2 Properties of Water Polar molecule Cohesion and adhesion High specific heatDensity – greatest at 4oCUniversal solvent of life
3 Polarity of WaterIn a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Gives water more structure than other liquidsBecause oxygen is more electronegative, the region around oxygen has a partial negative charge.The region near the two hydrogen atoms has a partial positive charge.A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.2 corners are orbitals with unshared electrons and a weak negative charge2 are occupied by hydrogen atoms that have polar covalent bonds
5 HYDROGEN BONDSExtraordinary Properties that are a result of hydrogen bonds.Cohesive behaviorResists changes in temperatureHigh heat of vaporizationExpands when it freezesVersatile solventHold water molecules togetherEach water molecule can form a maximum of 4 hydrogen bondsThe hydrogen bonds joining water molecules are weak, about 1/20th as strong as covalent bonds.They form, break, and reform with great frequency
6 Organisms Depend on Cohesion Hydrogen bonds hold the substance together, a phenomenon called cohesionCohesion is responsible for the transport of the water column in plantsCohesion among water molecules plays a key role in the transport of water against gravity in plantsAdhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.
8 Moderates Temperatures on Earth Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.Celsius Scale at Sea Level100oCWater boils37oCHuman body temperature23oCRoom temperature0oCWater freezesWhat is kinetic energy?Heat?Temperature?Calorie?What is the difference in cal and Cal?What is specific heat?
9 Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1oC.Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for:Prevention of temperature fluctuations that are outside the range suitable for life.Coastal areas having a mild climateA stable marine environment
10 Evaporative CoolingThe cooling of a surface occurs when the liquid evaporatesThis is responsible for:Moderating earth’s climateStabilizes temperature in aquatic ecosystemsPreventing organisms from overheating
11 Density of Water Most dense at 4oC Contracts until 4oC Expands from 4oC to 0oCThe density of water:Prevents water from freezing from the bottom up.Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation.Makes transition between season less abrupt.
13 Solvent for Life Solution Aqueous solution Hydrophilic Hydrophobic SolutesolventAqueous solutionHydrophilicIonic compounds dissolve in waterPolar molecules (generally) are water solubleHydrophobicNonpolar compounds
14 Most biochemical reactions involve solutes dissolved in water. There are two important quantitative proprieties of aqueous solutions.1. Concentration2. pH
15 Concentration of a Solution Molecular weight – sum of the weights of all atoms in a molecule (daltons)Mole – amount of a substance that has a mass in grams numerically equivalent to its molecular weight in daltons.Avogadro’s number – 6.02 X 1023A mole of one substance has the same number of molecules as a mole of any other substance.
16 Molarity Calculate a one molar solution of sucrose, C12H22O16. The concentration of a material in solution is called its molarity.A one molar solution has one mole of a substance dissolved in one liter of solvent, typically water.Calculate a one molar solution of sucrose, C12H22O16.C = 12 daltonsH = 1 daltonO = 16 daltons12 x12 = 1441 x 22 = 2216 x 11 = 176342For a 2M solution?For a .05 M solution?For a .2 M solution?
18 This reaction is reversible. A simpler way to view this process is that a water molecule dissociates into a hydrogen ion and a hydroxide ion:H2O <=> H+ + OH-This reaction is reversible.At equilibrium the concentration of water molecules greatly exceeds that of H+ and OH-.In pure water only one water molecule in every 554 million is dissociated.At equilibrium, the concentration of H+ or OH- is 10-7M (25°C) .Only a hydrogen ion is actually transferredThe transferred proton binds to an unshared orbital of the second water molecule.The water molecule that loses the proton
19 Acids and BasesAn acid is a substance that increases the hydrogen ion concentration in a solution.Any substance that reduces the hydrogen ion concentration in a solution is a base.Some bases reduce H+ directly by accepting hydrogen ions.Strong acids and bases complete dissociate in water.Weak acids and bases dissociate only partially and reversibly.There is only 1 molecule out of 554,000,000 water molecules that is dissociated.
20 pH Scale The pH scale in any aqueous solution : [ H+ ] [OH-] = 10-14Measures the degree of acidity (0 – 14)Most biologic fluids are in the pH range from 6 – 8Each pH unit represents a tenfold difference (scale is logarithmic)A small change in pH actually indicates a substantial change in H+ and OH- concentrations.
21 ProblemHow much greater is the [ H+ ] in a solution with pH 2 than in a solution with pH 6?Answer:pH of 2 = [ H+ ] of 1.0 x 10-2 = 1/100 MpH of 6 = [ H+ ] of 1.0 x 10-6 = 1/1,000,000 M10,000 times greater
22 Buffers A substance that eliminates large sudden changes in pH. Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life.Are combinations of H+ acceptors and donors forms in a solution of weak acids or basesWork by accepting H+ from solutions when they are in excess and by donating H+ when they have been depleted.
23 Acid PrecipitationRain, snow or fog with more strongly acidic than pH of 5.6West Virginia has recorded 1.5East Tennessee reported 4.2 in 2000Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphereLowers pH of soil which affects mineral solubility – decline of forestsLower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.
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