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