WaterReferenceLife and WaterA Polar MoleculeHydrogen bonds: bonds between moleculesWater is an excellent SolventSolubility of non-polar compoundsIonization of waterAcidity increases as pH decreasesIce, water as a solidSpecific Heat –melting & boilingLosses and Gains of WaterThe Earth’s Water CycleWater Balance in ChicagolandQuantities of WaterResidence TimeWater in airGroundwaterThe Great LakesVocabularyUIC UIC BioSBioS 101 Nyberg101 Nyberg11Lecture 5 Exam 1Lecture 5 Exam 1WaterWaterAll life is based on water. All actively growing living things are more than 50% water by weight.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg22ReferenceReference•• Assigned ReadingAssigned Reading–– In addition to chapter 2 pp 22In addition to chapter 2 pp 22--26, page 1095 26, page 1095 describes the global water cycle.describes the global water cycle.•• Fresh WaterFresh Water by E.C. by E.C. PielouPielou, 1998, University , 1998, University of Chicago Press is an excellent source of of Chicago Press is an excellent source of information about water.information about water.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg33Life and WaterLife and Water• Water is intimately involved in biological function at all levels from cellular reactions to the ecosystem.• Macromolecules behave/orient largely based on their attraction to or repulsion of (Hydrophilic versus hydrophobic) water• The vegetation of the terrestrial world is determined mostly by water availability.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg44A A PolarPolar MoleculeMolecule•• Water = HWater = H22 O = HO = H--OO--H = 3D viewH = 3D view•• The electrons in the bond are not shared The electrons in the bond are not shared equallyequally. The oxygen atom has a partial negative . The oxygen atom has a partial negative electrical charge and both hydrogen atoms have electrical charge and both hydrogen atoms have a partial positive charge. a partial positive charge. •• Molecules with separation of electrical charge Molecules with separation of electrical charge are said to be are said to be ‘‘polarpolar’’ molecules.molecules.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg55Hydrogen bondsHydrogen bonds: : bonds between moleculesbonds between molecules•• The positive charge on The positive charge on HH of one water of one water molecule molecule ‘‘bondsbonds’’ to the negative charge to the negative charge on on OO of different molecule. This attraction of different molecule. This attraction between water molecules is known as a between water molecules is known as a hydrogen bond..•• The hydrogen bond is much weaker than The hydrogen bond is much weaker than a covalent bond.a covalent bond.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg66Water is an excellent SolventWater is an excellent Solvent• Solvents allow materials (named solute) to mix completely (=dissolve).• Ionic compounds, such as salt, almost always are soluble in water.• Polar molecules typically readily dissolve in water.• Non-polar molecules dissolve only slightly in water.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg77Solubility of non-polar compounds• Oxygen: only a small amount dissolves in water, saturation is about 16 x 10-3g•l-1. More oxygen dissolves in cold water than in warm water.• Carbon dioxide dissolves well in water and forms carbonic acid, H2 CO3 . • Nitrogen, N2 , is less soluble than oxygen.• PCB and DDT are non-polar organic pollutants are only very slightly soluble in water, i.e. measured in ppb, parts per billion, 109.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg88Ionization of waterIonization of water•• The water molecule, HThe water molecule, H--OO--H, has a small probability of H, has a small probability of breaking into two pieces, Hbreaking into two pieces, H+ (the(the hydrogen ionhydrogen ion) and ) and OHOH- (the(the hydroxyl ionhydroxyl ion). ). •• The product of the molar concentration of hydrogen The product of the molar concentration of hydrogen ions and hydroxyl ions is always 10ions and hydroxyl ions is always 10-14..[H[H+]]••[OH[OH--] = 10] = 10-14..•• The The pHpH is is ––(log [molar hydrogen ion concentration]).(log [molar hydrogen ion concentration]).•• The pH of pure water is 7The pH of pure water is 7 as the concentrations of as the concentrations of hydrogen and hydroxyl ions must be equal.hydrogen and hydroxyl ions must be equal.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg99Acidity increases as Acidity increases as pHpH decreasesdecreases•• AcidityAcidity promotes many chemical reactions.promotes many chemical reactions.•• Substances that increase the concentration of Substances that increase the concentration of hydrogen ions are called hydrogen ions are called acidsacids..•• Your stomach is very acidic, pH = 1.5Your stomach is very acidic, pH = 1.5–– [OH[OH--] is 10] is 10-12.5 M as product of 10M as product of 10-1.5& 10& 10-12.5 =10=10-14..•• Carbon dioxide in atmosphere dissolves in rain Carbon dioxide in atmosphere dissolves in rain giving it a pH of giving it a pH of 5.65.6. Other gases (e.g. SO. Other gases (e.g. SO2 , , NNx OO) in air make the rain even more acidic.) in air make the rain even more acidic.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg1010Ice, water as a solidIce, water as a solid• One unusual property of water is that the solid form (ice) is less dense (Density is mass per unit volume) than as a liquid.• The fact that ice floats (ice is 11% less dense than 4° C water) is important in understanding the aquatic environment.– If ice was more dense than water, deep lakes (in this part of the world) would have ice at the bottom all year long.Lecture 5 Exam 1Lecture 5 Exam 1UIC UIC BioSBioS 101 Nyberg101 Nyberg1111Specific Heat Specific Heat ––melting & boilingmelting & boiling• At phase transitions adding heat does not raise temperature.•• Transition from ice to water takes a lot of energy Transition from ice to water takes a lot of energy without changing the 0without changing the 0°° temperature.temperature.–– MeltingMelting takes 80 calories per gram with no temp change.takes 80 calories per gram with no temp change.•• Transition from liquid water to water vapor