Should we control a Should we control a chemical that:chemical that: Causes excessive sweating and vomiting.Causes excessive sweating and vomiting. Is a major component in acid rain.Is a major component in acid rain. Can cause severe burns in its gaseous Can cause severe burns in its gaseous

state.state. Accidental inhalation can kill you.Accidental inhalation can kill you. Contributes to erosion.Contributes to erosion. Decreases the effectiveness of car brakes.Decreases the effectiveness of car brakes. Has been found in tumors of terminal Has been found in tumors of terminal

cancer patients.cancer patients.

What is the chemical?What is the chemical?

Dihydrogen monoxideDihydrogen monoxide

Otherwise known as HOtherwise known as H22OO

Chapter 2Chapter 2Water and the Water and the Fitness of the Fitness of the EnvironmentEnvironment

Three-quarters of the Earth’s surface is submerged in Three-quarters of the Earth’s surface is submerged in waterwater

The abundance of water is the main reason the Earth The abundance of water is the main reason the Earth is habitableis habitable Water is the biological medium here on EarthWater is the biological medium here on Earth All living organisms require water more than any other All living organisms require water more than any other

substancesubstance Most cells are composed of 70-95% water.Most cells are composed of 70-95% water.

Figure 3.1

Solid Liquid Gas

States of Matter

Water is a polar molecule (oxygen is more electronegative than hydrogen creating a partial negative charge on oxygen and a partial positive charge on hydrogen)

The polarity of water molecules results in unique properties. Each water molecule can form 4 hydrogen bonds. The extraordinary qualities of water are emergent properties resulting from the hydrogen bonding.

+

+

HH+

+ –

–

– –

Figure 3.2

Liquid Water Is Liquid Water Is CohesiveCohesive

Water sticks to water.Water sticks to water. Why?Why?

Because the polarity of water results Because the polarity of water results in hydrogen bonding.in hydrogen bonding.

Liquid Water is Liquid Water is AdhesiveAdhesive

Water sticks to other molecules.Water sticks to other molecules. Why? Why?

Hydrogen bonding.Hydrogen bonding.

Water transport in trees Water transport in trees uses Cohesion and uses Cohesion and

AdhesionAdhesion

CohesionCohesion Helps pull water up through the Helps pull water up through the

microscopic vessels of plantsmicroscopic vessels of plants

Water conducting cells

100 µmFigure 3.3

Water Has A Water Has A High High Surface TensionSurface Tension

The surface of water is difficult to The surface of water is difficult to stretch or break.stretch or break.

Why? Hydrogen bonding.Why? Hydrogen bonding.

Figure 3.4

Water Has A Water Has A High High Specific HeatSpecific Heat

Specific Heat - the amount of heat needed to Specific Heat - the amount of heat needed to raise 1 g of the substance 1 degree C.raise 1 g of the substance 1 degree C.

A measure of how well a substance resists A measure of how well a substance resists changing its temperature when it absorbs or changing its temperature when it absorbs or releases heat.releases heat.

Why?Why? Hydrogen bonding.Hydrogen bonding.

Heat is absorbed when hydrogen bonds breakHeat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds formHeat is released when hydrogen bonds form

TemperatureTemperature Measures the Measures the

average speed average speed of the of the molecules.molecules.

HeHeatat

Total quantity of kinetic energy due Total quantity of kinetic energy due toto

molecular motion.molecular motion.

Celsius ScaleCelsius Scale

Will be used for most of our Will be used for most of our temperature measurements.temperature measurements.

O O ooC - water freezesC - water freezes 100 100 ooC - water boilsC - water boils 37 37 ooC - human body C - human body

Water Stabilizes Water Stabilizes TemperatureTemperature

Because of its high specific heat, water can absorb and store a Because of its high specific heat, water can absorb and store a huge amount of heat from the sun.huge amount of heat from the sun.

