Module_2_files/Titration curves.ppt

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Neutralization of Acids and Bases

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In general, a titration involves the addition of either a strong acid, strong base or both (must go to completion) as follows: ACID + BASE WATER + SALT Titrations do not always yield an equivalence point with a pH of 7. Why? Can further hydrolyze to form acidic or basic solutions

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TitrationsStandard SolutionSample SolutionBuretteUnknown [ ] Sample SolutionKnown [ ] Standard Solution2nd titration?

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Why a primary standard?If NaOH is the standard solution, it’s [ ] may not be accurate. Why? NaOH is hygroscopic (absorbs moisture in the air) which can affect its molar mass A primary standard is used to verify the [ ] of the “known” standard solution A primary standard must be: Pure & stable Non-hygroscopic Have an accurately known molar mass

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Choosing Indicators For Titrationswill depend on the overall pH of the salt producedyellowblue

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Strong Acids and Strong Base TitrationsExample: HCl (strong acid) and NaOH (strong base) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________HCl + NaOH  H2O + NaClH+ + Cl- + Na+ + OH-  H2O + Na+ + Cl-H+ + OH-  H2OpH = 7 (neutral salt)Bromothymol blue

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Titration Curve for Strong Acid & Strong Base pH of sample solution is very low SABase is the standard solution being added

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Example: CH3COOH (weak acid) and NaOH (strong base) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________Weak Acids and Strong Base Titrations

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Weak Acid & Strong BasepH starts higher as CH3COOH is a weaker acidE.P > 7

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Weak Base and Strong Acid TitrationsExample: NH3 (weak base) and HCl (strong acid) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________

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Weak Base & Strong AcidStandard Acid is addedSample of Strong Base E.P < 7

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Three types of Titrations:

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Monoprotic AcidsWhen the mole ratio of acid to bases is 1:1 in the balanced equation (assuming that the concns are the same), then they will require equal volumes to reach equivalence pointAcid and Base strength is irrelevant!!Example: A 0.2 M strong acid requires an equal volume of 0.2 M weak base to reach equivalence point if they have 1:1 ratio

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Polyprotic AcidsWhen an acid releases more than one proton, ie. H2SO4, then they will require twice the volume of base to reach equivalence point

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Titration of a polyprotic acid: one equivalence point per acidic hydrogen

Last Updated: 8th March 2018