50-95% of any functioning living system. 98% of water on earth is in liquid form.

Characteristics Polar covalent molecule Hydrogen end: partial+ charge Oxygen end: partial - charge

Forms numerous hydrogen bonds

Special Properties Cohesion –Hydrogen bonding causes water molecules to “stick” to other water molecules. –Causes surface tension. Adhesion –Water molecules “stick” to other atoms. –Causes capillary action.

Surface Tension –A measure of how difficult it is to stretch or break the surface of a liquid.

Moderation of Temperature Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler. –Molecules in cooler air speed up at the expense of the kinetic energy of the warmer air and vice versa –Ice cubes cool drinks by absorbing energy from the drink. Remember a kilocalorie is the quantity of heat required to raise the temperature of 1 kilogram of water by 1 degree Celsius.

High Specific Heat –Hydrogen bonding restricts movement, therefore it resists rapid change –High thermal conductivity –Good for organisms because it is easier to maintain body temperature Specific Heat of a substance is the amount of heat that must be absorbed or lost for 1gram of that substance to change its temperature by 1 degree Celsius

Evaporative Cooling Molecules moving fast enough to overcome the attraction to stay close together can depart the liquid and enter the air as gas –Heat of Evaporation is the quantity of heat a liquid must absorb for 1 gram of it to be converted from the liquid to the gaseous state. Due to hydrogen bonds, water has a high heat of vaporization and helps moderate Earth’s climate As a liquid evaporates, the surface of the liquid that remains behind cools down –Helps regulate body temperature –Contributes to the stability of lake and pond temperatures

The ability of ice to float because of the expansion of water as it solidifies is important to the environment and life as we know it. Water is 10% less dense as a solid than a liquid!

The Solvent of Life Polar compounds are dissolved by the water in biological fluids such as blood, the sap of plants, and the liquid within all cells. In an Aqueous Solution water is the Solvent The sphere of water molecules around each ion is called a hydration shell.

Solute Concentration in Aqueous Solutions Molarity is the number of moles of solute per liter of solution. Interactive mole practice

Hydrophilic and Hydrophobic Substances Hydrophobic –Water fearing –Nonionic and nonpolar substance repel water –Hydrophobic molecules of the cell membranes keep the cell membrane intact. Hydrophilic –Water loving –Any substance that has an affinity for water –Colloids, a mixture of a stable suspension of fine particles in a liquid, do not dissolve in water thus allowing large molecules of cells to remain suspended within the cell

Dissociation Dissociation of water into a hydrogen ion and a hydroxide ion H 2 O ---->H + + OH - –due to hydrogen bonding hydrogen atoms actually shift from one water molecule to another H 2 O + H 2 O ---> H 3 O + + OH - Leads to acidic and basic conditions that affect living organisms. –Acids increase the hydrogen ion concentration of a solution. –Bases increase the hydroxide ion concentration of a solution.

pH Scale pH: “power of hydrogen” If H concentration Is 4, than pH is 4 H + > OH - decreases pH H + < OH - increases pH H + = OH - pH remains the same Buffers: substances that minimize H+ and OH- concentrations –Controls chemical reactions –Maintains homeostasis

Biological Application Acid Rain –Precipitation with a pH less than 5.6 –Can reduce biodiversity of life in lakes and streams. –Acid precipitation falling on land washes away calcium and magnesium ions that help buffer the soil and are essential nutrients for plant growth.

Biological Application Bicarbonate Buffering system in blood Increase of H + such as in fat metabolism causes equilibrium shift to the left and an increase of carbon dioxide therefore your body will increase respiration to maintain homeostasis. Hyperventilation or an increase in respiration decreases carbon dioxide causing an equilibrium shift to the left therefore blood pH increases (normal ) therefore your body will decrease respiration to maintain homeostasis