Water and the Fitness of the Environment

Polarity of Water Water is a polar molecule Water is a polar molecule Hydrogen of one H 2 O is attracted to the Oxygen of another H 2 O Hydrogen of one H 2 O is attracted to the Oxygen of another H 2 O Therefore, hydrogen bonding occurs Therefore, hydrogen bonding occurs

Properties of Water Water has 4 properties that make Earth a fitting environment for life: Water has 4 properties that make Earth a fitting environment for life: –High surface tension/Cohesive behavior –Ability to stabilize temperature –Expansion upon freezing –Versatility as a solvent for life

1. Cohesion Cohesion: Cohesion: –Hydrogen bonds hold water together in liquid form –Responsible for transport of water against gravity in plants

Cohesion Adhesion = clinging of one substance to another Adhesion = clinging of one substance to another –Cohesion = adhesion of water to itself Surface Tension = how hard it is to stretch or break the surface of a liquid Surface Tension = how hard it is to stretch or break the surface of a liquid

2. Ability to Stabilize Temperatures Water… Water… –Absorbs heat from air that is warmer than itself –Releases stored heat to air that is cooler than itself

Ability to Stabilize Temperatures Water’s high specific heat Water’s high specific heat –Specific heat amount of heat that must be absorbed or lost for 1g of that substance to raise its temperature by 1C amount of heat that must be absorbed or lost for 1g of that substance to raise its temperature by 1C – Because of its high specific heat (due to hydrogen bonding) water resists temperature change LOTS of hydrogen bonds have to be broken before water molecules can start moving faster LOTS of hydrogen bonds have to be broken before water molecules can start moving faster

Ability to Stabilize Temperatures Application: Application: –Large body of water can absorb LOTS of heat from the sun –Then, the gradually cooling water warms the air at night and in the winter Mild climate of coastal areas Mild climate of coastal areas –Ocean, lake, pond temperatures remain stable – IMPORTANT!

3. Expansion Upon Freezing Water is less dense as a solid than as a liquid: Water is less dense as a solid than as a liquid: –Because of hydrogen bonding! –Because of hydrogen bonding! Therefore, ice floats Therefore, ice floats Ice: Ice: –Each water molecule bonded to max of 4 “partners” Water: Water: –Bonds are constantly breaking and reforming

Expansion Upon Freezing Application and Importance: Application and Importance: –Allows marine life to continue to live even when the top layer of water is frozen –Ice acts as an insulator

4. Solvent of Life Solution: Solution: –A liquid that is a homogeneous mixture of 2 or more substances Solvent: Solvent: –The dissolving agent –Ie. water Solute: Solute: –Substance that is dissolved –Ie. Kool-aid powder

Solvent of Life Aqueous Solution: Aqueous Solution: –A solution in which water is the solvent Water is NOT a universal solvent Water is NOT a universal solvent –Why not?

Solvent of Life Hydrophilic: Hydrophilic: –“water-loving” –Polar and ionic compounds Hydrophobic: Hydrophobic: –“water-fearing” –Nonpolar compounds

The pH Scale The dissociation of water The dissociation of water H 2 O  H + + OH - In water: In water: [H + ] = [OH - ]

The pH Scale Acid: Acid: –A substance that increases the H+ concentration of a solution [H + ] > [OH - ] Base: Base: –A substance that decreases the H+ concentration of a solution [H + ] < [OH - ]

The pH Scale Logarithmic scale of 0 – 14 Logarithmic scale of 0 – 14 Neutral pH = 7 Neutral pH = 7 Acidic pH = <7 Acidic pH = <7 –More H + ions Basic pH = > 7 Basic pH = > 7 –Fewer H + ions pH declines as H + concentration increases pH declines as H + concentration increases

Acid Precipitation pH of normal rain = 5.6 pH of normal rain = 5.6 pH of acid rain = as low as 1.5 pH of acid rain = as low as 1.5 (Sulfur oxides or nitrogen oxides) + water  acids Human blood pH = 7.4 Human blood pH = 7.4 –7.0 or 7.8 = death! Importance: Importance: –Aquatic animals, plants, etc…