PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Chapter 4 WATER Most abundance substance in living systemsView of Earth from SpaceWill be tested on entire chapterPractice solving problemsPage 97 box 4-2Page 103 box 4-3Water Not just a solvent in which reactions are performed in a living cell Is a reactant or a product in several reactionsHydrolysis reactionOxidation of fuelsC6H12O6 + 6O2 6CO2 + 6H2OGlucosePhysical and Chemical Properties of Water Read pages 82 - 94Structure of the water moleculeDipolar nature of the water molecule is shown hereMore electronegativeHydrogen bonding in iceCommon hydrogen bonds in biological systemsUsually oxygen or nitrogenSome biologically important hydrogen bondsCompounds that dissolve in water(hydrophilic)Compounds that dissolve in solvents such as chloroform(hydrophobic)NaCl crystal lattice is disrupted as water molecules cluster around sodium and chloride ions G = H – T SSNaCl crystal Hydrated ionsAmphipathic compounds in aqueous solutionPolar head groupHydrophillicNon-polar HydrophobictailStable structure of amphiphatic compounds in water are called micellesWeak interactions are crucial to macromolecular structure & functionH2O H+ + OH-[H+] [OH-] [H2O]Keq =Ionization of water is expressed by an equilibrium constantKw[H+] [OH-] =At 25 oC [H2O] = 55.5 MKeq= 1.8 x 10-16 M[H+] [OH-] [H2O] Keq =KwEquilibrium constantIonic product of water at 25 oC G of water in 1 L Molecular weight of water [H2O] =Kw[H+] [OH-] =At neutral pH [H+] = [OH- ]Kw[H+] [H+] = = [H+]2[H+] = Kw1 x 10-14 M2=[H+] = [OH-] = 10-7 M- log [H+] = - log 10-7 MpH = 7Neutral solution pH is 7Not an arbitrary numberDerived from ionic product of waterpH of some aqueous fluidspH optima of some enzymesWhy is pH important?BuffersAqueous systems that resist changes in pH when small amounts of acid (H+) or base (OH-) are addedBuffer system consists of weak acid and its conjugate baseCH3COOH CH3COO- + H+ Weak acids and bases have characteristic dissociation constantsHA A- + H+ Keq = [A-] [H+] [HA]= KaDissociation constantpKa = - log Ka = logKa Stronger the acid Higher the Ka Lower the pKa1Conjugate acid-base pairs consist of a proton donor and a proton acceptorTitration curve of acetic acidStrong AcidWeak AcidComparison of the titration curves of 3 weak acidsThe acetic acid – acetate pair as a buffer systemHenderson-Hasselbalch EquationAt midpoint of the titration [A-] = [HA]Then pH =
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