Notes: Water Chemistry

Water Water is the most important COMPOUND in living organisms! –Most organisms are made up of 70-95% of water Water serves as a form of TRANSPORTATION –Helps move nutrients and other substances in and out of cells Water is a POLAR molecule

What is a Polar Molecule? POLAR: A molecule with a POSITIVE end and a NEGATIVE end Water molecules are attracted to each other by hydrogen bonds –Remember: van der Waals forces

Water Structure Notice that opposite charges attract!

Polar Nature of Water

Water Bonding COHESION – an attraction between the SAME kind of substances –In water: a result of hydrogen bonds –Attraction between water molecules causes SURFACE TENSION

Water Bonding ADHESION – an attraction between DIFFERENT substances Water & Glass Capillary tubes

Properties of Water 1.High surface TENSION 2.Creeps up in thin tubes - CAPILLARY action 3.High heat of VAPORIZATION 4.Resists TEMPERATURE change 5.Water EXPANDS when it freezes 6.Universal SOLVENT

1. High Surface Tension Water is STICKY –Due to cohesion— sticks to itself When hydrogen bonds are broken they quickly reform Water striders using water surface tension when mating.

Surface Tension Causes the drop into a sphere

2. Capillary Action MOVEMENT of water within the spaces of a porous material due to adhesion Occurs because water is “STICKY” to another substance Limited by gravity and the diameter of the capillary (tube) –Smaller the diameter, the greater the effect

Capillary Action Capillary action causes the water to "climb" up this paper towel.

Water Movement in Plants Water moves upward through a plant from roots to leave through a COMBINATION of: –Cohesion –Capillary Action (adhesion)

3. High Heat of Vaporization Water needs a LOT of heat to make liquid water change to a gas state (540 calories)

4. Resists Temperature Change Water can ABSORB a tremendous amount of heat –Moderates our climate –It also takes a long time to cool down In organisms, the ability to control temperature enables cells to maintain a constant internal temperature--Homeostatsis

Water Stores Heat Water heats more slowly and RETAINS heat LONGER than many substances Many organisms release excess heat through evaporation –Sweating carries heat away from the body (HOMEOSTASIS)

5. Water Expands when it Freezes Water EXPANDS when it freezes Ice is LESS dense than liquid water Ice FLOATS in liquid water

6. Universal Solvent Many substances DISSOLVE in water –C–Commonly called the universal solvent. Why?....remember POLARITY of water –B–Because of this, water in nature and in use is rarely pure Many substances are INSOLUBLE in water. Why? They are NOT POLAR and not attracted to water