CHM 101 Sinex1Acids and BasesPGCC CHM 101 SinexGeneral propertiesACIDS• Taste sour• Turn litmus• React with active metals – Fe, Zn• React with basesBASES• Taste bitter• Turn litmus• Feel soapy or slippery (react with fats to make soap)• React with acidsblue to red red to blueDefinitions• Acids – produce H+• Bases - produce OH-• Acids – donate H+• Bases – accept H+• Acids – accept e-pair• Bases – donate e-pair ArreheniusBronsted-LowryLewisonly in waterany solventused in organic chemistry,wider range of substancesExamplesArrheniusBronsted-LowryLewisHClNaOHHCl NH3:NH3BF3HCNThe hydrogen ion in aqueous solutionH++ H2O à H3O+ (hydronium ion)The Bronsted-Lowry ConceptConjugate pairsHCl Cl-CH3COOH CH3COO-NH4+NH3HNO3NO3-How does a conjugate pair differ?H+transferNeutralizationIn general: Acid + Base à Salt + WaterAll neutralization reactions are double displacement reactions.HCl + NaOH à NaCl + HOHHCl + Mg(OH)2àH2SO4+ NaHCO3àCHM 101 Sinex2H2O D H++ OH-Does pure water conduct electrical current?(H+)(OH-) = 10-14For pure water: (H+) = (OH-) = 10-7MThis is neutrality and at 25oC is a pH = 7.Water is a very, very, very weak electrolyte.How are (H+) and (OH-) related?waterHALet’s examine the behavior of an acid, HA, in aqueous solution.What happens to the HA molecules in solution?HAH+A-Strong Acid100% dissociation of HAWould the solution be conductive?HAH+A-Weak AcidPartial dissociation of HAWould the solution be conductive?HAH+A-Weak AcidHA D H++ A-At any one time, only a fraction of the molecules are dissociated.Strong and Weak Acids/BasesStrong acids/bases – 100% dissociation into ionsHCl NaOHHNO3KOHH2SO4Weak acids/bases – partial dissociation, both ions and moleculesCH3COOH NH3CHM 101 Sinex3pH2 3 4 5 6 7 8 9 10 11 12neutral @ 25oC(H+) = (OH-)distilled wateracidic(H+) > (OH-)basic or alkaline(H+) < (OH-)natural waters pH = 6.5 - 8.5normal rain (CO2)pH = 5.3 – 5.7acid rain (NOx, SOx)pH of 4.2 - 4.4 in Washington DC area0-14 scale for the chemistsfish populationsdrop off pH < 6 and to zero pH < 5You are here!http://nadp.sws.uiuc.edu/isoplethspH of Rainwateracross United States in 2001Increasing acidityWhy is the eastern US more acidic?What is acid rain?CO2(g) + H2O D H2CO3D H++ HCO3-Dissolved carbon dioxide lowers the pHAtmospheric pollutants from combustionNO, NO2+ H2O … à HNO3SO2, SO3+ H2O … à H2SO4bothstrong acidspH < 5.3105Db107BhBehavior of oxides in water– Group Abasic amphoteric acidic3A 4A 5A 6A 7A1A2A8AGroup Bbasic: Na2O + H2O à 2NaOH(O-2+ H2O à 2OH-)acidic: CO2+ H2O à H2CO3When life goes either wayamphoteric (amphiprotic) substancesHCO3-H2CO3CO3-2+ H+- H+Acting like a baseActing like an acidaccepts H+donates H+pH1 2 3 4 5 6 8 9 10 11The biological view in the human bodygastric juicevaginal fluidurinesalivacerebrospinal fluidbloodpancreatic juicebileacidic basic/alkaline7Tortora & Grabowski, Prin. of Anatomy & Physiology, 10thed., Wiley (2003)CHM 101 Sinex4Does the pH influence the activity of an enzyme?Trypsin is a digestive enzyme. Where?Intestinal pH range 7.0-8.5The amino acid glycine - amphotericIt’s an acid and a base! Loss of H+Gain of H+H2N-CH2-COOHH3N+-CH2-COOH H2N-CH2-COO-Chime structureThe amino acid glycine - Zwitterion formation Transfer of H+ from carboxylic acid group to amine group.H2N-CH2-COOHH3N+-CH2-COO-+-A dipolar ion forms.intramolecular acid-base reactionChime structureShow how water can be amphoteric.H2O+ H+- H+Dilutionwater (solvent) soluteconcentrated, Minitialdiluted, Mfinaladding water lowers the solute concentrationmoles of solute remain constantVinitialVfinalmolesinitial= molesfinalMfinalx Vfinal= Minitialx VinitialTitration CalculationHCl + NaOH à NaCl + HOHat equivalence point: moleHCl= moleNaOHmoles = M x VLMacidx Vinitial acid= Mbasex VburetA way to analyze