Water and the Fitness of the Environment

Water and the Fitness

of the Environmen

t

What molecule supports all of life?

Water Cycle

Transportover land

Precipitationover landEvaporation

from oceanPrecipitationover ocean

Net movement ofwater vapor by wind

Solar energy

Evapotranspirationfrom land

Runoff andgroundwater

Percolationthroughsoil

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

H

O

H

H2O+ +

–

HYDROGEN BONDS –

Water(H2O)

Ammonia(NH3)

Hydrogen bond

+

+

–

+

+

+

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, re-forming, breaking, then at any instant a large percentage of water molecules are hydrogen-bonded to neighbors

Water and Polarity

Hydrogenbonds

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


• 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


• 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


•How is this related to Surface Tension?• Surface tension= how difficult it is to stretch or

break the surface of a liquid


• 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

Hydrogenbonds


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



• 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



• 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



• 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 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 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



• 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?


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 happens after 0°C?• Water reaches its greatest density at 4°C and begins to

expand as the molecules move faster



• Benefits:• Fish get to survive in cold temperatures• We get cold drinks

Universal Solvent


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

ColloidThis is why you should shake milk

first



• 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



• 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



• 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



• 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



• 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


• hydroxide ion –• OH-• The water molecule that lost the proton• Has a charge of 1-


• Hydronium ion –• H30+

• Occurs when the proton binds to another water molecule

• This reaction is reversible


• 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


• 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)


• 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


• 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


• 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


• 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

OH- concentrations 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

OH- concentrations• 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

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Water and the Fitness of the Environment