1. Properties of Water

2. Water is a Polar Molecule -has oppositely charged ends
Water consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds.
Oxygen has unpaired & paired electrons which gives it a slightly negative charge while Hydrogen has no unpaired electrons and shares all others with Oxygen
Leaves molecule with positively and negative charged ends
Water is a Polar Molecule -has oppositely charged ends

3. slightly positive charge
hydrogen bond between (+) and (-) areas of different water molecules
slightly negative charge

4. Water’s Properties
Cohesion
Adhesion
Capillarity
High Specific Heat
High Heat of Vaporization
Solid water (ice) is less dense than liquid
Solvent
Transparent

5. Cohesion refers to attraction to other water molecules.
responsible for surface tension
a measure of the force necessary to stretch or break the surface of a liquid

6. Adhesion refers to attraction to other substances.
Water is adhesive to any substance with which it can form hydrogen bonds.

7. water evaporates from leaves = transpiration
Capillary action
All thanks to hydrogen bonding!
adhesion, cohesion and capillary action
water taken up by roots

8. Trees have specialized structures to transport water: xylem and phloem “plumbing”
Water molecules are “dragged” from the roots to the top of the tree by capillary action and cohesion: hydrogen bonds help water molecules to each other

9. High Specific Heat
High specific heat
Amount of heat that must be absorbed or expended to change the temperature of 1g of a substance 1o C.

10. Impact of water’s high specific heat
The Earth is over 75% water!
A large body of water can absorb a large amount of heat from the sun in daytime and during the summer, while warming only a few degrees.
At night and during the winter, the warm water will warm cooler air.
Ocean temperatures and coastal land areas have more stable temperatures than inland areas.
The water that dominates the composition of biological organisms moderates changes in temperature better than if composed of a liquid with a lower specific heat.

11. High heat of vaporization
Amount of energy required to change 1g of liquid water into a gas (586 calories).
large number of hydrogen bonds broken when heat energy is applied

12. As a liquid evaporates, the surface of the liquid that remains behind cools - Evaporative cooling.
Evaporative cooling moderates temperature in lakes and ponds and prevents terrestrial organisms from overheating.
Evaporation of water from the leaves of plants or the skin of animals removes excess heat.

13. “Universal” Solvent
A liquid that is a completely homogeneous mixture of two or more substances is called a solution.
A sugar cube in a glass of water will eventually dissolve to form a uniform mixture of sugar and water.
water is the solvent and
sugar the solute.
In an aqueous solution, water is the solvent.
Water is not really a universal solvent, but it is very versatile because of the polarity of water molecules.

14. Water is an effective solvent as it can form hydrogen bonds.
Water clings to polar molecules causing them to be soluble in water.
Hydrophilic - attracted to water
Water tends to exclude nonpolar molecules.
Hydrophobic - repelled by water

15. Water transports molecules dissolved in it
Blood, a water-based solution, transports molecules of nutrients and wastes organisms
Nutrients dissolved in water get transported through plants
Unicellular organisms that live in water absorb needed dissolved substances

16. Solid water (ice) is less dense than liquid
Ice is less dense than water: the molecules are spread out to their maximum distance
Density = mass/volume
same mass but a larger volume

17. Oceans and lakes don’t freeze solid because ice floats
water expands as it solidifies
Water reaches maximum density at 4-degrees C
Water freezes from the top down

18. Water is Transparent
The fact that water is clear allows light to pass through it
Aquatic plants can receive sunlight
Light can pass through the eyeball to receptor cells in the back

19. pH Water ionizes into H+ and OH- H2O H+ and OH-
pH scale expresses hydrogen ion (H+) concentration in a solution.
logarithmic scale ranging from 0-14
neutral = 7
Below 7 = acid
Above 7 = base
Water at 25oC contains 1/10,000,000 mole of H+ ions = moles/liter
pH = -log [H+]

21. Acids
Acids dissociate in water to increase the concentration of H+.
Have many H+ ions
Sour taste
HCl is hydrochloric acid or stomach acid

22. Bases
Bases combine with H+ ions when dissolved in water, thus decreasing H+ concentration.
Have many OH- (hydroxide) ions
Bitter taste
NaOH = sodium hydroxide or baking soda