Water and Its Water and Its PropertiesProperties

Honors BiologyHonors BiologyMs. KimMs. Kim

Water: Molecule That Water: Molecule That Supports All of LifeSupports All of Life

•Water is the biological medium Water is the biological medium here on Earthhere on Earth–Provides an environment Provides an environment where metabolic rxns can where metabolic rxns can happenhappen

–HH220 is often a product or 0 is often a product or reactant in biological rxnsreactant in biological rxns

–All living organisms require All living organisms require water more than any other water more than any other substance (cells ~80%Hsubstance (cells ~80%H220 ) 0 )

•¾ of the Earth’s surface is ¾ of the Earth’s surface is submerged in watersubmerged in water

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

Figure 3.1

• The water molecule is a The water molecule is a polarpolar moleculemolecule

• The polarity of water moleculesThe polarity of water molecules– Allows it form hydrogen bonds with Allows it form hydrogen bonds with

each othereach other– Contributes to the various properties Contributes to the various properties

water exhibitswater exhibits

+

+

H

H+

+

–

–

– –

Oxygen has a Oxygen has a greater “pull” on greater “pull” on

e-’s than e-’s than hydrogenhydrogen forms forms

partial – and partial partial – and partial + end of molecule+ end of molecule

((dipoledipole nature) nature)

What is “polarity”?What is “polarity”? • A molecule that has different A molecule that has different

charges on each end or “pole” charges on each end or “pole”

• Asymmetrical ends = polarAsymmetrical ends = polar

• Water polarity allows for H-bonding Water polarity allows for H-bonding (strong hydrogen attractions)(strong hydrogen attractions)

Polar and Nonpolar Polar and Nonpolar MoleculesMolecules

• Polar MoleculePolar Molecule –– Unequal distribution of Unequal distribution of chargescharges– One side is more positive One side is more positive – One side is more negative One side is more negative – Dissolve in waterDissolve in water– Ex: WaterEx: Water

• Nonpolar Molecule Nonpolar Molecule – no separation of charge, so – no separation of charge, so no positive or negative poles are formed. no positive or negative poles are formed. – Do not dissolve in waterDo not dissolve in water– Ex: CO2, O2, lipidsEx: CO2, O2, lipids Think of the interaction of

two magnets and how they either are attracted to each

other or repel.

How do water molecules How do water molecules interact with each other?interact with each other?

• Polar water molecules can be Polar water molecules can be attracted to each otherattracted to each other

• The hydrogen atom with its’ partial The hydrogen atom with its’ partial positive charge (+) is attracted to positive charge (+) is attracted to the oxygen atom (partial negative the oxygen atom (partial negative charge) of a charge) of a differentdifferent water water molecule!molecule!

– This is known as a This is known as a hydrogen bondhydrogen bond

Hydrogen BondsHydrogen Bonds

• Bonding between Bonding between moleculesmolecules

• Very weak, but very important Very weak, but very important for for the various the various

characteristics of characteristics of of water…of water…

Polar covalent bondsPolar covalent bonds

Polar StructurePolar Structure

5 Characteristics of 5 Characteristics of WaterWater

1. Cohesion1. Cohesion

2. Adhesion2. Adhesion

3. High Specific Heat3. High Specific Heat

4. Less Dense as a Solid4. Less Dense as a Solid

5. Water is a terrific solvent5. Water is a terrific solvent

Water PropertiesWater Properties**H-bonding is responsible for these **H-bonding is responsible for these

propertiesproperties1. 1. Cohesion Cohesion (“co-” means “together”)(“co-” means “together”)

– Tendency of molecules of the Tendency of molecules of the SAMESAME “kind” to “kind” to stick togetherstick together

– Partial - & partial + ends attract each otherPartial - & partial + ends attract each other

•Examples: water “sticking” to itself, Examples: water “sticking” to itself, transpirational-pull, surface tensiontranspirational-pull, surface tension

2. Surface Tension: 2. Surface Tension: – Measure of how difficult it is to stretch or Measure of how difficult it is to stretch or

break the surface of a liquid/ resist an break the surface of a liquid/ resist an external force.external force.• HH22O has high surface tension O has high surface tension

• Due to H-bondsDue to H-bonds

Water “Water “stickssticks” to itself” to itself

•Surface tension Surface tension –another type of cohesionanother type of cohesion

– a measure of how hard it is to break a measure of how hard it is to break the surface of a liquidthe surface of a liquid

– Water molecules form a “barrier” by Water molecules form a “barrier” by H-bonding togetherH-bonding together

– Water does NOT pull apart very easily Water does NOT pull apart very easily acts like elastic acts like elastic

Surface TensionSurface Tension

2. Adhesion 2. Adhesion

• The type of attraction that happens between two The type of attraction that happens between two differentdifferent molecules molecules

• Partial - & partial + ends of water attract to ends of Partial - & partial + ends of water attract to ends of other moleculesother molecules

• Water will make hydrogen bonds with other surfaces Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cottonsuch as glass, soil, plant tissues, and cotton

