The Extraordinary The Extraordinary Properties of WaterProperties of Water

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The extraordinary properties of The extraordinary properties of WaterWater

A water molecule (HA water molecule (H22O), is made O), is made

up of three atoms: one oxygen up of three atoms: one oxygen (O) and two hydrogen (H).(O) and two hydrogen (H).

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H

HO

The extraordinary properties of The extraordinary properties of WaterWater

The polarity of water is due The polarity of water is due to: to: – Polar covalentPolar covalent bonds bonds– Uneven distribution of Uneven distribution of

the electrons in the the electrons in the molecule:molecule: The The oxygenoxygen (O) end (O) end

carries a slightly carries a slightly negativenegative (-) charge. (-) charge.

and the and the hydrogenhydrogen (H) (H) ends carry a slightly ends carry a slightly positivepositive (+) charge. (+) charge.

+

+

-

The salt is held in solution by being surrounded by the water molecules

Universal SolventUniversal Solvent

Water is called the Water is called the ““universal solventuniversal solvent” ” because more because more substances are substances are known to dissolve in known to dissolve in water than any other water than any other substance.substance.

It is due to waters It is due to waters polarity.polarity.

Nonpolar and PolarNonpolar and Polar

The difference between a The difference between a polarpolar (water) and (water) and nonpolarnonpolar (ethane) molecule is due to the unequal (ethane) molecule is due to the unequal sharing of electrons within the polar molecule. sharing of electrons within the polar molecule.

NonpolarNonpolar molecules have electrons molecules have electrons equally sharedequally shared within their covalent bonds. within their covalent bonds.

Therefore, nonpolar and polar molecules will not Therefore, nonpolar and polar molecules will not mixmix

Oil and WaterOil and Water!!

The extraordinary properties of The extraordinary properties of WaterWater

What are they?What are they?

CohesionCohesion is the property of water that causes it to be attracted to itself.

•Surface tension, a measure of the strength of water’s surface, is the direct result of cohesion.

•The strong film on the surface of water is a result of the attraction between water molecules. This property allows insects to walk on the surface of water. It also allows creation of waves (which permits the diffusion of oxygen into lakes and seas).

Cohesion

Adhesion

•Water is not only attracted to itself, but will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton.

•Water molecules will “tow” each other along when in a thin glass tube. This is called capillary action. This is the same process by which plants and trees remove nutrients from the soil, and paper towels soak up water.

.

Adhesion

Cohesion and Adhesion TogetherCohesion and Adhesion Together

Creates the meniscus in the graduated cylinder

Moves water up a tree

• Because water molecules are so strongly attracted to each other, the temperature of water changes slowly. •The large percentage of water in living things acts like an insulator, keeping the temperature constant.•Causes winds on a local and global scale.

High Specific Heat

http://www.ec.gc.ca/water/index.htm

““Water vapor forms a Water vapor forms a kind of globalkind of global

‘ ‘blanket’ which helps blanket’ which helps to keep the earth to keep the earth warm. Heat radiated warm. Heat radiated from the sun-warmed from the sun-warmed surface surface

of the earth is of the earth is

absorbed and held absorbed and held

by the vapor.”by the vapor.”

High Heat of Vaporization• The heat of vaporization refers to the amount of

energy required to convert 1g of water from a liquid to a gas.

•In order for water to evaporate, hydrogen bonds must be broken. As water evaporates, it removes a lot of heat with it. This allows organisms to cool themselves by evaporation (sweat)

Water is Less Dense as a Solid

•Ice is less dense as a solid than as a liquid and, therefore, floats on water.

•Bodies of water freeze from the top down . The floating ice provides insulation from extremely cold temperatures and allows living things to survive in the cold water under the ice.

http://www.nyu.edu/pages/mathmol/modules/water/info_water.html

Water is Less Dense as a Solid

Water Ice

Importance to BiologyImportance to Biology HomeostasisHomeostasis Constant physiological condition of Constant physiological condition of

cells, organisms, global ecosystemscells, organisms, global ecosystems– a. Makes a good insulatora. Makes a good insulator– b. Allows for separation of areasb. Allows for separation of areas– c. Universal solvent (polarity)c. Universal solvent (polarity)– d. Coolant (sweat)d. Coolant (sweat)– e. Ice protects against temperature e. Ice protects against temperature

extremesextremes– f. Most abundant compound in living f. Most abundant compound in living

things!!things!!

pH: A look at Acids and BasespH: A look at Acids and Bases

An An acidacid is a substance that is a substance that increases the concentration of increases the concentration of hydrogen ions (H+) in water or hydrogen ions (H+) in water or donates a proton.donates a proton.

A A basebase is a substance that is a substance that decreases the concentration of decreases the concentration of hydrogen ions, in other words, hydrogen ions, in other words, increasing the concentration of increasing the concentration of hydroxide ions OH- or accepts hydroxide ions OH- or accepts a proton.a proton.

What is pH?What is pH?

The pH scale ranges from The pH scale ranges from 00 on the on the acidic endacidic end to to 1414 on the on the basic endbasic end, a solution is , a solution is neutralneutral if its pH if its pH is is 77. .

At pH 7, water contains equal concentrations of At pH 7, water contains equal concentrations of H+ and OH- ions.H+ and OH- ions. – Substances with a pH less than 7 are acidic Substances with a pH less than 7 are acidic – Substances with a pH higher than 7 are basicSubstances with a pH higher than 7 are basic– The pH scale is a log scale so a change of one pH unit The pH scale is a log scale so a change of one pH unit

means a 10x change in the concentration of hydrogen means a 10x change in the concentration of hydrogen ions.  ions. 

pH ScalepH Scale

Biological ImportanceBiological Importance

Living thingsLiving things are extremely sensitive to pH are extremely sensitive to pH and function best when solutions are nearly and function best when solutions are nearly neutral (some exceptions). Most living neutral (some exceptions). Most living matter has a matter has a pH of about 7.2. pH of about 7.2. 

Water's ability to Water's ability to accept, carry and release accept, carry and release protonsprotons in acid-base reactions is another of in acid-base reactions is another of its chemical properties that makes it very its chemical properties that makes it very suitable as a suitable as a biological mediumbiological medium. .