Water and the
Fitness of the
Environment
What molecule supports all
of life?
Water Cycle
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
How does the polarity of
water affect its properties?
• What is a polar molecule?
• Has polar bonds
• Water has polar covalent bonds
• Oxygen is more electronegative than H
• Electrons of covalent bonds spend more time
closer to Oxygen than to H
• Creates a polar molecule
• O region is partially negative
• H regions are partially positive
• Causes the anomalous properties of water
POLAR MOLECULE
–
O
H
+
H
H2O
+
–
HYDROGEN BONDS
+
Water
(H2O)
+
Hydrogen bond
–
Ammonia
(NH3)
+
+
+
States of Water
How does this change when
water is in different states?
• Slightly positive H of 1 molecule is attracted to
slightly negative O of nearby molecule creating a
H bond that holds those molecules together
• Hydrogen bonds by themselves are not that strong;
however, when they are continuously forming, reforming, breaking, then at any instant a large
percentage of water molecules are hydrogen-bonded
to neighbors
Water and Polarity
Hydrogen
bonds
What are the 4 Emergent
Properties of Water?
•
•
•
•
Cohesive behavior
Ability to moderate temperature
Expansion up freezing
Versatility as a solvent
What are the 4 Emergent
Properties of Water?
Cohesive Behavior
• What is cohesion?
• Molecules are linked by multiple hydrogen bonds which
make water more structured than other liquids
• Collectively, hydrogen bonds hold substance together =
Cohesion
Water and Cohesion
Water-conducting cells
100 µm
What are the 4 Emergent
Properties of Water?
Cohesive Behavior
• Contributes to transport of water and dissolved
nutrients against gravity in plants
• There exists a network of water-conducting cells help
water reach the leaves from the roots
What starts the process?
Adhesion
What are the 4 Emergent
Properties of Water?
Cohesive Behavior
• Cohesion is supported by Adhesion
• What is Adhesion?
• clinging of one substance to another
• Adhesion of water to cell walls by those same hydrogen
bonds
What are the 4 Emergent
Properties of Water?
Cohesive Behavior
• How is this related to Surface Tension?
• Surface tension= how difficult it is to stretch or break the
surface of a liquid
What are the 4 Emergent
Properties of Water?
Cohesive Behavior
• Benefits:
•
•
•
•
Bugs that walk on water
Bugs that use air bubble to breath underwater
Leads to transport of water and its dissolved nutrients
against gravity in plants
Water molecules leaving tree through evaporation
cause its H bonds to tug on water molecules in the tree
creating an upward force of water
Water and Temperature
Hydrogen
bonds
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• How does water moderate air temperature?
• By absorbing heat from the air that is warmer and
releasing stored heat to air that is cooler
• Can absorb or release a large amount of heat with only
slight change in its own temperature
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• How does this work?
1st - Have to understand what heat is:
• Heat is a form of energy
• Measure of the amount of heat is a measure of the matter’s
TOTAL kinetic energy due to motion of its molecules and
depends on matter’s volume
• The energy of motion= kinetic energy
• Related to temperature, but not same
• Temperature= measure of heat intensity that represents the
average kinetic energy of the molecules, regardless of
volume
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• How does this work?
• Water stabilizes temperatures from its relatively high
specific heat
• Specific Heat• is defined as the amount of heat that must be absorbed or lost
for 1 g of that substance to change its temperature by 1 °C
•
•
For Water- 1 calorie per gram per °C = 1 cal/g/°C
Because has high specific heat relative to other material, water
will change its temperature less when it absorbs or loses a given
amount of heat
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• How does this work?
• In order to absorb heat, bonds must be broken
• Because once one bond is broken, it can reform with
another molecule, the heat absorbed is lost through the
reforming of bonds,
• Much of the actual heat absorbed is used to break the
bonds before the molecules can begin moving faster
• Water has a high specific heat and high heat of
vaporization
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• What is Evaporative cooling?
• Molecules moving fast enough to overcome the attraction
to each other, can leave the liquid and enter the air as gas
• Called Vaporization or Evaporation
• Heat of vaporization
• Quantity of heat a liquid must absorb for 1 g of it to be
converted from liquid to the gaseous state
• High specific heat= high heat of vaporization
• Caused by the H bond
Evaporative Cooling
Evaporative Cooling in
plants
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• What is Evaporative cooling?
•
•
As liquid evaporates, the surface of the liquid that
remains behind cools down
Occurs because the “hottest” molecules with greatest
kinetic energy, are the most likely to leave as a gas
What are the 4 Emergent
Properties of Water?
Ability to Moderate
Temperature
• Benefits:
• Bodies of water maintain a constant temperature keeping its
inhabitants from going into heat shock on a hot day
• Keeps water warm on a cool day and cool on a hot day, and in turn,
cools the air around it on a hot day and heats air around it on a cool day
• Keeps temp for fluctuating greatly due to the fact that oceans cover the
earth
• Helps moderate Earth’s climate bc amount of solar heat absorbed by
tropical seas is consumed during the evaporation of surface water
• Contributes to stability of temperature in lakes and ponds and provides
mechanism that prevents terrestrial organisms for overheating
What happens to the ice?
