Unit 1 Ch.3 HUnit 1 Ch.3 H22O & the fitness O & the fitness

of the Environment.of the Environment.

Presented by Mrs. Knopke

Fullerton Science Dept.

Ch. 3 NotesCh. 3 Notes

Water contributes to the fitness of the environment to support life.

Life on earth probably evolved in water. Living cells are 70%-95% H2O. Water covers about ¾ of the earth. In nature, water naturally exists in all three physical

states of matter- solid, liquid, and gas.

I. Water molecules and I. Water molecules and hydrogen bonding.hydrogen bonding.

Four valence orbitals of O point to corners of a tetrahedron.

2 corners are orbitals with unshared pairs of electrons and weak negative charge.

2 corners are occupied by H atoms which are in polar covalent bonds with O. Oxygen is so electronegative, that shared electrons spend more time around the O causing a weak positive charge near H’s.

I. Cont.I. Cont.

Positively charged H of one molecule is attracted to the negatively charged O of another water molecule.

Each water molecule can form a maximum of four hydrogen bond with neighboring water molecules.

Hydrogen bonding orders water into a higher level of structural organization.

Water has a variety of unusual Water has a variety of unusual properties because of attractions properties because of attractions between these polar molecules.between these polar molecules.

II.A. Liquid water cohesive.II.A. Liquid water cohesive.

Cohesion: phenomenon of a substances being held together by hydrogen bonds.

Through hydrogen bonds are transient, enough, water molecules are hydrogen bonded at any given time to give water more structure than other liquids.

Contributes to upward water transport in plants by holding the water column together.

Cohesion Cohesion among water molecules plays a key among water molecules plays a key role in the transport of water against gravity in role in the transport of water against gravity in

plants.plants.

Adhesion,Adhesion, clinging of one substance to another clinging of one substance to another

II.A. Cont.II.A. Cont.

Surface tension: Measure of how difficult it is to stretch or break the surface of a liquid.

Water has a greater surface tension then most liquids. Function of the fact that at the air/ H2O interface, surface water

molecules are hydrogen bonded to each other and to the water molecules below.

Causes H2O to bead (shape with smallest area to volume ratio and allows maximum hydrogen bonding).

Adhesion: Clinging of water to hydrophilic substances (e.g. glass)

Surface tension,Surface tension, a measure of the force a measure of the force necessary to stretch or break the surface necessary to stretch or break the surface

of a liquid, is related to cohesion.of a liquid, is related to cohesion.

II.B. Water has a high specific II.B. Water has a high specific heat. heat.

Kinetic energy: The energy of motion.

Heat: Total kinetic energy due to molecular motion in body of matter.

Calorie (cal): Amount of heat it takes to raise temperature of one gram of water by one degree Celsius.

Kilocalorie: (Kcal or Cal): Amount of heat required to raise the temperature of one kilogram of water by one degree Celsius.

Temperature: Measure of heat intensity due to average kinetic energy of molecules in a body of matter.

II.B. Cont.II.B. Cont.

Celsius scale Scale conversion

100.C (212

.F) = Water boils

37.C (98.6

.F) = Human body

temp.

23.C (72

.F) = Room temp.

0.C (32

.F) = Water freeze

C. =

5( F – 32)

9

F = 9 5C +32

K = C + 273

Specific Heat of waterSpecific Heat of water

Specific heat = Amount of heat that must be absorbed or lost for one gram of a substance to change it’s temperature by one degree Celsius.

Specific heat of Water = One calorie per gram per degree (1cal/g/ C)

How Water Stabilizes How Water Stabilizes Temperature:Temperature:

Hydrogen bonding among water molecules(it takes relatively large heat loss or gain for

each 1 C change in temperature.Hydrogen bonds must absorb heat to break,

and they release heat when they formMuch absorbed heat energy is used to

disrupt H-bonds before water molecules can move faster (increase temperature)

When water reaches 0When water reaches 0ooC, water becomes C, water becomes locked into a crystalline lattice with each locked into a crystalline lattice with each molecule bonded to to the maximum of molecule bonded to to the maximum of

four partners.four partners.

A large body of water can act A large body of water can act as a heat sink:as a heat sink:

Water, which covers ¾ of the planet, keeps temperature fluctuations within a range suitable for life.

Coastal areas have milder climates than inland

The marine environment has a relatively stable environment

Water has a high heat of Water has a high heat of vaporization:vaporization:

Vaporization = Transformation from liquid to gas.

- molecules with enough kinetic energy to overcome the mutual attraction of molecules in a liquid, can escape into the air.

Heat of Vaporization:Heat of Vaporization:

Quantity of heat a liquid must absorb for 1g of H2O to be converted to the gaseous state.

-For water molecules to evaporate, hydrogen bonds must be broken increase heat energy.

Water has a relatively high heat of vaporization (540 cal/g)

Evaporative cooling:Evaporative cooling:

Cooling of a liquid’s surface when a liquid evaporates

-The surface molecules with the highest kinetic energy are most likely to escape into gaseous form: the average kinetic energy in the remaining surface moleculeis lowered.

Water’s high heat of Water’s high heat of vaporization:vaporization:

Earth:

- Solar heat absorbed by tropical seas dissipates when surface water evaporates (evaporative cooling)

- As moist tropical moves towards the poles, water vapor releases heat and condenses into rain.

Water expands when it Water expands when it freezes:freezes:

Water contracts as it cools to 4 C As water cools from 4 C to freezing (O C) it

expands and becomes less dense than liquid water (ice floats)

When water begins to freeze, the molecules do not have enough kinetic energy to break H-bonds

As crystalline lattice forms, each water molecule forms a max of 4 H-bonds. Keeping molecules further apart compared to the liquid state. Thus less dense

Expansion of water Expansion of water contributes to the fitness of contributes to the fitness of

the environment for lifethe environment for life Prevents deep bodies of water from freezing solid

from the bottom up Since ice is less dense it forms on the surface first.

As it freezes it releases heat to the water below and insulates.

Makes transition between seasons less abrupt. H-bonds form = released heat H-bonds break = absorbed heat

The surface area of ice insulates liquid water The surface area of ice insulates liquid water below, preventing it from freezing and allowing below, preventing it from freezing and allowing

life to exist under the frozen surface. life to exist under the frozen surface.

Water a Versatile SolventWater a Versatile Solvent

Solution = A liquid that is homogenous mixture of two or more substances

Solvent = dissolving agentSolute = substance dissolved in the solutionAqueous solution = Solution in which water

is the solvent

Water is an effective solvent because it so Water is an effective solvent because it so readily forms hydrogen bonds with readily forms hydrogen bonds with

charged and polar covalent molecules.charged and polar covalent molecules.

Water as a solvent:Water as a solvent:

Ionic compounds – Charged regions of polar water molecules have an electrical attraction.

-Water surrounds individual ions, separating and shielding them from one another.

Polar compounds – Charged regions of polar H2O molecules have an affinity for oppositely charged regions of other polar molecules.

Nonpolar – Not water soluble ex. fats

Water loving or HatingWater loving or Hating

Hydrophilic = (hydro = water, philo = loving) Property of having an affinity for water ex. Ionic and polar

Hydrophobic = (hydro = water, phobos = fearing) Property of not having an affinity for water , and thus not being water soluble ex. nonpolar

Aqueous solutions: Acids and Aqueous solutions: Acids and BasesBases

At Equilibrium – the number of H+ ions = number of OH- ions

[H+ ] = [OH-]

Acid vs BasesAcid vs Bases

ACID

Substance the increases the relative [H+] of a solution

Also removes OH- because it tends to combine with H+ to form H2O.

For example: (in water)

HCl H+ + Cl-

Base Substance that reduces the

relative [H+] of a solution May alternately increase

OH-

Ex. A base may reduce [H+] directly:

NH3 + H+ NH4+

May reduce indirectly: NaOH Na+ + OH-

OH- + H+ H2O

A Solution which:A Solution which:

[H +] = [OH- ] is a neutral solution[H+ ] > [OH -] is an acidic solution[H+] < [OH -] is a basic solution

pH ScalepH Scale

[H+] [OH-] = 10-14 M2

For example:In a neutral solution [H+] = 10-7 M and [OH-] = 10-7 MWhat would make an acid, a base?

pH Scale:pH Scale:

Scale used to measure the degree of acidity. It ranges from 0 – 14

pH of 7 is neutral pH < 7 is an acidic solution pH > 7 is a basic solution Most biological fluids are within the pH range of a 6-8.

There are some exceptions such as stomach acid with the pH = 1.5

Each pH unit represents a tenfold difference (scale is logrithmic) so a slight change in pH represents a large change in actual [H+]

Buffers:Buffers:

Buffer = Substance that prevents large sudden changes in pH.

-Are combinations of H+ donor and H+ acceptor forms weak acids or bases

-Work accepting H+ ions from solution when they are in excess, and donating H+ ions to the solution when they have been depleted

Example of Buffers:Example of Buffers:

Ex. Bicarbonate Buffer response to arise in pH

H2CO3 HCO3- + H+

H+ donor response to a drop in pH H+acceptorweak acid weak base

HCl + NaHCO3 H2CO3 + NaClStrong acid weak acid

NaOH + H2CO3 NaHCO3 + H2OStrong base weak base