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Chemistry of Water

Chapter 3: Water and the Fitness of the Environment

By Group 3: Sarah Rios, David Jung, and Steven Lee


Concept 3.1: The Polarity of Water molecules Results in Hydrogen Bonding (pg 47-48)

Water has 2 hydrogen atoms joined to an oxygen atom by a covalent bond. It is a polar molecule, which means the two opposite ends of the molecule have an opposite charge. The 

oxygen region has a partial negative charge  (δ− ) and hydrogen has a partial positive (δ+).

Concept 3.2: Four Emergent Properties of Water Contribute to Earth’s Fitness for Life

-Cohesion (pg 48-49)

Cohesion is the property that holds the molecule together using very weak hydrogen bonds. The bonds continuously break and reform in a few trillionths of a second, making water more structured than other liquids. Adhesion –the clinging of one substance to another- helps counter the pull of gravity. Surface Tension is the elastic tendency of liquids which makes them acquire the least surface area possible.

-Moderation of Temperature (pg 49-50)

Water moderates air temperature by absorbing warmer air and releasing stored heat. Kinetic energy is the energy of motion, and the faster a molecule moves the greater it’s kinetic energy. Heat is the measure of total kinetic energy, and temperature measures the intensity of heat due to average kinetic energy. Water has a high specific heat, which is the amount of heat that must be absorbed or lost for the temperature of a substance to change by 1 degree Celsius. Heat of vaporization is the quantity of heat a liquid must absorb to converted to gas. Evaporative Cooling is the reduction in temperature resulting from evaporation of liquid.


Insulation of Bodies of Water by Floating Ice (pg 50-51)

Ice is less dense than liquid water, which is uncommon for most liquids, this is because hydrogen bonds expand into crystal formations at low temperatures. This causes ice to float, and life can exist underneath frozen surfaces of lakes and oceans.

-The Solvent of Life (pg51-53)

Water is a versatile solvent, which means it is a useful dissolving agent for many solutions and solutes. A solution is a mixture of two or more solutions, a solute is the substance dissolved by the solvent. This is because of the polarity of the molecules. When ions are dissolved, a sphere of water molecules form around it called a hydration shell. Substances with an affinity for water are hydrophilic and substances that avoid water are hydrophobic. Sometimes molecules in cells are so large that they do not dissolve, and instead remain suspended in the solution, called a colloid.

A mole represents an exact number of objects, and is used to measure the amount of a substance. Molarity is the number of moles per solute liter. Molecular mass is calculated by the sum of all atoms in a molecule

Concept 3.3: Dissociation of Water Molecules Leads to Acidic Molecules Leads to Acidic and Basic Conditions That Affect Living Organisms

-Effects of Change in pH (pg 53-55)

Water can dissociate into H+ and OH-. Concentration of hydrogen is expressed as pH and is measured on a scale of 0- 14 where pH= -log[H+].  7= neutral pH, less than 7= acidic and more than 7 is a base. Buffers are substances that minimize changes in concentration of H+ and OH- in a solution. Buffers work by accepting hydrogen ions from the solution or donating them to it as needed.

-The Threat of Acid Precipitation (pg 55-56)  

Acid Precipitation refers to rain, fog, or snow that has a pH lower than 5.6. Acid precipitation is caused by presence of sulfur oxide and nitrogen oxide that react with water to form strong acids. Precipitation with a low pH can damage life in lakes and streams and wash away calcium and magnesium ions that normally act as buffers in the soil and are essential for plant growth.