Result - climate moderationResult - climate moderation Water stabilizes air temperatures by absorbing Water stabilizes air temperatures by absorbing heat from the Sun and from air that is warmer andheat from the Sun and from air that is warmer and releasing the stored heat to air that is cooler.releasing the stored heat to air that is cooler. Water is effective as a heat bank because it can absorb orWater is effective as a heat bank because it can absorb or release a relatively large amount of heat with only a slightrelease a relatively large amount of heat with only a slight change in its own temperature. This is the reason coastal change in its own temperature. This is the reason coastal areas generally have milder climates than inland regions.areas generally have milder climates than inland regions. Result – stabilized ocean temperatures create a favorable Result – stabilized ocean temperatures create a favorable

environment for marine lifeenvironment for marine life Result - organisms are able to survive temperature changes.Result - organisms are able to survive temperature changes.

Because organisms are made primarily of water, they Because organisms are made primarily of water, they areare

able to resist changes in their own temperatures.able to resist changes in their own temperatures.

Water Has A Water Has A High Heat High Heat Of VaporizationOf Vaporization

Heat of Vaporization: the quantity of Heat of Vaporization: the quantity of heat a liquid must absorb for 1g of it heat a liquid must absorb for 1g of it to convert to a gaseous state.to convert to a gaseous state.

Water must absorb a large amount Water must absorb a large amount of heat to break its hydrogen bonds of heat to break its hydrogen bonds from a liquid to a gas.from a liquid to a gas.

This helps to moderate This helps to moderate

Earth’s climate.Earth’s climate.

Evaporative CoolingEvaporative Cooling

Evaporative Cooling

Result:Result: As a liquid evaporates, the surface of the As a liquid evaporates, the surface of the

liquid that remains behind cools down.liquid that remains behind cools down. Contributes to the stability of temperature Contributes to the stability of temperature

in lakes and pondsin lakes and ponds Provides a mechanism that prevents Provides a mechanism that prevents

terrestrial organisms from overheating EX. terrestrial organisms from overheating EX. sweating sweating

Why?Why? Hydrogen bondingHydrogen bonding

Water Expands When It Water Expands When It FreezesFreezes

The distance between water molecules The distance between water molecules INCREASESINCREASES from the liquid to the solid from the liquid to the solid form.form.

Why?Why? Hydrogen bondingHydrogen bonding Hydrogen bonds keep the water Hydrogen bonds keep the water

molecules far enough apart that they lock molecules far enough apart that they lock into a crystalline lattice structure, making into a crystalline lattice structure, making ice about 10% less dense than water at 4 ice about 10% less dense than water at 4 degrees Celsius.degrees Celsius.

Solids and LiquidsSolids and Liquids

Water Benzene

Floats Sinks

ResultResult Floating ice insulates the liquid water Floating ice insulates the liquid water

below, preventing it from freezing below, preventing it from freezing and allowing aquatic life to live under and allowing aquatic life to live under the frozen surface.the frozen surface.

Liquid water

Hydrogen bonds constantly break and re-form

Ice

Hydrogen bonds are stable

Hydrogen bond

Figure 3.5

Water Is The Water Is The Universal Universal SolventSolvent

Water will form a solution with many Water will form a solution with many materials.materials.

Why?Why? Hydrogen bondingHydrogen bonding

Water is polar (unequal sharing of electrons)Water is polar (unequal sharing of electrons)ionic substances are soluble in waterionic substances are soluble in waterpolar dissolves polar ( sugar in water)polar dissolves polar ( sugar in water)

Nonpolar substances do not dissolve in waterNonpolar substances do not dissolve in waterEX. lipidsEX. lipids

SolutionSolutionHomogeneous mixture of two or more Homogeneous mixture of two or more

substances.substances.

SolventSolvent

The dissolving agent.The dissolving agent.

The material in the The material in the greater quantity.greater quantity.

SoluteSoluteThe substance that The substance that is dissolved.is dissolved.

The material in The material in the lesser the lesser

quantity.quantity.

Hydrophilic MaterialsHydrophilic Materials

Materials that dissolve in water.Materials that dissolve in water. HydroHydro - water - water philicphilic - to like or love - to like or love Have ionic or polar regions (polar Have ionic or polar regions (polar

covalent bonds) on their molecules covalent bonds) on their molecules for Hfor H++ bonds. bonds.

HydrophobicHydrophobic

Materials that repel water.Materials that repel water. HydroHydro - water - water phobicphobic - to fear - to fear Have non-polar covalent bonds. Ex - Have non-polar covalent bonds. Ex -

lipids.lipids.

