Properties
• Water - polar molecule - opposite ends have opposing charges.
• One end - slightly positive; other - slightly negative.
• Ends attracted to one another and held together by a hydrogen bond.
Slightly negative
Slightly positive
• Water molecules stick because of hydrogen bonding (cohesion)
• Water molecules stick to other substances (adhesion)
• Both responsible for the water’s ability to travel up plants.
http://www.realeyz.com/photo/macro/photos/leaf_drops.jpg
Cohesion
http://www.nano-world.org/frictionmodule/content/0200makroreibung/0600adhesionmodel/bild1.gif
Adhesion
•Surface tension - measure of how difficult it is to stretch or break surface of water.
http://gallery.hd.org/_exhibits/natural-science/_more2006/_more01/meniscus-on-water-surface-tension-supporting-steel-paperclip-in-drinking-glass-tumbler-beaker-6-AJHD.jpg
Heat•Heat - total quantity of kinetic
energy due to motion in matter.
•Temperature - intensity of heat due to average kinetic energy of molecules (measured in Celsius)
•Specific heat - amount of heat absorbed or lost for 1 g of substance to change temperature 1o C.
http://www.jlcomicart.de/images/HeatWave1.jpg
• Water - high specific heat.
• High heat of vaporization (amount of heat liquid must absorb for 1 g to be converted to gas)
• Water has high heat of vaporization because weak hydrogen bonds must break to go from liquid to gas.
http://www.geo.arizona.edu/xtal/nats101/9_7.jpg
• Water keep Earth’s climate stable due to evaporative cooling.
• When liquid evaporates, surface of liquid left behind cools.
• Example - sweating causes body to cool down; as sweat evaporates, surface of skin is cooled off.
• “Evaporation causes cooling”
http://www.brassmonkeycooling.co.uk/images/sweating.gif
pH
• Hydrogen breaks into hydroxide ions (OH-) and hydronium ions (H3O+)
•pH - measure of concentration of OH- and H+ in solution.
• Increased H+ - more acidic; increased OH- - more basic.
Acidic Basic
• pH scale - 0 (most acidic) to 14 (most basic).
• Stomach acid - pH of 2 (same as lemon juice); oven cleaner - pH around 13.
• As concentration of H+ increases, pH decreases.
• Neutral pH - 7 (pure water)
Buffers
•Buffers resist changes in concentrations of (OH-) and H+
• Buffers in blood help keep pH of blood close to 7.4.
• If pH rises above 7.7 or below 7, person will not survive.
• Buffers prevent this.
http://www.lightandgrow.com/images/ph%20buffers.jpg
Importance of pH
• Rain not contaminated has pH around 5.6.
• Because of wastes in atmosphere (from burning fossil fuels and pollution), acid precipitation can result (pH less than 5.6)
• Acid precipitation can damage aquatic life and change soil chemistry.
Burning of fossil fuels by factories
Trees damaged by acid precipitation
Before acid precipitation
After acid precipitation
pH in Biology
• Body needs to maintain specific pH in order to function.
• Acidosis – acidic pH – too low can cause death.
• Respiratory acidosis – too much carbon dioxide builds up in the body; body becomes acidic.
• Lactic acidosis – build-up of lactic acid; body will start to breathe deeper to get rid of excess.
• Lactic acid causes muscle cramps.
http://www.toyomavello.com.sg/Diseases.jpg