Indicators_expt - Chemistry 20L Revised Procedures for...

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Chemistry 20L 1 Revised Procedures for Assignment #4 - Titrations & Indicators (i) Read pages 56-58 in the lab manual for the introduction and background of the experiment (ii) Pre-lab study questions for this experiment may be found on pages 58-59 in the lab manual. Use the following revised procedures when writing your reports. At the beginning of the lab period, your TA will divide the class into pairs. If the class has an odd number of students, one person will be assigned to work alone. In this assignment, your group will determine and compare the calculated concentration of a sulfuric acid solution based on the results obtained from experimental end points using three different indicators and a pH meter. The titrations will be performed using a standard base and a sulfuric acid solution with an unknown concentration. The three different acid/base indicators that your group will use in this assignment are: Bromocresol Green, Methyl Orange, and Phenolphthalein The standard base used in this assignment is called 2-amino-2(hydroxymethyl)-1,3-propanediol. It has a molecular formula of (HOCH 2 ) 3 CNH 2 . We will condense the formula for this base to RNH 2 from this point on. RNH 2 is a weak primary amine base, an organic derivative of ammonia. In solution, the nitrogen atom in the base reacts with an acid as follows: H + (aq) + (HOCH 2 ) 3 CNH 2 (aq) = (HOCH 2 ) 3 CNH 3 + (aq) Procedure: Obtain about 100 mL of the sulfuric acid solution in a clean, dry 250-mL Erlenmeyer flask. Label this flask as “Sulfuric Acid”. Obtain about 50 mL of the RNH 2 standard base solution in a clean, dry 150-mL beaker. Label the beaker as “Standard Base”.
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This note was uploaded on 04/24/2008 for the course CHEM 20L taught by Professor Gould during the Spring '08 term at UCLA.

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Indicators_expt - Chemistry 20L Revised Procedures for...

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