Transcript video slide - Saginaw Valley State University

Chapter 3:
Water & Life
A view of earth from space, showing our planet’s
abundance of water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 3.1: Polar covalent bonds in water
molecules result in hydrogen bonding
• The water molecule is a polar molecule: the
opposite ends have opposite charges
• Polarity allows water molecules to form hydrogen
bonds with each other
© 2011 Pearson Education, Inc.
Figure 3.2 Hydrogen bonds between water molecules
–
+
Hydrogen
bonds
H
+
–
H
–
+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
+
–
Concept 3.2: Four emergent properties of
water contribute to Earth’s suitability for
life
• Four of water’s properties that facilitate an
environment for life are
– Cohesive behavior
– Ability to moderate temperature
– Expansion upon freezing
– Versatility as a solvent
© 2011 Pearson Education, Inc.
Water transport in plants (cohesion)
Water conducting cells
100 µm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Surface tension is a measure of how hard it is
to break the surface of a liquid
• Surface tension is related to cohesion
© 2011 Pearson Education, Inc.
Figure 3.4
Water’s Ability to Moderate Temperature
• Water needs to give away energy in form of heat when it goes
from gas to liquid, and from liquid to solid. The opposite is also
true: water needs to take energy in form of heat when going
from solid to liquid or liquid to gas.
• Water is special in its need to absorb or expend a LARGE
AMOUNT of heat to change form.
• The latter is the reason we perspire: evaporating water cools
down our skin.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ice: crystalline structure and floating barrier
Hydrogen
bond
Ice
Liquid water
Hydrogen bonds are stable
Hydrogen bonds
constantly break and re-form
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A crystal of table salt dissolving in water (use as a solvent)
Negative
Oxygen regions
of polar water
molecules are
attracted to sodium
cations (Na+).
Positive
hydrogen regions
of water molecules
cling to chloride
anions (Cl–).
–
Na+
+
–
+
–
–
Na+
+
Cl–
Cl –
–
+
–
–
+
+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
+
–
+
–
–
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
© 2011 Pearson Education, Inc.
Reaction producing hydroxide and hydronium ions
–
+
H
H
H
H
H
H
H
Hydronium
ion (H3O+)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
+
H
Hydroxide
ion (OH–)
Figure 3.10
H+
H+
 H+
H+ OH
+

OH H H+
+
H H+
Acidic
solution
Increasingly Acidic
[H+] > [OH]
pH Scale
0
1
Battery acid
2
Gastric juice, lemon juice
3
Vinegar, wine,
cola
4
Tomato juice
Beer
Black coffee
5
6
Neutral
solution
OH
OH
OH H+ OH

OH OH
OH
+
H
Basic
solution
Neutral
[H+] = [OH]
7
8
Increasingly Basic
[H+] < [OH]
OH
OH
H+ H+ OH

OH OH +
H+ H+ H
Rainwater
Urine
Saliva
Pure water
Human blood, tears
Seawater
Inside of small intestine
9
10
Milk of magnesia
11
Household ammonia
12
13
Household
bleach
Oven cleaner
14
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
• About 25% of human-generated CO2 is
absorbed by the oceans
© 2011 Pearson Education, Inc.
• The burning of fossil fuels is also a major source
of sulfur oxides and nitrogen oxides
• These compounds react with water in the air to
form strong acids that fall in rain or snow
• Acid precipitation is rain, fog, or snow with a ph
lower than 5.2
• Acid precipitation damages life in lakes and
streams and changes soil chemistry on land
© 2011 Pearson Education, Inc.
Figure 3.9 Acid precipitation and its effects on a forest
0
1
More
acidic
2
3
4
5
6
Acid
rain
Normal
rain
7
8
9
10
11
12
13
14
More
basic
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings