Water Walk• 10 Different pictures/scenarios with brief

description• Write Down Number of Station and the scenario

you are looking at. – Start at the number of the station you are at– Move clockwise

• Answer the following questions for each…a) How does the structure of water relate to this

action/scenario?

WaterThe Universal Solvent

A little bit about water• Water is the biological medium on Earth

– Universal Solvent– Solvent: the substance that the solute (salt) is dissovled in

(water)– Solute: substance (salt) that is dissolved in a liquid– Solution: when solutes are uniformly distributed throughout a

water solvent

• All living organisms require water more than any other substance

• Most cells are surrounded by water, and cells themselves are about 70-95% water

• The abundance of water is the main reason the Earth is habitable

Water• Chemical Formula

• H2O• How water is formed

• Covalent compound• Which atom has a stronger pull for electrons?

• The one that is bigger…oxygen• Electrons are shared but they spend more time around Oxygen

atom than the hydrogen atoms• This makes water a…

• Polar Molecule• Uneven sharing of electrons• slight positive charge by hydrogens• Slight negative charge by oxygen• POLARITY• What do opposites do?

• Water molecules are attracted to other water molecules to form HYDROGEN BONDS• Weak attraction between hydrogen atom of one molecule

and an oxygen, nitrogen or sulfur bond of another molecule.

LE 3-2

Properties of water

• Versatility as a solvent• Cohesive and Adhesive behavior• Expansion upon freezing• Temperature moderation

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• Water is a versatile solvent due to its polarity• An aqueous solution is one in which water is the

solvent

Mixture, Solutions and Suspensions…oh my!

• Mixtures– physically, not chemically mixed compounds– Not necessarily evenly distributed– Homogenous

• Evenly distributed• Cannot see the different parts

– Heterogenous• Not uniformly distributed• you can see the parts

• Solution– Homogenous Mixture

• components are uniformly distributed

– Solutes and solvents– Ex. Salt water

• Suspension– Mixture of water and non-dissolved material– Some of the most biologically important substances are both solutions and

suspensions• Ex. blood

Water as the Universal Solvent

• Water is an effective solvent because it readily forms hydrogen bonds

• When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell

• Water can also dissolve compounds made of nonionic polar molecules

• Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions

LE 3-6

Na+

Na+

Cl–Cl–

+

+

+

+

+

+

++

–

–

–

–

–

–

–

–

–

–

–

LE 3-7a

Lysozyme moleculein a nonaqueous environment.

LE 3-7b

Lysozyme molecule in a aqueous environment.

• Transpiration:– Evaporation of water through the leaves of plants

• “stomata” are the tiny pores in the leaves of plants through which water (and oxygen) escapes…carbon dioxide enters here…

• Cohesive and Adhesive behavior• Cohesion: when similar molecules stick together

(droplet of water)• hydrogen bonds hold water molecules together• Cohesion helps the transport of water against gravity in

plants

• Adhesion: when unlike molecules stick together (water on glass)

• Adhesion of water to plant cell walls also helps to counter gravity

• How does water get from roots to the leaves of a tall tree?

Capillary Action• DEF: The movement of

water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension

• Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules.

Capillary Action

• Think of what happens when you dip a paper towel in water

• What happens when you put celery in colored water

Cohesion accounts for SURFACE TENSION

• Surface tension is a measure of how hard it is to break the surface of a liquid

Heat and Temperature• Kinetic energy is the energy of motion• Heat is a measure of the total amount of kinetic energy

due to molecular motion• Temperature measures the intensity of heat due to the

average kinetic energy of molecules

Expansion Upon Freezing• Liquid H2O WATER!

– Molecules of a liquid move how?• Slide past each other!• Hydrogen bonds between water molecules keep breaking

and reforming

• Solid H2OICE!– Hydrogen bonds become stuck on whatever nearby

water molecule they are attached to– Now molecules cannot slide past each other…

therefore, they CANNOT pack densely together– Liquid water is more dense, therefore…– ICE FLOATS!!!

What Happens When Hydrogen Bonds Form

Between Water Molecules?• ENERGY is Released!!!

– Energy=HEAT• So…when water freezes,

is energy released or absorbed?

• RELEASED! • When water freezes, its

warms up its surroundings.

What Happens When Hydrogen Bonds Between Water Molecules

Break???• This REQUIRES ENERGY!!!• Energy or HEAT MUST Be

absorbed• To break hydrogen bonds,

you just need to add heat…

Moderation of Temperature• Water absorbs heat from warmer air and releases

stored heat to cooler air• Water can absorb or release a large amount of heat

with only a slight change in its own temperature

Weather and Water

• Coastal Areas– During the hot day, the ocean/lake will absorb

energy from the air so that it feels cooler– At night, when the air is cooler, the water releases

all the stored energy, making it warmer at night– “moderate” temperature

• Inland areas (no water nearby)– During the hot day, there is NO water to absorb

heat so it is realllllyy hot (think desert)– At night, no energy is release, so it gets very cold

Water’s High Specific Heat• The specific heat of a substance is the amount of heat

that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC

• Water’s high specific heat minimizes temperature fluctuations to within limits that permit life– Heat is absorbed when hydrogen bonds break– Heat is released when hydrogen bonds form

Evaporative Cooling

• Evaporation is transformation of a substance from liquid to gas• Heat of vaporization is the heat a liquid must absorb for 1 gram to be converted to

gas• As a liquid evaporates, its remaining surface cools, a process called evaporative

cooling • Evaporative cooling of water helps stabilize temperatures in organisms and bodies

of water• “Sweating” liquid to gas requires heat…this heat comes from inside our body• What does the saying “It’s not the heat, it’s the humidity” mean?• Humidity: water vapor in the air• If there is more water in the air, it is harder for water molecules to evaporate off

your skin…so how do you feel?– Hot and sticky!

