Water and the Fitness of the Environment Chapter 3

I. Water Molecule What is a polar molecule? How does the polarity of water effect this molecule?

II. Properties of Water What are the four characteristics of water that emerge due to this hydrogen bonding? Water is cohesive Moderation of temperature Water expands when it freezes Water is a versatile solvent

A. Water is Cohesive Cohesion Adhesion due to hydrogen bonding water molecules are attracted to other water molecules Surface tension Adhesion Attraction of water molecules to a surface

B. Moderation of Temperature Water has a high specific heat. What is specific heat? Why is it high for water? Where do we see this characteristic in our lives? Lake Michigan Boiling water

B. Moderation of Temperature Evaporative Cooling - molecules with the greatest kinetic energy are the most likely to leave as a gas Ex: evaporation of sweat from human skin Heat of vaporization - quantity of heat a liquid must absorb to be converted to a gas Helps to moderate Earth’s climate Accounts for the severity of steam burns of the skin

C. Water Expands When It Freezes Why is water less dense as a solid than as a liquid?

Important factors that result from water’s expansion as it freezes: Prevents deep bodies of water from freezing from the bottom up As water freezes it releases heat to water below and insulates it As water freezes H bonds form releasing heat. As ice melts H bonds break absorbing heat. Both of these factors make seasonal transitions less abrupt

D. Water is a Versatile Solvent Polar compounds dissolve in water. Nonpolar compounds do not dissolve in water.

III. Acids Bases and pH Water molecules dissociate into H+ and OH- At equilibrium the [H+ ] = [OH-] The molar concentrations of these ions = 10-7, which represents a neutral solution pH of a solution = -log [H+ ] Therefore what is the pH of a neutral solution? 7

Acids Bases Increase the relative [H+ ] of a solution [H+ ] > [OH-] in an acidic solution Remove [OH-] from a solution which increases the relative [H+ ] For example the acid HCl in a solution converts to [H+ ] + Cl- pH of acidic solution<7 Bases Reduce the relative [H+ ] of a solution [H+ ] < [OH-] in a basic solution Bases either reduce [H+ ] directly…….. NH3 + H+ --> NH4 or indirectly ……... NaOH --> Na+ + OH- pH of basic solution > 7

How much greater is the [H+ ] in a solution with a pH of 2 than a solution with a pH of 6? 10,000

Water Transport in Plants