Unit 2:Unit 2: All Biology is ChemistryAll Biology is Chemistry

Water & SolutionsWater & Solutions

ObjectivesObjectives

At the conclusion of this lesson students will be able At the conclusion of this lesson students will be able to:to:

1.1. describe the structure of a water moleculedescribe the structure of a water molecule

2.2. explain what is meant by a molecule’s explain what is meant by a molecule’s polaritypolarity

3.3. explain why explain why hydrogen bonds hydrogen bonds form between water form between water moleculesmolecules

4.4. identify common properties of water that result from identify common properties of water that result from hydrogen bondinghydrogen bonding

5.5. identify the difference between identify the difference between solutessolutes and and solventssolvents in in solutionssolutions

6.6. differentiate between differentiate between acidsacids and and basesbases

7.7. understand how to read and interpret the understand how to read and interpret the pH scalepH scale

8.8. define a define a bufferbuffer and explain their role in living systems and explain their role in living systems

The Structure of WaterThe Structure of Water

Composed of two hydrogen atoms Composed of two hydrogen atoms covalently bonded to an oxygen atom.covalently bonded to an oxygen atom.

Hydrogen

Hydrogen

Hydro

gen

Hydro

gen

OxygenOxygen

PolarityPolarity

However, oxygen and However, oxygen and hydrogen do not share hydrogen do not share electrons equally.electrons equally. As a result…As a result…

• Oxygen atom has a partial Oxygen atom has a partial negative charge (negative charge (δδ-) -)

• Hydrogen atoms have Hydrogen atoms have partial positive charges partial positive charges ((δδ+)+)

• Total charge of the water Total charge of the water molecule is still neutralmolecule is still neutral

1 p1 p

1 p

1 p

Oxygen8 p8 n

Oxygen8 p8 n

δδ--

δδ++δδ++

Obj. 1Obj. 1

Space filling model of a water molecule

Hydrogen BondingHydrogen Bonding

Water molecules have an uneven Water molecules have an uneven distribution of chargedistribution of charge Positively charged region (Positively charged region (δδ++) of one ) of one

water molecule is attracted to the water molecule is attracted to the negatively charged region (negatively charged region (δδ--) of a ) of a nearby water molecule.nearby water molecule.

This attraction is called a This attraction is called a hydrogen hydrogen bond.bond.

H H

H

H

OOδδ--δδ-- δδ++δδ++

δδ++δδ++H H

H HOO

δδ--δδ-- δδ++δδ++

δδ++δδ++

Hydrogen BondsHydrogen Bonds

Weak forces of attractionWeak forces of attraction Form, break, and reform frequentlyForm, break, and reform frequently Number of hydrogen bonds in water Number of hydrogen bonds in water

depends on its state (solid, liquid, or gas)depends on its state (solid, liquid, or gas)

Significance of Hydrogen Significance of Hydrogen BondsBonds

Account for the unique properties of Account for the unique properties of waterwater CohesionCohesion Surface tensionSurface tension AdhesionAdhesion Ability to absorb a relatively large amount Ability to absorb a relatively large amount

of heat energyof heat energy Ability to cool surfaces through evaporationAbility to cool surfaces through evaporation Solid state is less dense than its liquid stateSolid state is less dense than its liquid state Ability to dissolve many substancesAbility to dissolve many substances

Obj. 2Obj. 2

CohesionCohesion

CohesionCohesion - an attractive force that - an attractive force that holds molecules of a single holds molecules of a single substance togethersubstance together

Surface tensionSurface tension

Tendency of water molecules on the Tendency of water molecules on the edges of a water droplet to attract edges of a water droplet to attract inward toward other water molecules inward toward other water molecules thus producing a “skin”thus producing a “skin”

AdhesionAdhesion

AdhesionAdhesion – attractive force between – attractive force between two particles of different substancestwo particles of different substances

Temperature ModerationTemperature Moderation

TemperatureTemperature is a is a measure of measure of heatheat which is which is a form of a form of energyenergy Water can absorb large Water can absorb large

amounts of energy as heat amounts of energy as heat for its molecular sizefor its molecular size

Water has the highest Water has the highest specific heat specific heat of any of any common substance.common substance.Specific heat Specific heat is the heat required to raise the temperature of one gram of a is the heat required to raise the temperature of one gram of a

substance one degree Celsius.substance one degree Celsius.