What are the 4 Emergent
Properties of Water?
Expansion Upon Freezing
• Water is less dense as a solid than as a liquid
• Ice Floats
• Begins freezing when its molecules are no longer moving
vigorously enough to break their hydrogen bonds
• Above 4 degrees C acts like any other liquid, but below,
freezes at 0 degrees locking the water molecules in place in
their very structured arrangement
• Becomes about 10% less dense
• Creates H bonds at arms’ length from each other
• When absorbs enough heat for water to rise above 0°C
then the H bonds become disrupted
Hydrogen Bond angles
What are the 4 Emergent
Properties of Water?
Expansion Upon Freezing
• What happens after 0°C?
• Water reaches its greatest density at 4°C and begins to expand as
the molecules move faster
What are the 4 Emergent
Properties of Water?
Expansion Upon Freezing
• Benefits:
• Fish get to survive in cold temperatures
• We get cold drinks
Universal Solvent
What are the 4 Emergent
Properties of Water?
Versatility as a Solvent
• Solution• Liquid that is completely homogeneous mixture of two
or more substances
• Solvent• Dissolving agent of a solution
• Solute• Substance that is dissolved
• Aqueous solution• Solution in which water is the solvent
Solution
Suspension
Colloid
This is why you should
shake milk first
What are the 4 Emergent
Properties of Water?
Versatility as a Solvent
• Why is water such a versatile solvent?
• Due to polarity of the ions
• Ions have mutual affinity through electrical attraction of
the opposite charges
• For this reason, water molecules surround the individual
ions, separating and shielding them from one another,
creating a hydration shell
• Hydration shell- sphere of water molecules around each
dissolved ion
• Compounds don’t have to be ionic to dissolve water
• Dissolve when water molecules surround each of the
solute molecules, forming hydrogen bonds with them
What are the 4 Emergent
Properties of Water?
Versatility as a Solvent
• It’s ability to be such a great solvent, led to
the creation of the two terms:
• Hydrophilic
•
•
Any substance that has an affinity for water
Can be hydrophilic without dissolving• Substances that are suspended in the aqueous solution
create mixtures called: colloid
• Stable suspension of fine particles in a liquid
• Hydrophobic
•
•
•
Any substance that does not have an affinity for water
Generally substances that are nonionic and nonpolar
Seems to repel water
What are the 4 Emergent
Properties of Water?
Versatility as a Solvent
•Benefits:
• Allows the movement of solvents through cohesion
• Makes the solvent hydrophilic, benefitting cellular
processes
How can you determine how
many atoms and molecules
are involved and present in an
aqueous solution?
• Use mass to calculate the number of molecules
• Process:
• Know:
• Mass of each atom in molecule
• Calculate:
• Molecular Mass
• Sum of masses of all the atoms in a molecule
many atoms and molecules
are involved and present in an
aqueous solution?
• Example:
• C6H12O6 = Glucose
• (12 daltons) x 6 + (1 daltons) x 12 + (16 daltons) x 6 =
72+12+96 = 180 daltons
• Glucose has a molecular mass of 180 daltons
• Not practical to measure out 1 molecule of something, instead we
use mole
How can you determine how
many atoms and molecules are
involved and present in an
aqueous solution?
• Know:
• Mole = (mol) = represents an exact number of objects –
6.02 x 1023
• 6.02 x 1023 = Avogadro’s number
• There are 6.02 x 1023 daltons in 1 gram
• Calculate :
• Molar mass
• Use the molecular mass to determine the grams of the
molecule to give 6.02 x 1023 molecules of the substance = 1
mol of the substance
How can you determine how many
atoms and molecules are involved
and present in an aqueous solution?
• Example:
• Glucose has a molecular mass of 180 daltons
• Therefore, there are 180 grams for 1 mol of glucose
• What is the point of this?
• If you want to make a 1:1 mixture of something, using mol
makes it easier to create that mixture because you can’t just
mix 10 grams of one and 10 grams of the other because it
might not represent a 1:1 molecular mixture because the
molecules have different weights
How can you determine how
many atoms and molecules
are involved and present in an
aqueous solution?
• What if you wanted to make a solution?
• Determine the molar mass and add enough water to
bring the total volume of the solution up to 1 L = 1
Molar solution
• Molarity= the number of moles of solute per liter of
solution
What are Acids and
Bases?
• Hydrogen ion-
• H+
• Occurs when a hydrogen atom participating in a
hydrogen bond between two water molecules shifts
from one molecule to the other
• Hydrogen atom leaves it electron behind
• what is actually transferred is a hydrogen atom with a
positive charge
• a single proton with a charge of +1
What are Acids and
Bases?
• hydroxide ion –
• OH• The water molecule that lost the proton
• Has a charge of 1-
What are Acids and
Bases?
• Hydronium ion –
• H30+
• Occurs when the proton binds to another water
molecule
• This reaction is reversible
What are Acids and
Bases?
• Overall, what effect does this have?
