•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

http://chem.lapeer.org/Chem1Docs/MolQuiz.html

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

H2O ----> H+ + OH-

– due to hydrogen bonding hydrogen atoms actually shift from one water molecule to another

H2O + H2O ---> H3O+ + 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 4H+ > OH- decreases pHH+ < OH- increases pHH+ = 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 7.38-7.42) therefore your body will decrease respiration to maintain homeostasis