Effects of a High Specific Effects of a High Specific HeatHeat

Water can absorb/release a large Water can absorb/release a large quantity of heat without a large quantity of heat without a large change in temperaturechange in temperature•Moderates Moderates coastal climatescoastal climates

•Reduces Reduces dramatic day-dramatic day-night night temperature temperature fluctuationsfluctuations

Evaporative CoolingEvaporative Cooling

As water As water evaporates, the evaporates, the surface of the surface of the water that remains water that remains behind cools.behind cools.

Principle behind Principle behind sweating to sweating to maintain body maintain body temperature in temperature in land animalsland animals

Density of IceDensity of Ice Angle of hydrogen Angle of hydrogen

bonds causes ice bonds causes ice crystals to have lots of crystals to have lots of open spaceopen space

Open space leads to low Open space leads to low densitydensity

As a result, ice floats!As a result, ice floats! Ponds & lakes freeze Ponds & lakes freeze

from top to bottom.from top to bottom. Ice insulates deeper Ice insulates deeper

water from colder air.water from colder air.

Ice crystalIce crystal

Liquid waterLiquid water

MixturesMixtures two or more substances which are combined so two or more substances which are combined so

that each substance keeps its own chemical that each substance keeps its own chemical identity.identity. Water combines to form many types of mixturesWater combines to form many types of mixtures

Mixtures can be classified as Mixtures can be classified as HomogeneousHomogeneous – a combination of substances – a combination of substances

that is uniform throughoutthat is uniform throughout

or or Heterogeneous Heterogeneous – a combination of substances – a combination of substances

that are physically distinct from one anotherthat are physically distinct from one another

Types of MixturesTypes of Mixtures

Solution Colloid Suspension

Homogeneous Homogeneous Heterogeneous

Dissolved particles (solute) will remain mixed indefinitely in another substance (solvent).

Dispersed particles will remain mixed indefinitely.

Suspended particles will separate spontaneously.

No Tyndall effect Tyndall effect – light beam is scattered.

May or may not show Tyndall effect

Cannot be filtered Cannot be filtered Particles can be separated by filtration.

Examples: seawater, brass, air

Examples: butter, smoke, fog, ink, paint

Examples: sand and water, concrete

Homogeneous MixturesHomogeneous Mixtures

SolutionSolution – A mixture in which one – A mixture in which one substance (the substance (the solutesolute) is dissolved ) is dissolved completely into another substance completely into another substance (the (the solventsolvent) so that the two cannot ) so that the two cannot be distinguishedbe distinguished

Water is the Water is the universal solventuniversal solvent Examples:Examples:

Salt in waterSalt in water Powdered drink mix in waterPowdered drink mix in water SalivaSaliva

Heterogeneous MixturesHeterogeneous Mixtures

SuspensionSuspension – heterogeneous – heterogeneous mixture that contains fine solids mixture that contains fine solids or liquids that will settle out or liquids that will settle out spontaneouslyspontaneously Example: sand in waterExample: sand in water

ColloidColloid – heterogeneous mixture – heterogeneous mixture containing particles larger than containing particles larger than solutes, but small enough to not solutes, but small enough to not settle out spontaneouslysettle out spontaneously Examples: blood, fog, smoke, butter, Examples: blood, fog, smoke, butter,

paint, inkpaint, ink

GlossaryGlossary adhesion adhesion – an attractive force between two – an attractive force between two

particles of different substancesparticles of different substances cohesion cohesion – an attractive force that holds – an attractive force that holds

molecules of a single substance togethermolecules of a single substance together hydrogen bond hydrogen bond – force of attraction between – force of attraction between

a hydrogen molecule with a partial positive a hydrogen molecule with a partial positive charge and another atom or molecule with a charge and another atom or molecule with a partial or full negative chargepartial or full negative charge

polar compoundpolar compound – a compound with an – a compound with an uneven distribution of charge within the uneven distribution of charge within the moleculemolecule