Surfactants• A “surface acting” agent• a compound which lowers the

surface tension of a liquid, increasing the contact between the liquid and another substance

• Surfactants have a hydrophobic tail attracted to NON-POLAR molecules and a Hydrophilic tail, which is POLAR and attracted to polar molecules (such as…WATER!)

• There are a wide variety of surfactants, which work with oil, water, and an assortment of other liquids

Types of Attractions• Covalent• Ionic• Hydrogen• Van der Waals Forces

– Intermolecular force of attraction– Due to uneven sharing of electrons in covalent bonds– Slight attraction between oppositely charged regions of molecules that are closely packed

together– Holds large molecules together

Hydrophilic and Hydrophobic Substances

• A hydrophilic substance is one that has an affinity (likes!) for water

• A hydrophobic substance is one that does not have an affinity (does NOT like; scared of) for water

How water acts in solution• Occasionally a water molecule

dissociates (breaks up) into ions H2O H+ + OH-This happens to every one water

molecule in a million in pure water…not very common

– The H+ immediately reacts with another water molecule in the solution to make a HYDRONIUM ion H30+

Acids and Bases

• What do you know?

Acids• An acid is any substance that increases

the H+ concentration of a solution– ADDS H+ ions to water– taste sour – turn cabbage juice red – turn blue litmus paper red

• Strong acids (LOW pH)– Dissociate completely in water– Adds LOTS of H+ ions– Hydrochloric acid HCl– HCl H+ and Cl-

• Weak Acids (pH slightly below 7)– Partially dissociate in water– Only add a little bit of H+ ions– Coffee, tomato juice, acetic acid

  H         O        |       //H--C—C        |       \\       H         O-

CH3COOH = CH3COO- + H+

Bases• A base is any substance that reduces the H+ concentration of a

solution• ADDS HYDROXIDE ions (OH-) to water

– OH- ions bind to any free H+ ions to make…a molecule of water– This does what to the concentration of H+ ions ion the water?\

• DECREASE H+ ion concentration, therefore, making it basic• Characteristics:

– taste bitter – feels slimy – turns cabbage juice yellow, green or blue depending upon the solution

concentration – turns red litmus paper blue

• Strong Bases (pH High- close to 14)– Completely dissociate in solution– Adds LOTS of OH- ion to solutions– NaOH sodium hydroxide NaOH Na+ and OH-

• Weak Bases– Partially dissociate in water – Adds only a few OH- to solution– Ammonia NH3

Strong Acids and Bases

HCl - hydrochloric acid HNO3 - nitric acid H2SO4 - sulfuric acid HBr - hydrobromic acid HI - hydroiodic acid HClO4 - perchloric acid

LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide RbOH - rubidium hydroxide CsOH - cesium hydroxide

DISSOCIATE COMPLETELYWhat do you notice?

The pH Scale

• The pH of a solution is determined by the relative concentration of hydrogen ions H+– So it is really measuring how acidic something is– formula is..– pH=-log[H+]

• Negative means opposite, this is why a low pH has MORE H+ ions

• [x] means concentration

• Acidic solutions have pH values less than 7– More H+ ions

• Basic solutions have pH values greater than 7– More OH- ions, less H+ ions

• Most biological fluids have pH values in the range of 6 to 8

LE 3-8pH Scale

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14Oven cleaner

Household bleach

Household ammonia

Milk of magnesia

Seawater

Pure waterHuman blood

UrineRainwater

Black coffee

Tomato juice

Vinegar, beer, wine,cola

Digestive (stomach)juice, lemon juice

Battery acid

Neutral[H+] = [OH–]

Inc

rea

sin

gly

Ac

idic

[H+]

> [

OH

–]

Inc

rea

sin

gly

Ba

sic

[H+]

< [

OH

–]

Buffers

• The internal pH of most living cells must remain close to pH 7

• Buffers are substances that minimize changes in concentrations of H+ and OH- in a solution– Weak acids are a buffer for strong bases– Weak bases are a buffer for strong acids

• Most buffers consist of an acid-base pair that reversibly combines with H+

Acids and Bases in the Living Things

• Changes in concentrations of H+ and OH- can drastically affect the chemistry of a cell

• When you breath…• CO2 + H2O H⇌ + + HCO-

3 • Carbon dioixde water hydrogen ion bicarbonate ion

The Threat of Acid Precipitation• Acid precipitation refers to

rain, snow, or fog with a pH lower than 5.6

• Acid precipitation is caused mainly by the mixing of different pollutants with water in the air

• Acid precipitation can damage life in lakes and streams

• Effects of acid precipitation on soil chemistry are contributing to the decline of some forests

LE 3-9

0123456789

1011121314

Morebasic

Normalrain

Moreacidic

Acidrain

Hydrophilic and Hydrophobic Substances

• A hydrophilic substance is one that has an affinity (likes!) for water

• A hydrophobic substance is one that does not have an affinity (does NOT like; scared of) for water

Law of Conservation of Energy and Matter

• Energy and Matter cannot be created or destroyed, only change form

• All atoms on one side of the equation must be accounted for on the other side of the equation

• All chemical formulas MUST balance.

• C6H12O6 + O2------> CO2 + H2O• Count atoms of each element on each side.• Is it balanced (does it follow law of conservation of matter?)• Increase number of molecules of each compound to balance.• Change COEFFICENT

– Coefficient is the number before the compound (only number you can change)

• C6H12O6 + 6O2------> 6CO2 + 6H2O• (glucose) + (oxygen)-------(carbon dioxide) + (water)

– 6 carbons on the left 6 carbons on the right– 12 hydrogen on the left 12 hydrogen on the right– 18 oxygen on the left 18 oxygen on the right

•