8-14 = base (alkaline) – substance forms OH+ ions in water
Ex. Ammonia (pH= 12)

14. Identifying the pH of Substances
Indicator- a substance, as litmus, that indicates the presence or concentration of a certain constituent.
Red Litmus Paper turns BLUE in the presence of a Base.
Blue Litmus Paper turns RED in the presence of an Acid.
pH paper detects H+ ions and identifies the specific pH of a substance.

15. Buffers Buffers: Solutions that prevent sudden changes in pH.
Neutralization reaction:
HCl + NaOH → HOH + NaCl (HOH is the same as H2O)
Another way to say it:
HCl + NaOH → water + salt
Buffers help living organisms maintain internal stability. This is called ______________________.