 Chapter 3: Water and the Fitness of the Environment
 Overview: The Molecule That Supports All of Life
• Water is the ___________________________ on Earth
• All living organisms __________________ more than any other substance
• Most cells are ________________________, and cells themselves are about
__________________
• The abundance of water is the main reason the Earth is _______________
• _______ of Earth’s surface is submerged in water
– Most is liquid
– Ice and vapor also present
– Life began in water and evolved for 3 billion years before spreading onto land
– The properties of water allow it to support and maintain living systems.
 Concept 3.1: The polarity of water molecules results in hydrogen bonding
• The water molecule is a _____________________: The opposite ends have opposite
charges
• ___________ allows water molecules to form ___________________ with each
other
• Hydrogen bonds constantly break and reform
 Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life
• Four of water’s properties that facilitate an environment for life are:
– ____________________________________
– ____________________________________
– ____________________________________
– ____________________________________
• They are the result of hydrogen bonding
 Cohesion
• Collectively, hydrogen bonds hold water molecules together, a phenomenon
called _________________
• Cohesion helps the _________________________________ in plants
• _____________ is an attraction between _______________ substances, for
example, between water and plant cell walls
• ______________________ is a measure of how hard it is to break the surface
of a liquid.
• Water has a greater surface tension than most other liquids.
• Surface tension is ____________________________
 Moderation of Temperature
• Water _____________ heat from warmer air and ______________ stored heat
to cooler air
• Water can absorb or release a large amount of heat with only a
____________________ in its own temperature
• Heat and Temperature
– ________________________ is the energy of motion
– __________ is a measure of the _______________________
__________________due to molecular motion
– ________________________ measures the intensity of heat due to the
average kinetic energy of molecules
– The ______________________ is a measure of temperature using
Celsius degrees (°C)
– A _________________ is the amount of heat required to raise the
temperature of ____________________________
– The “calories” on food packages are actually _______________ where
________________________
– The _______________ is another unit of energy where
______________________________________
• Water’s High Specific Heat
– The ______________________ of a substance is the amount of heat
that must be absorbed or lost for ____________________
__________________________________
– The ______________________________________
– Water resists changing its temperature because of its
_____________________________________
o This is why a pot gets hotter faster than the water inside it.
– Water’s high specific heat can be traced to hydrogen bonding
o Heat is _________________________________________
o Heat is _________________________________________
– The high specific heat of water __________________________
_________________________ to within limits that permit life
• Evaporative Cooling
– __________________ is transformation of a substance from
_______________________. Some evaporation occurs _____
____________________. If a liquid is heated, the average kinetic
energy increases and evaporation happens faster.
– _________________________ is the heat a liquid must absorb for
________________________. Water has a high heat of vaporization.
o
(580 cal to evaporate 1g at 25 )
– As a liquid evaporates, its remaining surface cools, a process called
________________________________
– Evaporative cooling of water helps stabilize temperatures in organisms
and bodies of water
 Insulation of Bodies of Water by Floating Ice
• Ice floats in liquid water because hydrogen bonds in ice are more
“___________,” making ice _______________
• Water reaches its __________________________
• If ice sank, all bodies of water would eventually freeze solid, making life
impossible on Earth
 The Solvent of Life
• A ____________ is a liquid that is a homogeneous mixture of substances
• A ____________ is the dissolving agent of a solution
• The ___________ is the substance that is dissolved
• An ________________________ is one in which water is the solvent
• Hydration shell
– Water is a ______________________________________, which allows
it to form hydrogen bonds easily
– When an ionic compound is dissolved in water, each ion is surrounded
by a sphere of water molecules called a _______________________
– Water can also dissolve compounds made of ______________
________________________, such as ______________
– Even large polar molecules such as ______________ can dissolve in
water if they have ionic and polar regions
• Hydrophilic and Hydrophobic Substances
– A __________________ substance is one that has an affinity for water
(“water loving”)
– A __________________ substance is one that does not have an affinity
for water (“water fearing”)
– _______ molecules are hydrophobic because they have relatively
_________________________
– A __________ is a stable suspension of fine particles in a liquid
• Solute Concentration in Aqueous Solutions
– Most ___________________________________ occur in water
– Chemical reactions depend on collisions of molecules and therefore on
the _________________________________ in an aqueous solution
– ________________________ is the sum of all masses of all atoms in a
molecule
o Ex: Sucrose (C H O )
12 22
11
mass of a Carbon atom is ________
mass of a Hydrogen atom is ______
mass of an Oxygen atom is _______
o Thus, molecular mass of sucrose is __________________
o Because weighing out a small number of molecules is usually
impractical, numbers of molecules are usually measured in moles,
where _______________________________________, which is
Avogadro’s number
o Avogadro’s number and the unit dalton were defined such that
______________________________________
o What this means is that the molecular mass of a molecule can be
used with the unit gram, to represent the mass of
23
6.02 10 molecules of the substance. (1 mol)
o So to get 1 mol of sucrose, we weigh 342 g.