• Adhesion forms stronger bonds than cohesionAdhesion forms stronger bonds than cohesion• Examples: water “sticking” to stuff (i.e.-towels, Examples: water “sticking” to stuff (i.e.-towels,

clothes, paper, glass) clothes, paper, glass)

• More Examples: More Examples: – Meniscus forming on graduated Meniscus forming on graduated cylinder! cylinder! – TranspirationTranspiration - plants and - plants and

trees remove water from the soiltrees remove water from the soil– Paper towels soaking up waterPaper towels soaking up water

•Cohesion & Adhesion Acting Cohesion & Adhesion Acting TogetherTogether– Helps pull water up through the Helps pull water up through the

microscopic vessels of plants is microscopic vessels of plants is Called Called capillary actioncapillary action

Another Example of Another Example of Cohesion and Adhesion…Cohesion and Adhesion…

CohesionAdhesion

3. Water has a High 3. Water has a High Specific HeatSpecific Heat

• specific heatspecific heat = amount of heat that must = amount of heat that must be absorbed or lost for 1 gram of be absorbed or lost for 1 gram of substance to change its temp. by 1ºCsubstance to change its temp. by 1ºC

• Water has a high specific heat, meaning it resists Water has a high specific heat, meaning it resists temperature change! temperature change! – Because of the hydrogen bonds between water molecules Because of the hydrogen bonds between water molecules

• Water has to absorb more heat energy to increase Water has to absorb more heat energy to increase overall temperature compared to other overall temperature compared to other compoundscompounds– Ex: Lake Michigan is really cold until ~ August…it takes a long Ex: Lake Michigan is really cold until ~ August…it takes a long

time to warm up!!time to warm up!!

• Helps to regulate cell temperatures in organismsHelps to regulate cell temperatures in organisms

•Water has a Water has a high specific high specific heat heat so its temperature so its temperature does NOT fluctuate very does NOT fluctuate very much much allows life to live allows life to live in waterin water–moderate Earth's moderate Earth's climate by climate by buffering large fluctuations buffering large fluctuations in temperature.in temperature.

How come

icebergs float?

4. Low Density in Solid 4. Low Density in Solid FormForm

•Allows for insulation of bodies Allows for insulation of bodies of water by floating iceof water by floating ice

•Solid water (i.e.-ice)Solid water (i.e.-ice)– Is less dense than liquid waterIs less dense than liquid water– Floats in liquid waterFloats in liquid water

•Since ice floats in water Since ice floats in water – Life can exist under frozen Life can exist under frozen

surfaces of lakes/polar seassurfaces of lakes/polar seas

• Ice floats because ice is Ice floats because ice is lessless dense than dense than liquid water! liquid water! – This is because the H bonds hold the water This is because the H bonds hold the water

molecules farther apart than in liquid watermolecules farther apart than in liquid water

•The hydrogen bonds in iceThe hydrogen bonds in ice– Are more “ordered” than in Are more “ordered” than in liquid water, making ice less liquid water, making ice less densedense

Liquid water

Hydrogen bonds Hydrogen bonds constantly break and re-formconstantly break and re-form

IceIceHydrogen bonds are Hydrogen bonds are

stablestable

5. The Solvent of Life5. The Solvent of Life Water is a great solvent (Water is the Water is a great solvent (Water is the

universal solvent)universal solvent) SoluteSolute –– gets dissolved (Hot Cocoa mix) gets dissolved (Hot Cocoa mix) SolventSolvent –– does the dissolving (Water) does the dissolving (Water) SolutionSolution –– uniform mixture of two or more uniform mixture of two or more

substances substances

• SolutionSolution = a UNIFORM = a UNIFORM mixture of 2+ mixture of 2+ substances substances – LOOK the same LOOK the same

(uniform) throughout(uniform) throughout• SolSolvventent = substance = substance

that is doing the that is doing the dissolvingdissolving– The “dissolThe “dissolvver” er”

• SoluteSolute = substance(s) = substance(s) getting dissolvedgetting dissolvedEx:Ex: salt water solution

Why is water a good Why is water a good solvent?solvent?• Water is called the Water is called the universal solventuniversal solvent because more  because more

substances dissolve in water than in any other chemical. substances dissolve in water than in any other chemical.

• This has to do with the polarity of each water molecule. This has to do with the polarity of each water molecule. The hydrogen side of each water (HThe hydrogen side of each water (H22O) molecule carries O) molecule carries a slight positive electric charge, while the oxygen side a slight positive electric charge, while the oxygen side carries a slight negative electric charge. carries a slight negative electric charge.

• This helps water dissociate ionic compounds into their This helps water dissociate ionic compounds into their positive and negative ions. The positive part of an ionic positive and negative ions. The positive part of an ionic compound is attracted to the oxygen side of water while compound is attracted to the oxygen side of water while the negative portion of the compound is attracted to the the negative portion of the compound is attracted to the hydrogen side of water.hydrogen side of water.

