CH204 Expt 4 sp10 - 2/19/2010 This Week: Acid-Base...

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2/19/2010 1 1 Experiment 4 Acid Experiment 4 Acid-Base Titration Base Titration 2 This Week: Acid-Base Titrations Acid + Base Salt + H 2 O unknown known h A titration is a method we will use to determine the concentration of an unknown acid. h We will measure the volume of a known concentration of a base that is required to react with a volume of an acid with an unknown concentration. h We will use an indicator in the acid solution to indicate when to stop the titration. 3 Acid-Base Titrations h An indicator is a substance that is able to change colors depending on the [H + ] in the solution. h When all of the [H + ] = [OH ± ] in a titration, the equivalence point has been reached. c No excess hydrogen ions or hydroxide ions exist in the reaction mixture. h When the color changes during a titration, the endpoint has been reached and the titration is stopped. c Ideally, the endpoint is the same as the equivalence point, but it depends on how close the color change of the indicator is to the actual equivalence point. c Most of the time, the endpoint is either slightly higher or slightly lower than the actual equivalence point. 4 Titration Setup Burette containing known [NaOH] . (The titrant or secondary standard .) Erlenmeyer flask containing acid sample , water , and two drops of phenolphthalein . Read all volumes to 0.01 mL! 5 Phenolphthalein (Indicator) Colorless below pH 8.2 Pink above pH 8.2 6 Acid Acid-Base Indicators Base Indicators Equivalence point pH = 7 Endpoint pH = 8.2
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2/19/2010 2 7 Standardizing the Standard Base Solution h Standardization is the process of determining the concentration of the titrant (NaOH) with a know amount of a primary standard (KHP) . This is necessary because NaOH pellets are not pure. KHP. Potassium Hydrogen Phthalate. C 8 H 5 O 4 K 8 KHP 9 Acid-Base Titration with KHP Before endpoint At endpoint Overshoot endpoint At the endpoint, the pink color should be very, very faint. 10 Experiment 4 Overview PART 1: STANDARDIZATION OF NaOH Weigh out about 7 grams of NaOH pellets, you cannot reasonably weigh it to 0.0001 g. Record this value.
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This note was uploaded on 03/17/2010 for the course CH 204 taught by Professor Leytner during the Spring '08 term at University of Texas at Austin.

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CH204 Expt 4 sp10 - 2/19/2010 This Week: Acid-Base...

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