Water

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.

Cohesion http://www.realeyz.com/photo/macro/photos/leaf_drops.jpg

Adhesion http://www.nano-world.org/frictionmodule/content/0200makroreibung/0600adhesionmodel/bild1.gif

Surface tension - measure of how difficult it is to stretch or break surface of water.

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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 - measure of concentration of OH- and H+ in solution. 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 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

After acid precipitation Before 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.

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