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09Post - From last week This week Concepts Strong/Weak...

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11/2/2011 1 Strength of Vinegar by Acid Acid-Base Titration Base Titration Final Exercise Final Exercise – 105 points 105 points 1 Last Update: 11/2/2011 11:35 AM Concepts: Strong/Weak Acids Acid Dissociation/K a Concentration End point / Equivalence point Titration curves Logarithms Indicator Mole Relationships pH & pK a Titration Techniques: Primary Standard This week Titration pH Measurement Apparatus: Burets pH Meter Weighing by Difference Preparing precise solutions Standardization Volumetric Flask Analytical Balance Pipet 2 Last exercise involved acid-base titration in which concentration of NaOH was given. In this exercise, you STANDARDIZE the NaOH. Standardization Analytical determination of purity or concentration of substance through reaction with substance of verified potassium hydrogen phthalate (KHP KHP) composition and purity ( Primary Standard ) This STANDARDIZATION involves reaction of NaOH with a PRIMARY STANDARD, the weak acid: O O H O O - 3 K + KHP is a monoprotic weak acid. One available proton. H C 8 H 4 O 4 - + OH - C 8 H 4 O 4 = + H 2 O + [K + ] The stoichiometry of the reaction is: 1 mol KHP 1 mol NaOH STOICHIOMETRY pK a is is 5.4 5.4 Acetic acid, CH 3 COOH , is also a monoprotic weak acid. 1 mol CH 3 COOH 1 mol NaOH CH 3 COOH + OH - CH 3 COO - + H 2 O It’s pK a is 4.7 4 H pK a = 4.7 pH ~ 8.5 pH mL of NaOH added pK a 5 It does not matter in which order you A.) Standardize NaOH, B.) Titrate Unknown C.) Determine pH of unknown PROCEDURE A. STANDARDIZATION Prepare solution of known concentration of primary standard, KHP Weigh sample BY DIFFERENCE * Dissolve fully in ERLENMEYER Bring to total volume in VOLUMETRIC FLASK** Must transfer ALL the solution *Web supplement ** **Follow manual procedure Follow manual procedure 6
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