WATER AND THE FITNESS

OF THE ENVIRONMENT

YOU MUST KNOW…

• THE IMPORTANCE OF HYDROGEN BONDING TO THE PROPERTIES OF WATER

• FOUR UNIQUE PROPERTIES OF WATER, AND HOW EACH CONTRIBUTES TO LIFE ON EARTH

• HOW TO INTERPRET THE pH SCALE

• THE IMPORTANCE OF BUFFERS IN BIOLOGICAL SYSTEMS

CONCEPT 3.1

• THE POLARITY OF WATER MOLECULES RESULTS IN HYDROGEN BONDING

Water H2O• As we know - water

is polar • The end bearing the

oxygen atom has a slightly negative charge while the hydrogen atoms have a slightly positive charge

• Since oxygen is larger, it gives water a slight overall charge called polarity

POLAR BONDING

• Polarity really does allow bonding

• They are hydrogen bonds and they are very weak

• They last for fractions of a second

• Continuously break and reform

• Water has an uneven distribution of electrons between hydrogen and oxygen atoms creating polarity

• Polarity allows bonding• The bonds are very weak

hydrogen bonds • They last for fractions of a

second and continuously break and reform

+

+ -

CONCEPT 3.2

• FOUR EMERGENT PROPERTIES OF WATER CONTRIBUTE TO EARTH’S FITNESS FOR LIFE

EMERGENT PROPERTIES• COHESION ( WORKS WITH

ADHESION AND TRANSPIRATION)• SPECIFIC HEAT• INSULATION OF BODIES OF

WATER BY FLOATING ICE• ACTS AS A SOLVENT -HYDROPHILIC - WATER SOLUBLE

AND INCLUDE IONIC COMPOUNDS AND POLAR MOLECULES

-HYDROPHOBIC – DON’T DISSOLVE IN WATER AND ARE NONPOLAR SUCH AS OILS

COHESION• The natural attraction of a water

molecule to other water molecules is called cohesion

COHESION• Cohesion: attraction between

same molecules, causes molecules to draw inward at surface

• creates surface tension• Can be seen as water droplets

form

ADHESION

• The attraction of a water molecule to another polar molecule is adhesion

• Molecules such as soil and clay (dust)

• Surfaces like glass or paper straws • Certain clothing fibers and … animal

hair

ADHESION

• Adhesion: attraction between different molecules, causes water to bend at the surface and clinging of one substance

to another

ADHESION• Can be seen as water droplets

form on the spider web (another polar surface)

TRANSPIRATION1. We know that gravity is

ALWAYS pulling on objects with mass

2. Yet water can move up a plant with relative ease - How can this happen?

3. The water molecules cling to each other by cohesion and water and minerals cling to the walls of the xylem tubes by adhesion

4. This property of adhesion is called capillary action

Review of Polarity

Polarity hydrogen bonding

cohesion adhesion

surface tension capillary action

Forces

Properties

Forces

SPECIFIC HEAT

• The amount of heat required to raise or lower the temperature of a substance by 1 degree Celsius

• Water exhibits evaporative cooling: removes heat when it evaporates from a surface

• Ex: sweating cools skin

INSULATION

• Water expands during freezing: expands into crystal formation releasing heat

• Ex: rocks broken up by ice creating soil; ice layer protects

fruit from freezing

SOLVENT

• Dissolves many other substances due to polarity

• Differences in charges pulls/pushes substances apart

• HYDROPHILIC SUBSTANCES – are water-soluble and may be polar

• HYDROPHOBIC SUBSTANCES – are nonpolar and do not dissolve in water EX. oils

CONCEPT 3.3

• ACIDIC AND BASIC CONDITIONS AFFECT LIVING ORGANISMS

Acids, Bases and the pH scale

The pH scale measures the concentration of H+ ions (how acidic something is)Ranges from 0-14At 7: H+ ions and OH- ions are equal so it is neutral 0-7: acidic, has more H+ ions 7-14: basic, has more OH- ions

• ACIDS: release H+ when mixed with water

• Sour, corrosive• Ex: HCl, H2SO4

• Always have H at front of formula

• BASES: release OH- when mixed with water

• Bitter, slippery, usually in cleaners

• NaOH, CaOH• Always have OH at end

of formula

What is a buffer?• Buffers are weak acids or bases that

react with strong acids and bases to prevent sharp changes in pH

• Helps to neutralize• Help to control pH in blood, digestive

tract, etc. to maintain homeostasis