CHE134 Summer Lecture 8

# CHE134 Summer - TITRATION OF SA AND ASA WITH NaOH pH vs VOLUME OF NaOH ADDED 14 a K p 12 10 8 6 4 2 0 10 20 30 40 pH 300 mg SA VOLUME OF ADDED NaOH

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IDENTIFICATION OF AN UNKNOWN WEAK ACID TEST EXERCISE (105 points) NaOH 2 4 6 8 10 12 14 pH 0 10 20 30 40 VOLUME OF ADDED NaOH TITRATION OF SA AND ASA WITH NaOH pH vs VOLUME OF NaOH ADDED 300 mg SA pKa EMM

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Purpose: To determine the molar mass and pKa and thereby determine the identity of an unknown acid by pH titration – Same technique as last week! Concepts: pH, pKa Nernst Equation Calibration and use of the pH meter Effective Molar Mass Titration Curve Stoichiometry Equivalence Point Techniques: Weighing by Difference Using a pH Meter Graphing Apparatus: pH Meter Buret
As usual, we seek to use about 25 ( 25 & 3) mL of NaOH to reach equivalence point WHY? Optimizes buret precision and produces an easily interpretable graph BUT Molar mass of the acid is unknown STEP 1: DETERMINE TITER of your acid mg of acid that will consume 1 mL of NaOH Everyone uses ~ 200 mg of acid – weighed out ACCURATELY into a 150 mL beaker. Titrate to phenolphthalein end-point - No pH METER

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e.g. IF 225.1 mg of your acid react with 18.46 mL of the NaOH, TITER of Your Acid = 225.1 mg / 18.46 mL = 12.19 mg / mL NaOH STEP 2. From TITER , calculate the weight of your acid that would consume 25 & 3 mL of NaOH e.g. WEIGHT = ( 25 3 mL ) x 12.19 mg / mL = 305 & 36 mg OF ACID STEP 3. Weigh out the computed amount of your acid on the ANALYTICAL BALANCE BY DIFFERENCE
STEP 4.

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## This note was uploaded on 01/09/2011 for the course CHE 134 taught by Professor Staff during the Summer '08 term at SUNY Stony Brook.

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CHE134 Summer - TITRATION OF SA AND ASA WITH NaOH pH vs VOLUME OF NaOH ADDED 14 a K p 12 10 8 6 4 2 0 10 20 30 40 pH 300 mg SA VOLUME OF ADDED NaOH

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