The Properties of WaterThe Properties of Water

•A water molecule (H2O), is made up of 33 atoms --- one oxygen and two hydrogen.

H

HO

1. Water is Polar1. Water is Polar

• In each water molecule, the oxygen oxygen atom attracts moreatom attracts more than its "fair share" of electronselectrons

• The oxygenoxygen end “acts” negativenegative• The hydrogenhydrogen end “acts” positivepositive• Causes the water molecule to be

POLARPOLAR• However, Water is neutralneutral (equal

number of e- and p+) --- Zero Net Zero Net ChargeCharge

2. Hydrogen Bonds 2. Hydrogen Bonds attract other Water attract other Water

MoleculesMolecules• Formed between a Formed between a

highly highly Electronegative atom Electronegative atom of a polar molecule of a polar molecule and a Hydrogen and a Hydrogen

• One hydrogen bond One hydrogen bond is weak , but many is weak , but many hydrogen bonds are hydrogen bonds are strongstrong

3. Interaction Between 3. Interaction Between Water MoleculesWater Molecules

Negative Oxygen end of one water molecule is Negative Oxygen end of one water molecule is attracted to the Positive Hydrogen end of attracted to the Positive Hydrogen end of

another water molecule to form a HYDROGEN another water molecule to form a HYDROGEN BONDBOND

4. At sea level, pure water boils 4. At sea level, pure water boils at 100 °C and freezes at 0 °C. at 100 °C and freezes at 0 °C.

• It takes a longer time for water It takes a longer time for water to boil at higher elevations to boil at higher elevations (lower atmospheric pressure). (lower atmospheric pressure).

• For this reason, an egg will For this reason, an egg will take longer to boil at higher take longer to boil at higher altitudesaltitudes

5. Cohesion5. Cohesion• Attraction between particles of Attraction between particles of

the same substance (the same substance ( why water why water is attracted to itself)is attracted to itself)

• Results in Surface tension (a Results in Surface tension (a measure of the strength of measure of the strength of water’s surface)water’s surface)

• Produces a surface film on water Produces a surface film on water that allows insects to walk on that allows insects to walk on the surface of water the surface of water

Cohesion cont…Cohesion cont…

Helps insects walk across water

6. Adhesion6. Adhesion• Attraction between two different Attraction between two different

substances.substances.• Water will make hydrogen bonds with other Water will make hydrogen bonds with other

surfaces such as glass, soil, plant tissues, surfaces such as glass, soil, plant tissues, and cotton. and cotton.

• Capillary action occurs when water Capillary action occurs when water molecules will “tow” each other along when molecules will “tow” each other along when in a thin glass tube.in a thin glass tube.

• Example: transpiration is the process which Example: transpiration is the process which plants and trees use to remove water. As plants and trees use to remove water. As water evaporates form the leaves then more water evaporates form the leaves then more water is pulled in from the roots.water is pulled in from the roots.

Adhesion Also Causes Adhesion Also Causes Water to …Water to …

Form spheres & hold onto plant leaves

Attach to a silken spider

web

7. High Specific Heat7. High Specific Heat• This is the mount of heat needed This is the mount of heat needed

to raise or lower 1g of a to raise or lower 1g of a substance 1° C.substance 1° C.

• Water resists temperature Water resists temperature change very well, both for change very well, both for heating and cooling.heating and cooling.

• Water can also absorb or release Water can also absorb or release large amounts of heat energy large amounts of heat energy with little change in actual with little change in actual temperature.temperature.

7. High Heat of 7. High Heat of VaporizationVaporization

• Vaporization is the amount of Vaporization is the amount of energy needed to convert 1g or a energy needed to convert 1g or a substance from a liquid to a gassubstance from a liquid to a gas

• In order for water to evaporate, In order for water to evaporate, hydrogen bonds must be broken hydrogen bonds must be broken and this takes a lot of heat energy.and this takes a lot of heat energy.

• As water evaporates, it removes a As water evaporates, it removes a lot of heat with it, used in lot of heat with it, used in sweating to cool you bodysweating to cool you body

High Heat of Vaporization High Heat of Vaporization cont…cont…

• Water's heat of vaporization is 540 cal/g.540 cal/g.

• In order for water to evaporate, In order for water to evaporate, each gram of the water must each gram of the water must GAIN 540 calories (temperature GAIN 540 calories (temperature doesn’t change --- 100doesn’t change --- 100ooC).C).

• As water evaporates, it removes As water evaporates, it removes a lot of heat with it (cooling a lot of heat with it (cooling effect).effect).

•Water vapor Water vapor forms a kind of global ‘‘blanket” which helps to keep the Earth warm.

•Heat radiated from the sun Heat radiated from the sun warmed surface of the earth is

absorbed and held absorbed and held

by the vaporby the vapor.

8. Water is Less Dense as a 8. Water is Less Dense as a SolidSolid

• Ice is less dense Ice is less dense as a solid than as a liquid (ice floats)

• Liquid water has hydrogen bonds hydrogen bonds that are constantly being broken constantly being broken

and reformed.and reformed.

• Frozen water Frozen water forms a crystal-like crystal-like

latticelattice whereby molecules are set at fixed distances.

HomeostasisHomeostasis

• Water is important in maintaining Water is important in maintaining homeostasis in organisms because it:homeostasis in organisms because it:a. Makes a good insulatora. Makes a good insulatorb. Resists temperature changeb. Resists temperature changec. Is the Universal solventc. Is the Universal solventd. Is used as a Coolantd. Is used as a Coolante. Is used when an Ice to protect e. Is used when an Ice to protect

against temperature against temperature extremes (insulates frozen lakes)extremes (insulates frozen lakes)

Acids, Bases and pHAcids, Bases and pHOne water molecule in 550 million One water molecule in 550 million

naturally dissociates into a naturally dissociates into a Hydrogen Ion (H+) and a Hydrogen Ion (H+) and a Hydroxide Ion (OH-) causing acids Hydroxide Ion (OH-) causing acids and bases.and bases.

Hydrogen Ion Hydroxide IonHydrogen Ion Hydroxide Ion Acid BaseAcid Base

H2O H+ + OH-

1. The pH Scale1. The pH Scale• Indicates the concentration of Hconcentration of H++ ions ions

in a solutionin a solution• It ranges from 0 – 140 – 14• pH of 7 is neutral (pure water)7 is neutral (pure water)• pH 0 up to 7 is an acid 0 up to 7 is an acid … hi in H+ ions

• pH above 7 – 14 is babove 7 – 14 is basic…hi in OH- ions

• Each pH unit represents a factor of 10X 10X change in concentration

• Ex. pH 5 is stronger than a pH of 6, 4 Ex. pH 5 is stronger than a pH of 6, 4 is 100x stronger than 6is 100x stronger than 6

2. Acids2. Acids

•Acids Acids produce produce lots of lots of H H+ + ions ions in solutionin solution

3. Bases3. Bases

• Bases Bases have a pH of 8 to 14 8 to 14 and and Contain lots of OHlots of OH--

ions ions and fewer H+ ions in solution.

4. Buffers4. Buffers• Weak acids or bases that react with Weak acids or bases that react with

strong acids or bases to prevent strong acids or bases to prevent sharp, sudden changes in pH is sharp, sudden changes in pH is called neutralization= H ions + OH called neutralization= H ions + OH ions=water, ex. Antacids.ions=water, ex. Antacids.

• Buffers are also Produced naturally Buffers are also Produced naturally by the body to maintain by the body to maintain homeostasis.homeostasis.