– _________________________ is the number of moles of solute per liter
of solution
o So to get a 1 molar (1M) solution of sucrose, we would weigh 342
grams and dissolve it in 1 liter of water.
o The advantage of measuring in moles is that a mole of one
substance has exactly the _____________________ as a mole of
any other substance
 Concept 3.3: Acidic and basic conditions affect living organisms
• A hydrogen atom in a hydrogen bond between two water molecules
_____________________________________
– The hydrogen atom _____________________ behind and is transferred
as a __________, or ______________________
– The molecule with the extra proton is now a ______________________
though it is often represented as ___
– The molecule that lost the proton is now a _________________
• Water is in a state of ________________________ in which water molecules
dissociate at the same rate at which they are being reformed
• Though _____________________, the dissociation of water molecules has a great
effect on organisms
+
–
• Changes in concentrations of H and OH can drastically _____________
__________________________of a cell
• Effects of Changes in pH
– Concentrations of ______________________________________
– Adding certain ___________, called _______________________, modifies
+
–
the concentrations of H and OH
– Biologists use something called the ___________________ to describe
whether a solution is acidic or basic (the opposite of acidic)
• Acids and Bases
– An __________ is any substance that _________________________ of a
solution
– A ____________ is any substance that ________________________ of a
solution
• The pH Scale
+
–
– In any aqueous solution at 25°C the product of H and OH ________________
+
and can be written as
–
–14
[H ][OH ] = 10
– So in a neutral solution: 10
-7
-7
-14
x 10 = 10
+
-5
– In an acidic solution where the concentration of H increases to 10 ; then the
-
-9
-5
-9
-14
concentration of OH must decline to 10 (10 X 10 = 10 )
-4
– What would the concentration of H+ be if the concentration of OH- is 10 ?
Answer: ______________________
– The _______ of a solution is defined by the negative logarithm of the H
concentration, written as: __________________
– For a neutral aqueous solution:
– pH always ______________ as ______________________
+
+
-
– Also, the pH number is based on H concentration, and implies OH concentration.
-10
– Example: A pH10 has an hydrogen ion concentration of 10 M and a hydroxide
-4
ion concentration of 10 M
– ______________ solutions have pH values __________________
– _______________ solutions have pH values _________________
– Most biological fluids have ____________________________________
• Buffers
– The __________________ of most __________________ must
_____________________________
– _______________ are substances that minimize changes in concentrations of H
–
and OH in a solution Most buffers consist of an
__________________________________________________
• Threats to Water Quality on Earth
– _________________________ refers to rain, snow, or fog with a
_____________________________
– Acid precipitation is caused mainly by the mixing of different pollutants with
water in the air and can fall at some distance from the source of pollutants
– Acid precipitation can damage life in lakes and streams
+
– Effects of acid precipitation on soil chemistry are contributing to the decline of
some forests
– An important buffer system in your body is the one that regulates blood pH.
– It involves _________________ (H2CO3) and _________________. Carbonic acid
forms when CO2 reacts with water in blood plasma. It dissociates to yield a
-
+
bicarbonate ion (HCO3 ) and a hydrogen ion (H )
– So: if blood pH rises, which direction will this reaction go?
Answer: ______________________
• Human activities such as _______________________________ threaten water quality
• _________is released by fossil fuel combustion and contributes to:
– A warming of earth called the _________________________
– Acidification of the oceans; this leads to a decrease in the ability of
__________________________________
You should now be able to:
1. List and explain the four properties of water that emerge as a result of its ability to form
hydrogen bonds
2. Distinguish between the following sets of terms: hydrophobic and hydrophilic
substances; a solute, a solvent, and a solution
3. Define acid, base, and pH
4. Explain how buffers work