Without Water Without Water Life Would Not Life Would Not Be Possible!!Be Possible!!

Solution ConcentrationSolution Concentration

Usually based on Molarity.Usually based on Molarity. Molarity - the number of moles of solute per Molarity - the number of moles of solute per

liter of solution.liter of solution.

MolesMoles

The molecular weight of a substance in grams.The molecular weight of a substance in grams. A mole of one substance has exactly the same A mole of one substance has exactly the same

number of molecules as a mole of another number of molecules as a mole of another substance.substance.

Avogadro’s number is the number of Avogadro’s number is the number of molecules in a mole. molecules in a mole.

6.02 X 106.02 X 102323

One Mole of eachOne Mole of each

Sulfur

Sugar

Copper Sulfate

Mercury Oxide

Copper

Sodium Chloride

Dissociation of WaterDissociation of Water Water can sometimes split into two ions.Water can sometimes split into two ions.

In pure water the concentration of each In pure water the concentration of each

ion is 10ion is 10-7-7

Adding certain solutes disrupts the balance Adding certain solutes disrupts the balance between the two ions.between the two ions.

The two ions are very reactive and can The two ions are very reactive and can drastically affect a cell.drastically affect a cell.

AcidsAcids

Materials that can release HMaterials that can release H++

increases the hydrogen ion concentration of a increases the hydrogen ion concentration of a solutionsolution

Example: HClExample: HCl

HCl HHCl H++ + Cl + Cl--

Acid RainAcid Rain

Acid RainAcid Rain

BasesBases

Materials that can absorb HMaterials that can absorb H++

Often reduce HOften reduce H+ + by producing OHby producing OH- -

Example: NaOHExample: NaOH

NaOH NaNaOH Na++ + OH + OH- -

pH ScalepH Scale

A logarithmic scale for showing HA logarithmic scale for showing H++ concentrationconcentration

pH = - log [HpH = - log [H++]]

pH ScalepH Scale

Example:Example:

For a neutral solution:For a neutral solution:

[H[H++] is 10] is 10-7-7

or - log 10or - log 10-7-7

or - (-7)or - (-7)

or 7or 7

Acids: pH <7 etc.Acids: pH <7 etc. Bases: pH >7 etc.Bases: pH >7 etc. Each pH unit is a Each pH unit is a 10x10x change in H change in H++

CommentComment

[H[H++] + [OH] + [OH--] = 14] = 14 Therefore, if you know the Therefore, if you know the

concentration of one ion, you can concentration of one ion, you can easily calculate the other.easily calculate the other.

BuffersBuffers

The internal pH of most living cellsThe internal pH of most living cells Must remain close to pH 7Must remain close to pH 7

BuffersBuffers

Materials that have both acid and base Materials that have both acid and base properties.properties.

Resist pH shifts.Resist pH shifts. Cells and other biological solutions often Cells and other biological solutions often

contain buffers to prevent damage.contain buffers to prevent damage.

BuffersBuffers Are substances that minimize changes in the Are substances that minimize changes in the

concentrations of hydrogen and hydroxide ions in concentrations of hydrogen and hydroxide ions in a solutiona solution

Consist of an acid-base pair that reversibly Consist of an acid-base pair that reversibly combines with hydrogen ionscombines with hydrogen ions

The Threat of Acid The Threat of Acid PrecipitationPrecipitation

Acid precipitationAcid precipitation Refers to rain, snow, or fog with a pH lower than Refers to rain, snow, or fog with a pH lower than

pH 5.6pH 5.6 Is caused primarily by the mixing of different Is caused primarily by the mixing of different

pollutants with water in the airpollutants with water in the air Caused primarily by the presence in the Caused primarily by the presence in the

atmosphere of sulfur oxides and nitrogen oxides, atmosphere of sulfur oxides and nitrogen oxides, created by the burning of fossil fuelscreated by the burning of fossil fuels

Acid precipitationAcid precipitation Can damage life in Earth’s ecosystemsCan damage life in Earth’s ecosystems

0

12

34

56

78

910

1112

1314

Moreacidic

Acidrain

Normalrain

Morebasic

Figure 3.9