The Chemistry of Life Properties of Water

The Water Molecule Neutral Charge –All Molecules Are Neutral

The Water Molecule PolarityPolarity –A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. –The bonds between O and H are polar covalent. Oxygen has a stronger pull on electrons than Hydrogen. (-) (+)

Hydrogen Bonds Polar water molecules act like magnets and attract each otherPolar water molecules act like magnets and attract each other Hydrogen BondsHydrogen Bonds –The attraction of the Hydrogen end (+) of one molecule for the Oxygen end (-) of another water molecule. –They are the strongest bonds that can form between molecules

Hydrogen Bonds

Cohesion The attraction between molecules of the same substance (e.g. water). Allows some insects and spiders to walk on water.

Adhesion Attraction between molecules of different substancesAttraction between molecules of different substances Responsible for Capillary forces in plantsResponsible for Capillary forces in plants

High Specific Heat Amount of heat needed to raise or lower 1g of a substance 1° C. Water resists temperature change, both for heating and cooling.Water resists temperature change, both for heating and cooling. Water can absorb or release large amounts of heat energy with little change in actual temperature.Water can absorb or release large amounts of heat energy with little change in actual temperature.

High Heat of Vaporization Amount of energy to convert 1g or a substance from a liquid to a gas In order for water to evaporate, hydrogen bonds must be broken. As water evaporates, it removes a lot of heat with it. In order for water to evaporate, hydrogen bonds must be broken. As water evaporates, it removes a lot of heat with it. Causes Evaporative CoolingCauses Evaporative Cooling

“ Water vapor forms a kind of global ‘blanket’ which helps to keep the earth warm. Heat radiated from the sun- warmed surface of the earth is absorbed and held by the vapor.”

Water is Less Dense as a Solid Ice is less dense as a solid than as a liquid (ice floats) Liquid water has hydrogen bonds that are constantly being broken and reformed. Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances.

Solutions & Suspensions Water is usually part of a mixture.Water is usually part of a mixture. There are two types of mixtures:There are two types of mixtures: –Solutions –Suspensions

Solution Ionic compounds disperse as ions in waterIonic compounds disperse as ions in water Evenly distributedEvenly distributed SOLUTESOLUTE –Substance that is being dissolved SOLVENTSOLVENT –Substance into which the solute dissolves

Solution

Suspensions Substances that don’t dissolve but separate into tiny pieces.Substances that don’t dissolve but separate into tiny pieces. Water keeps the pieces suspended so they don’t settle out.Water keeps the pieces suspended so they don’t settle out.

Acids, Bases & pH 1 water molecule in 550 million naturally dissociates into a Hydrogen Ion and a Hydroxide Ion1 water molecule in 550 million naturally dissociates into a Hydrogen Ion and a Hydroxide Ion Hydrogen Ion Hydroxide Ion Acid Base Acid Base H 2 O  H + + OH -

The pH Scale Indicates the concentration of H + ions Ranges from 0 – 14 pH of 7 is neutral pH 0 – 6.99 is acid … H + pH 7.01 – 14 is basic… OH - Each pH unit represents a factor of 10 change in concentration

Acids Strong Acid = pH 1-3 H + ions

Bases Strong Base = pH 11 – 14 OH - ions

Buffers Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH.Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH. Weak Acid Weak Base

Buffers are Important to Biological Systems Cells can only function in a specific pH Range Slight changes in pH can be harmful to cells and organisms Human Blood has its own buffer system, pH can not exceed 7.8 or drop below 7.0