The Chemistry of Life Properties of Water

Water A water molecule (H 2 O), is made up of three atoms: one oxygen and two hydrogen. H H O

Properties of Water What are they?What are they?

Properties of Water Polar MoleculePolar Molecule CohesionCohesion AdhesionAdhesion High Specific HeatHigh Specific Heat High Heat of VaporizationHigh Heat of Vaporization Less Dense as a SolidLess Dense as a Solid

The Water Molecule PolarityPolarity –A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. (-) (+)

Hydrogen Bonds Weak attraction between hydrogen (with a positive charge) and something else (negative charge) Holds water molecules to each other. Animation bonds are break and reformhydrogen bonds are break and reform

Hydrogen Bonds

Cohesion The attraction between molecules of the same substance (e.g. water). Allows some insects and spiders to walk on water. Results in:Results in: Surface tension : a measure of the strength of water’s surfaceSurface tension : a measure of the strength of water’s surface

Adhesion Attraction between molecules of different substances (makes water stick to other substances)Attraction between molecules of different substances (makes water stick to other substances) Responsible for Capillary forces in plantsResponsible for Capillary forces in plants Capillary action-water molecules will “tow” each other alongCapillary action-water molecules will “tow” each other along –Ex. In plant stems, meniscus in graduated cylinder, paper towel

High Specific Heat Amount of heat needed to raise or lower 1g of a substance 1° C. Resists temperature changeResists temperature change Can absorb or release large amounts of heat energy with little change in actual temperature.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.

“ 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.

Homeostasis Ability to maintain a steady state despite changing conditionsAbility to maintain a steady state despite changing conditions Water is important to this process because:Water is important to this process because: a. Makes a good insulator b. Resists temperature change c. Universal solvent d. Coolant e. Ice protects against temperature extremes

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 Measure of the concentration of H + ions Ranges from 0 – 14 pH of 7 is neutral (water) pH 0 – 6.99 is acid … H + pH 7.01 – 14 is basic… OH -

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. Will neutralize the substanceWeak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH. Will neutralize the substance Weak Acid Weak Base

Questions? I will not sleep through my education. I will not sleep… --Bart Simpson