Chapter 3: Water. Water: The Molecule That Supports All of Life Water is the biological medium here...
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Transcript of Chapter 3: Water. Water: The Molecule That Supports All of Life Water is the biological medium here...
Chapter 3: Water
Water: The Molecule That Supports All of Life
• Water is the biological medium here on Earth• All living organisms require water more than any other
substance• ¾ of the Earth’s surface is submerged in water• The abundance of water is the main reason the Earth is
habitable
Properties of Water
• The polarity of water molecules• Allows them to form hydrogen bonds with each other• Contributes to the various properties water exhibits that
make life as we know it possible
Hydrogenbonds
+
H
H+
+
–
–
– –
Properties of Water
• Cohesion• Is the bonding of like polar molecules to
neighboring like polar molecules• Is due to hydrogen bonding
Properties of Water
• Adhesion• Is the bonding of polar molecules to unlike
neighboring polar molecules• It is also due to hydrogen bonding
Cohesion and Adhesion
Capillary action
Cohesion and Adhesion
Heat and Temperature
• Kinetic Energy• Is the energy of motion• Heat is the measure of the total amount of
kinetic energy due to molecular motion• Temperature measures the intensity of heat
Specific Heat
• Specific Heat• Is the amount of heat that must be absorbed or
lost for 1 gram of that substance to change its temperature by 1ºC
• Water has a high specific heat, due to hydrogen bonding, which allows it to minimize temperature fluctuations• Heat is absorbed when hydrogen bonds break• Heat is released when hydrogen bonds form
Specific Heat
• Simply put:• If you add heat to water, it will be get
warmer slower compared to a liquid without hydrogen bonds
• If you take away heat from water, it will cool slower compared to other liquids
San Diego 72°
40 miles
Pacific Ocean70s (°F)
80s
90s
100s
Santa Barbara 73°Los Angeles (Airport) 75°
Burbank90°
San Bernardino100°Riverside 96°
Santa Ana 84° Palm Springs
106°
Specific Heat
Evaporative Cooling
• Evaporation• Is the transformation of a substance from a liquid to a gas• For water, H bonds BETWEEN water molecules must be broken for evaporation to occur
• Evaporative cooling• Is due to the molecules with the most kinetic energy entering the gas state, leaving behind those with less
energy • This phenomenon can cool biological organisms• Evaporation is impeded by high humidity however
Expression: It’s not the heat but the humidity!
Ice
• Solid water, or ice• Is less dense than liquid water• Floats in liquid water
• Since ice floats in water• Life can exist under the frozen surfaces of lakes and
polar seas
Ice
• The hydrogen bonds in ice are more “ordered” than in liquid water, making ice less dense
• In same space, fewer water molecules can fit when frozen compared to liquid water
Liquid water
Hydrogen bonds constantly break and re-form
Ice
Hydrogen bonds are stable
Hydrogen bond
Water: Solvent of Life
• Water is a versatile solvent due to its polarity
• It can form aqueous solutions
Water as a Solvent
The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them
+
+
+
+Cl –
–
–
–
–
Na+
++
+
+
–
–
–
–
–
–Na+
Cl–
++
--
--
-
+
++ +
++
+ +
Water as a Solvent
• A solution is a liquid homogenous mixture of 2 or more substances
• The solute is the substance that is dissolved in a solution
• The solvent is the dissolving agent of a solution, often water (aqueous)
Water as a Solvent
• A hydrophilic substance
• Does have an affinity for water
• Typically contains polar covalent or ionic bonds
• A hydrophobic substance
• Does not have an affinity for water
• Typically contains non-polar covalent bonds (like fats/oil)
• Expression: Oil and water (don’t mix); Meaning incompatible things or people (can’t be made to work well together)
pH
• Water can break apart into hydrogen ions (H+) and hydroxide ions (OH-)
• Changes in the concentration of these ions can have a great affect on living organisms
pH
• The pH of a solution• Is determined by the concentration of hydrogen
ions, [H+] • [H+] high in an acid• [H+] low in a base
pH = -log[H+]
• e.g. A solution with [H+] = 1 x 10-
5M would have a pH value of 5
Acids and Bases
• An acid• Is any substance that increases the H+
concentration of a solution
• A base• Is any substance that reduces the H+
concentration of a solution
pH Scale
• pH scale is from 0-14• Solutions with
• pH values < 7 are acids• pH values = 7 are neutral• pH values > 7 are bases
Incr
easi
ng
ly A
cid
ic[H
+]
> [
OH
– ]In
creasi
ng
ly B
asic
[H+]
< [
OH
– ]
Neutral[H+] = [OH–]
Oven cleaner
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
pH Scale
Battery acid
Digestive (stomach) juice, lemon juiceVinegar, beer, wine,colaTomato juice
Black coffee RainwaterUrine
Pure waterHuman blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
pH Scale
• For example, a testing kit indicates a pH level of 3 in a solution. This means:• The solution is an acid• The [H+] = 1 x 10-3M or 0.001M
• Another solution measures pH 9. This means:• The solution is a base• The [H+] = 1 x 10-9M or 0.000000001M
• pH3 has more H+ than pH 9 (0.001M > 0.000000001M)
Pretend iClicker ?
The concentration of H+ ions in a solution is 1 x 10-
8M. This tells you the pH of the solution is
A.pH 8, and it is an acid.
B.pH 8, and it is a base.
C.pH 6, and it is an acid.
D.pH 6, and it is a base
E.pH 14, and it is an acid.