Properties of Water

VCE Biology

Britt Gow, 2014

Water - A unique compound

• Most abundant compound in our bodies

• Main solvent for many organic molecules

• Ideal medium for chemical reactions (metabolism)

• Each hydrogen atom is linked by strong covalent bonds

• A ‘polar’ molecule (O2 is slightly negative and H is slightly positive)

Water covers 70% of the earth’s surface

Human Body is 55 to 78% water

Water = H20 = 2 hydrogen atoms and 1

oxygen atom in each molecule

2 Hydrogen and 1 Oxygen atoms

Universal Solvent

High Heat capacity

Most dense at 4 degrees Celsius

Surface tension

Cohesive

• Water molecules are attracted to each other by hydrogen bonds, which are continually breaking and reforming.

• At 4 degrees C the molecules no longer form hydrogen bonds and they form a lattice.

• At 100 degrees C, hydrogen bonds no longer form and water is converted to a gaseous state (steam).

Cohesion and adhesion

Capillary Action

Water Cycle

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Watercycle.shtml

On average, water spends 9 days in the atmosphere.

About 1.7% of all the earth’s water is groundwater and can be stored for many

thousands of years.

Key Ideas

• A synchrotron is a ‘super microscope’ used to examine molecules in fine detail.

• All metabolic reactions occur in watery solutions.

• Water can occur in three different states under natural conditions.

• The pH scale is a measure of hydrogen ions in solution (can extend below 1 and above 14)

• pH = 1 (acid) neutral = 7 pH = 14 (alkaline)

copyright cmassengale 17

Questions• What are the special characteristics of light

produced by a synchrotron?

• Explain why ice is less dense than water.

• Explain how this difference in density is of vital importance to organisms that live in water.

• What name is given to a solution that has equal numbers of hydrogen (H+) and hydroxide ions (OH-)?

• What general name is given to solutions that have many more hydrogen ions that hydroxide ions?