2. Water Chemistry &
Properties of Water

3. Warning:
This powerpoint is from a high school teacher. This is the language and format that a lot of your teachers will use.
GOAL: Learn to take notes by writing down THE MOST IMPORTANT information in the least amount of words.

4. Biology Benchmarks
SC.912.L Discuss the properties of water that contribute to Earth’s suitability as an environment for life: cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent. Moderate
SC.912.N Define a problem based on a specific body of knowledge and pose answers, explanations, or descriptions of events. High

5. Engage:
Demonstration Polarity of Water: Water Bending

6. Water Drops on a Penny Investigation
Explore:
Water Drops on a Penny Investigation
See Here:

7. < 0o C - ice; 0o C - 100o C – liquid; > 100o C - steam

8. 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

9. Water molecules form Hydrogen bonds
slightly positive charge
hydrogen bond between (+) and (-) areas of different water molecules
slightly negative charge

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

13. Cohesion Water clings to polar molecules through hydrogen bonding
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

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

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

16. 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

18. 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.

19. Impact of water’s high specific heat ranges from the level of the whole environment of Earth to that of individual organisms.
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.
Therefore, 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.
The Earth is over 75% water!

20. Quick Check:
How would the global climate be different if the majority of the Earth was land?
JUSTIFY!

21. 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

22. 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.

23. “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.
The dissolving agent is the solvent and the substance that is dissolved is the solute.
In our example, 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.

24. 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

25. 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

26. Why Does Ice Float?
Video Clip:

27. 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

28. Oceans and lakes don’t freeze solid because ice floats
water expands as it solidifies
water reaches maximum density at degrees C
water freezes from the top down
organisms can still live in the water underneath the ice during winter

29. 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

30. pH

31. pH = -log [H+] 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+]

32. pH

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

34. 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

35. Buffers
Buffers
act as a reservoir for hydrogen ions, donating or removing them from solution as necessary
Offer protection from extreme pH levels
Produced naturally by organisms:
Organisms can’t tolerate much pH change
Cells function best within a narrow pH range

36. Reflect:
How does the high school content differ from the middle school content?