1. Chapter 3
Water and Life

2. WATER: All living organisms must have water to survive.
Most cells are surrounded by water, and cells themselves are about 70–95% water.
The abundance of water is the main reason the Earth is habitable
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3. The water molecule is a polar molecule:
Two hydrogen atoms form a polar covalent bond with the oxygen atom.
Hydrogen atoms will have a partial positive charge while the oxygen atom will have a partial negative charge. This allows an attraction between molecules…..
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4. Polarity allows water molecules to form hydrogen bonds with four other molecules. 
Hydrogen
bond  +
Polar covalent
bonds    +    +    +
Figure 3.2 Hydrogen bonds between water molecules. 4

5. Water has a variety of unusual properties because of the attraction between the polar water molecules.
Figure 3.1 How does the habitat of a polar bear depend on the chemistry of water? 5

6. Water’s properties facilitate an environment conducive to life:
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing/ Density
Versatility as a solvent
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7. Cohesion of Water Molecules
At any instant, a large percentage of all water molecules are bonded to their neighbors, creating a high level of structure.
Collectively, hydrogen bonds hold water together, a phenomenon called cohesion.
Cohesion is important. Examples:
Helps move water from roots to leaves in plants
Causes surface tension
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8. Adhesion, clinging of one substance to another causes water to adhere to the walls of other things.
Ex: xylem in plants and glass containers.

9. Two types of water-conducting cells
Figure 3.3
Adhesion
Two types of
water-conducting
cells
Cohesion
Direction
of water
movement
Figure 3.3 Water transport in plants.
300 m 9

10. Surface tension is a measure of the force necessary to break the surface of a liquid.
Water has high surface tension because surface molecules have uneven attractive forces around them.
Molecules below the surface attract those on the surface. No such attraction occurs from the top.
Surface tension resist stretching or breaking the surface. This allows some animals to stand, walk or run without breaking the surface.

11. Figure 3.4
Figure 3.4 Walking on water. 11

12. Moderation of Temperature by Water
Water can absorb or release a large amount of heat with only a slight change in its own temperature.
Heat is a measure of the total kinetic energy of a substance due to the motion of molecules.
Temperature measures the average kinetic energy of molecules.
We use the Celsius scale to measure temp.(°C)
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13. A calorie (cal) is a measurement of the amount of heat required to raise the temperature of 1 g of water by 1°C.
The “calories” on food packages are actually kilocalories (kcal), where 1 kcal = 1,000 cal
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14. Water Has High Specific Heat
Specific heat is the amount of heat required for
1 g of a substance to change temperature by 1ºC
The specific heat of water is 1 cal per gram per ºC
Water’s high specific heat is caused by its intermolecular attraction due to hydrogen bonding.
Water resists changes in temperature because of its high specific heat, which is beneficial to life.
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15. Los Angeles (Airport) 75°
Figure 3.5
San Bernardino
100°
Burbank
90°
Santa Barbara 73°
Riverside 96°
Los Angeles
(Airport) 75°
Santa Ana
84°
Palm Springs
106°
70s (°F)
80s
Pacific Ocean 68°
90s
Figure 3.5 Effect of a large body of water on climate.
100s
San Diego 72°
40 miles 15

16. Evaporative Cooling
Evaporation is transformation of a substance from liquid to gas. Heat is required to evaporate water (Must overcome the energy in hydrogen bonds attracting water molecules to each other)
Since a liquid uses energy to evaporate, it cools the surface, a process called evaporative cooling.
Evaporative cooling regulates and stabilizes temperatures in organisms and bodies of water
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17. Expanding water -Floating Ice on Liquid Water
Most materials contract as they solidify, but water expands.
Since d = m/v when the volume increases the density of water will DECREASE.
At 0°C, molecules lock into a crystalline lattice, Each water molecule bonds to four others.
Since ice is less dense it floats. If ice sank all bodies would eventually freeze.
During the summer, only the upper few centimeters of the ocean would thaw.
Instead surface layers of ice insulate the liquid water below, allowing life underneath to continue.
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18. Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice:
Figure 3.6
Hydrogen bond
Liquid water:
Hydrogen bonds
break and re-form
Figure 3.6 Ice: crystalline structure and floating barrier.
Ice:
Hydrogen bonds
are stable 18

