View
1.700
Download
0
Category
Preview:
DESCRIPTION
Water, Polarity, etc.
Citation preview
1
Water and the Fitness of
the Environment
2
Importance of water
• Overview: 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
3
Water Facts
• The polarity of water molecules results in hydrogen bonding
• The water molecule is a polar molecule
4
Water’s Polarity• The polarity of water molecules
– Allows them to form hydrogen bonds with each other
– Contributes to the various properties water exhibits
Hydrogenbonds
+
+
H
H+
+
–
–
– –
Figure 3.2
5
Properties of water
• Four emergent properties of water contribute to Earth’s
fitness for life
1. Cohesion - Like molecules bonding to each other (water
attracting other water molecules)
Water conducting
cells
2. Surface tensionIs a measure of how hard it is to break the
surface of a liquid
3. Water moderates air temperature because it has a high specific heat, which allows
it to minimize temperature fluctuations to within limits that
permit life
4. Water is a versatile solvent due to its polarity
6
Insulation of Bodies of Water by Floating Ice
• Solid water, or ice– Is less dense than liquid water– Floats in liquid water
Life can exist under the frozen surfaces of lakes and polar seas
7
• The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve themNegative
oxygen regions
of polar water
molecules are
attracted to sodium
cations (Na+).
+
+
+
+Cl –
–
–
–
–
Na+Positive hydrogen regions
of water molecules cling to chloride anions
(Cl–).
++
+
+
–
–
–
–
–
–Na+
Cl–
Figure 3.6
8
Hydrophilic and Hydrophobic Substances
• A hydrophobic substance– Does not have an affinity for water
• A hydrophilic substance– Has an affinity for water
9
Acids and Bases
• Dissociation of water molecules leads to acidic and basic conditions that affect living organisms
• Organisms must maintain homeostasis in the pH of their internal and external environments
10
• Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions
• Changes in the concentration of these ions Can have a great affect on pH in living organisms
H
Hydroniumion (H3O+)
H
Hydroxideion (OH–)
H
H
H
H
H
H
+ –
+
Figure on p. 53 of water dissociating
Effects of Changes in pH
11
Acids and Bases
• An acid– Is any substance that increases the
hydrogen ion concentration of a solution• A base
– Is any substance that reduces the hydrogen ion concentration of a solution
12
The pH Scale• Scale goes from 0-14 with 7 neutral• The pH of a solution Is determined by the
relative concentration of hydrogen ions
• Difference of 10X in hydrogen ion concentration between any two pH values
• Acids have a higher number of H+ ions than a base
• Acids produce H+ ion in solution• Bases produce OH- ions in solution
13
The pH scale and pH values of various aqueous solutions
Incr
easi
ngly
Aci
dic
[H+]
> [
OH
–]
Incr
easi
ngly
Bas
ic[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
Figure 3.8
14
Buffers
• The internal pH of most living cells– Must remain close to pH 7
• Buffers– Are substances that minimize changes
in the concentrations of hydrogen and hydroxide ions in a solution
– Consist of an acid-base pair that reversibly combines with hydrogen ions
– Made by organisms
15
• Acid precipitation– Can damage life in Earth’s ecosystems
0
12
34
56
78
910
11
12
1314
Moreacidic
Acidrain
Normalrain
Morebasic
Figure 3.9
16
Moles and Molarity
• A mole– Represents an exact number of
molecules of a substance in a given mass
• Molarity– Is the number of moles of solute per liter
of solution
17
1 In the beginning God created the heavens and the earth. 2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.
God created water before life
Recommended