Work CitedWork Cited "Graduated cylinders." "Graduated cylinders." 10 mL graduated cylinder10 mL graduated cylinder. 1995-1995. NT Curriculum Project, . 1995-1995. NT Curriculum Project,

UW- UW- Madison. 19 Oct 2006 <www.uwplatt.edu/.../volume/gradcyl/gradcyl.htm>. Madison. 19 Oct 2006 <www.uwplatt.edu/.../volume/gradcyl/gradcyl.htm>. Lower, Stephen. "HLower, Stephen. "H22O: a gentle introduction to the structure of water." 16 May 2005. O: a gentle introduction to the structure of water." 16 May 2005.

Dept of Dept of Chemistry, Simon Fraser University. 19 Oct Chemistry, Simon Fraser University. 19 Oct 2006<http://www.chem1.com/acad/sci/aboutwater.html>. 2006<http://www.chem1.com/acad/sci/aboutwater.html>.

Microsoft Corporation, "Hydrogen Bonding in Water." MSN Encarta. 19 Oct 2006 Microsoft Corporation, "Hydrogen Bonding in Water." MSN Encarta. 19 Oct 2006 <http://encarta.msn.com/media_461547672_761563983_-<http://encarta.msn.com/media_461547672_761563983_-1_1/Hydrogen_Bonding_in_Water.html>.1_1/Hydrogen_Bonding_in_Water.html>.

““Mixture” Mixture” About.com Chemistry.About.com Chemistry. 2009. 23 Oct 2009 2009. 23 Oct 2009 <http://chemistry.about.com/od/dictionariesglossaries/g/defmixture.htm>. <http://chemistry.about.com/od/dictionariesglossaries/g/defmixture.htm>. Nave, R. "Water." Hyperphysics Chemistry. 19 Oct 2006 <hyperphysics.phy-Nave, R. "Water." Hyperphysics Chemistry. 19 Oct 2006 <hyperphysics.phy-

astr.gsu.edu/.../water.html>. astr.gsu.edu/.../water.html>. Saloutos, Peter. "Surface Tension in Water Droplets." MSN Encarta. 19 Oct 2006 Saloutos, Peter. "Surface Tension in Water Droplets." MSN Encarta. 19 Oct 2006

<http://encarta.msn.com/media_461560536_761563983_-<http://encarta.msn.com/media_461560536_761563983_-1_1/Surface_Tension_in_Water_Droplets.html>. 1_1/Surface_Tension_in_Water_Droplets.html>.

"Specific Heat." 1999. 19 Oct 2006 "Specific Heat." 1999. 19 Oct 2006 <www.chem.uiuc.edu/webFunChem/heat/heat.htm>.<www.chem.uiuc.edu/webFunChem/heat/heat.htm>.

"Sunset Island Wedding." "Sunset Island Wedding." Miami SkylineMiami Skyline. 31 Aug 2006. 19 Oct 2006 . 31 Aug 2006. 19 Oct 2006

<www.weddingsbythesea.net/sunset.htm>.<www.weddingsbythesea.net/sunset.htm>. ““Surface tension” Molecules. Retrieved on 19 Oct. 2006 from <http://universe-Surface tension” Molecules. Retrieved on 19 Oct. 2006 from <http://universe-

review.ca/option2.htm>. review.ca/option2.htm>.

DrillDrill19 October 200919 October 2009

K-W-LK-W-L With a partner, complete the first two With a partner, complete the first two

columns of the chart:columns of the chart:

What do I What do I KNOWKNOW about about waterwater

What do I What do I WANTWANT to to know about know about waterwater

What have I What have I LEARNEDLEARNED about waterabout water