19. Figure 3.6a
Figure 3.6 Ice: crystalline structure and floating barrier. 19

20. Water: The Solvent of Life
A solution is a liquid that is a homogeneous mixture of substances
A solvent is the dissolving agent of a solution
The solute is the substance that is dissolved
An aqueous solution is one in which water is the solvent
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21. Water is an effective solvent because it forms hydrogen bonds with ionic and polar covalent molecules.
Ionic compounds form hydration shell around ions.
Polar molecules form hydrogen bonds with water.
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22. Hydrophilic and Hydrophobic Substances
A hydrophilic substance is one that has an affinity for water.
Some hydrophilic substances do not dissolve because their molecules are too large. Ex. Cellulose can absorb water but won’t dissolve.
Hydrophobic substances are nonionic or contain nonpolar covalent bonds.
Hydrophobic molecules are major ingredients of cell membranes.
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23. Solute Concentration in Aqueous Solutions
Most biochemical reactions occur in water
Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution.
Concentration is measured by Molarity.
It is important to learn to calculate Molarity of a solution.
Molarity = # moles solute / Liters of solution
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24. Mole- Like a dozen, this is a quantity ( 6.02 × 1023 molecules)
Molecular mass is the sum of the masses of all atoms in a molecule. Ex: NaCl
Na = 23.0 g/ mole
Cl = 35.5 g/ mole
Molecular Mass of NaCl = 58.5 g/ mole
Mole- Like a dozen, this is a quantity
( 6.02 × 1023 molecules)
1 mole of any substance will weigh the equivalent of its molecular mass.
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25. # moles = # grams / molecular mass
Ex. 25 grams of NaCl = ? Moles
25 grams NaCl x 1 mole NaCl = moles
grams NaCl
Calculate a molarity:
What is the molarity when 25 grams of NaCl is dissolved in 500 mL of water?
M = moles = M
0.500 liters

26. Acidic and basic conditions:
A hydrogen atom in a water molecules can shift from one molecule to the other:
The molecule with the extra proton is now a hydronium ion (H3O+), though it is often represented as H+
The molecule that lost the proton is now a hydroxide ion (OH–)
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27. Water dissociates into a hydrogen ion and a hydroxide ion:
H2O <=> H+ + OH−
Concentrations of H+ and OH– are equal in pure water. This is a neutral solution.
An acid is any substance with increased H+ concentration .
A base is any substance with reduced H+ concentration.
The pH scale describes a solution as acidic or basic.
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28. pH Scale 1 2 Increasingly Acidic [H+] > [OH] 3 4 Acidic solution 51
Battery acid 2
Gastric juice, lemon juice H+ H+
OH H+
Vinegar, wine,
cola H+ 3
Increasingly Acidic
[H+] > [OH]
OH H+ H+ H+ H+ 4
Acidic
solution
Tomato juice
Beer
Black coffee 5
Rainwater 6
Urine
OH
OH
Neutral
[H+] = [OH]
Saliva
OH 7 H+ H+
Pure water
OH
OH
Human blood, tears H+ H+ H+ 8
Seawater
Neutral
solution
Inside of small intestine 9
Figure 3.10 The pH scale and pH values of some aqueous solutions. 10
Increasingly Basic
[H+] < [OH]
Milk of magnesia
OH
OH 11
OH H+
OH
OH
Household ammonia
OH H+
OH 12
Basic
solution
Household
bleach 13
Oven cleaner 14 28

29. Some acids and bases (HCl and NaOH) are strong acids or bases
Some acids and bases (HCl and NaOH) are strong acids or bases. These molecules dissociate completely in water.
Other acids and bases (NH3) are weak acids or bases. These molecules do NOT dissociate completely in water.
The internal pH of most living cells must remain close to pH 7. Buffers are substances that minimize changes in concentrations of H+ and OH– in a solution.
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30. Buffers resist changes to the pH of a solution when H+ or OH− is added to the solution.
Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted.

31. Acidification: A Threat to Water Quality
Human activities such as burning fossil fuels threaten water quality
CO2 is the main product of fossil fuel combustion
CO2 dissolved in water forms carbonic acid; this process is called acidification.
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32. The burning of fossil fuels is a major source of sulfur oxides and nitrogen oxides which react with water to form strong acids and fall back to Earth’s surface in rain or snow
Acid precipitation is rain, fog, or snow with a pH lower than It damages life in lakes and streams and alters the soil.
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