• H+ does not exist solitarily, always associated with
another water molecule
• The reversible reaction is generally at a dynamic
equilibrium when water molecules dissociate at the
same rate that they are being re-formed from H+ and
OH• These concentrations are equal in pure water
• By themselves, H+ and OH- are very reactive
• Adding solutes (Acids and Bases) disrupt the balance
present in pure water
What are Acids and
Bases?
• Acids
• Acidic
• When dissolve in water, donate additional H+ to solution
• Substance that increases the hydrogen ion concentration of a
solution
• Example:
• Hydrochloric acid (HCl)
What are Acids and
Bases?
• Acids
• Strong Acids• Compounds that dissociate completely when mixed with water
to increase the concentration of H+
• Represented as a single arrow
• Weak Acids• Compounds that DO NOT dissociate completely when mixed
with water, but still increase the concentration of H+
• Represented as a double sided arrow
• Accept back the Hydrogen ions
What are Acids and
Bases?
• Bases
•
•
•
•
Basic
Reduces the hydrogen ion concentration of a solution
Have higher concentrations of OH- than H+
Some reduce H+ concentration by directly accepting
hydrogen ions
• Example:
• Ammonia
• Others reduce H+ concentration indirectly by dissociating
to form hydroxide ions that combine with the H+ to form
water
• Example:
• Sodium hydroxide
What are Acids and
Bases?
• Bases
• Strong base• Compounds that dissociate completely when mixed with
water to increase the concentration of OH• Represented as a single arrow
• Weak Bases• Compounds that DO NOT dissociate completely when mixed
with water, but still increase the concentration of OH• Represented as a double sided arrow
• Will release back the Hydrogen ions
What are Acids and
Bases?
• Neutral solutions
• H+ and OH- are equal
What is pH? What exactly
does it measure?
• At any aqueous solution at 25°C, the product of
the hydrogen and hydroxide ion concentrations
is constant at 10-14
• [H+][OH-] = 10-14
• Neutral solutions =
• [H+] = 10-7 and [OH-] = 10-7
• 10-7 x 10-7 = 10-14
What is pH? What exactly
does it measure?
• What if:
• [H+] = 10-5 (therefore, the number of H+ ion
increases_?
10-5 x 10-? = 10-14
What is pH? What exactly
does it measure?
• pH scale compresses the range of H+ and OHconcentrations by employing the logarithmic scale
using logarithms
What is pH? What exactly
does
it
measure?
• the pH is defined as the negative logarithm (base 10)
of the hydrogen ion concentration:
• pH = - log [H+]
• Neutral =
• –log 10-7 = -(-7)= 7
• pH of 7
• Acid =
• pH declines as the H+ concentration increases
• pH of less than 7
• Base =
• pH of greater than 7
What is pH? What exactly
does it measure?
• based on H+ concentrations while implying OHconcentrations
• each pH unit represents a tenfold difference in H+
and OH- concentrations
What is a Buffer?
• Help maintain a relatively constant pH in biological
fluids despite the addition of acids or bases
• Substances that minimize changes in the
concentration of H+ and OH- in a solution when they
have been depleted
• Most contain a weak acid and its corresponding base
• These combine reversibly with hydrogen ions
• The chemical equilibrium created by buffers acts as
a pH regulator in which the reaction shifts left or
right as other processes in the solution add or
remove hydrogen ions
Buffering by Bicarbonate
in blood
What is a Buffer?
• Example:
• If the H+ concentration falls (increase in pH), the
reaction shifts right
Why are buffers
important?
• Even a slight change in pH can be harmful, because
the chemical processes of the cell are very sensitive to
the concentration of hydrogen and hydroxide ions
How can all of this information
affect our water quality on Earth?
• Most life is dependent on water
• Actions:
• Burning of fossil fuels
• Releases gaseous compounds into the atmosphere,
including copious amounts of CO2 which alter the delicate
balance of conditions of life on Earth by affecting water pH
and temperature. Major source of sulfur oxides and nitrous
oxides that react with water in the air to form strong acids
which fall to the Earth as rain or snow
Acid Rain Source
Acid rain effects on plants
Acid Rain and Concrete
How can all of this information
affect our water quality on Earth?
• Results:
• Acid precipitation- rain, snow, and fog with pH lower than
5.2
• Carried by wind can affect not just the polluted areas, but
also area miles away
• Can affect the water supply
• Can have adverse effects on land by affecting the soil
chemistry
• Effected many North American and European forests
How can all of this information
affect our water quality on Earth?
• Results:
• CO2 is the main produce of fossil fuel combustion
• It’s released into the atmosphere, and ½ stays in the
atmosphere
• Acts like reflective blanket that prevents heat from radiating
into outer space
• Causes the greenhouse effect
• Some is taken up by trees, but about 30% is absorbed by the
ocean
• Can harm marine life and ecosystems
• Reacts with water to form carbonic acid which dissociates,
producing protons and a balance between bicarbonate and
carbonate
• This process can affect the production of calcium carbonate
by corals – needed for calcification in coral reefs