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Lecture

Chemistry II.docx

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Department
Chemistry
Course
CHEM 1AA3
Professor
Dr.Locke
Semester
Winter

Description
Lecture 1 Intro to Chem IILecture 2 Acidbase review Refer to chem I notesStrong acidsHCl HBr HI HClO HNO HSO4324Strong basesGroup 1 and group 2 hydroxides many group 2 are slightly solublesolubleHydrides HNaHH2ONaOHH22Oxides ONaOHONa2OH22Lecture 3 4 5 6 7 8 AcidbaseEg KOHHNOKNOHO22 2Assuming KOH is in excessSolution is a mixture of strong and weak basepH is determined only by strong baseWeak base contributes a small amount because of a low amount of dissociation and Le Chatelie strong base causes weak base equilibrium shifts equilibriumAssuming stoichiometric equivalent amounts of acid and baseSolution is only weak basepH determined by weak baseacid equilibrium KbAssuming HNO is in excess2Solution is a mixture of weak base and weak acid bufferBuffersSimilar and appreciable quantities of weak acid and weak base conjugatesAt half equivalence buffers resist changes in pH does not prevent changes in pHTitrationsEquivalence pointPoint in a titration when the moles titrant added and moles analyte are stoichiometrically equalHalf equivalence pointPoint in a titration when half of the moles of analyte has reacted with the titrant In weak baseacid titrations conjugate acidconjugate baseKaHAHAKaHpKapHStrong acid strong base Produces neutral salt at EP pH7Weak acid strong baseProduces basic salt at EP pH7Weak base strong acidProduces acidic salt at EP pH7 Hendersonhasselbalch equationBasepHpKlogaAcidConcentrations are at equilibrium of a mixture of conjugate pairsEquivalence point is theoreticalEnd points can actually be observedIndicatorsAre weak acidsbasesColour change occurs over 2 pH unitsColour of indicator depends on pHHInaqH2OlH3Oaq Inaqacid colourbase colourAccording to the Hendersonhasselblach equation the optimal colour change range is when pHsolutionpKaIndicatorOnly add a very small amount concentration of indicator to prevent interference with pHColour changeAcid colourpHpKHIn110 fold excess of HInbase colourpHpKHIn110fold excess of InPick an indicator with a pKa pKHIn close to expect equivalence point pH of the titrationIndictor only changes colour at the end point not necessarily at equivalence pointImportance of buffersBlood buffersBiochemical assaysLakes and streamsCommon ion effectIn an equilibrium ABCAdding in B or starting out with B will shift equilibrium to left and decreasesionizationEg if A is an acid then pH increases andionization decreases Buffer chemistryEquilibrium reaction of either weak species with water eg NHNH34The equation for a buffer is either the weak acid or base dissociation equilibrium Solution of weak acidbase conjugate pair and both concentrations 100xKaBuffer range and capacityweakbase0110weakacidBest capacity to resist changes from addition of acid or base when weak acid and weak base are large and equalEffective range pKa1Making a buffer
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