• Despite its name as the "universal solvent" there are Despite its name as the "universal solvent" there are many compounds water won't dissolve or won't dissolve many compounds water won't dissolve or won't dissolve well. Such as nonpolar and hydrophobic substances.well. Such as nonpolar and hydrophobic substances.

Hydrophilic and Hydrophilic and Hydrophobic SubstancesHydrophobic Substances

• A A hydrophilichydrophilic substance substance– Has an affinity for waterHas an affinity for water– Water “loving”Water “loving”– Dissolves in waterDissolves in water– Example: salt and sugarExample: salt and sugar

• A A hydrophobichydrophobic substancesubstance– Does not have an affinity for waterDoes not have an affinity for water– Water “fearing”Water “fearing”– Does NOT dissolve in waterDoes NOT dissolve in water– Example: OilExample: Oil

REVIEWREVIEW

•Where is the Polar Where is the Polar Covalent Bond in Covalent Bond in water?water?

•What is the What is the difference btw a difference btw a ““POLAR COVALENT POLAR COVALENT BONDBOND” and a ” and a ““NONPOLAR NONPOLAR COVALENT BONDCOVALENT BOND??

Dissociation of water Dissociation of water molecules leads to acidic molecules leads to acidic and basic conditions that and basic conditions that affect living organismsaffect living organisms

• DissociationDissociation = the separation of = the separation of ions when an ionic compound ions when an ionic compound dissolvesdissolves

H2O H+ (hydrogen ion) + OH- (hydroxide

ion) H+ + H2O H3O (hydronium ion)

AcidsAcids

•Number of Number of hydronium ions in hydronium ions in solutions is greater solutions is greater than the than the number of hydroxide ionsnumber of hydroxide ions

•HCl HCl H H++ + Cl + Cl--

BasesBases

•Number of Number of hydroxide ions in hydroxide ions in solution is greater solution is greater than the than the number of hydronium ionsnumber of hydronium ions

•NaOH NaOH Na Na++ + OH + OH--

Acids and BasesAcids and Bases• An An acid acid

– compound that releases/donates a proton (H+) when compound that releases/donates a proton (H+) when dissolved in water dissolved in water

• Increases H+ concentration in solutionIncreases H+ concentration in solution• Ex: HClEx: HCl

• A A basebase– compound that accepts H+ and removes them from a compound that accepts H+ and removes them from a

solutionsolution– Is any substance that reduces the hydrogen ion Is any substance that reduces the hydrogen ion

concentration of a solutionconcentration of a solution• The more basic the solution, the higher the OH- The more basic the solution, the higher the OH-

concentrationconcentration• Ex: NaOHEx: NaOH

• pHpH– Measure of acidity or alkalinity of an aqueous solutionMeasure of acidity or alkalinity of an aqueous solution

pH ScalepH Scale• Measures how acidic or basic a substance Measures how acidic or basic a substance

is:is:– Determined by the concentration of H+ ions Determined by the concentration of H+ ions

within a solution within a solution – Uses a numerical scale of 1 to 14 scaleUses a numerical scale of 1 to 14 scale

• Scale:Scale:– 1 – 7: ACIDIC1 – 7: ACIDIC– 7 – 8: NEUTRAL 7 – 8: NEUTRAL – 8 – 14: BASIC 8 – 14: BASIC

• BuffersBuffers –– resist pH changes resist pH changes– Can accept OR donate H+Can accept OR donate H+– Important in humans…why?Important in humans…why?

• the the lowerlower the pH the stronger the the pH the stronger the acidacid

• the the higherhigher the pH the stronger the the pH the stronger the basebase

• pH pH 7.0 is neutral7.0 is neutral

BuffersBuffers• BuffersBuffers

– substances that minimize substances that minimize changes in [ ] of H+ and OH- changes in [ ] of H+ and OH- ions in a solutionions in a solution

– Buffers keep a neutral pH (pH Buffers keep a neutral pH (pH 7)7)

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

• The pH scale and pH values of The pH scale and pH values of various aqueous solutionsvarious aqueous solutions

Each increase or decrease is

10x

•Acids = low pH #’sAcids = low pH #’s– HIGH [ ] of H+HIGH [ ] of H+

•Bases = High pH #’s Bases = High pH #’s – HIGH [ ] of OH- HIGH [ ] of OH-

Remember….Remember….

•A…..B…. In the alphabet and A…..B…. In the alphabet and 1….141….14

•A= 1A= 1stst letter (H+ has 1 letter) letter (H+ has 1 letter)•B= 2B= 2ndnd letter letter (OH- has 2 letters) (OH- has 2 letters)

Real Life Example….Real Life Example….The Threat of Acid The Threat of Acid

PrecipitationPrecipitation•Acid precipitationAcid precipitation

– Refers to rain, snow, or fog Refers to rain, snow, or fog with a pH lower than pH 5.6with a pH lower than pH 5.6

– Is caused primarily by the Is caused primarily by the mixing of different pollutants mixing of different pollutants with water in the airwith water in the air

• Acid precipitationAcid precipitation– Can damage life in Earth’s Can damage life in Earth’s

ecosystemsecosystems