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Unformatted text preview: Arjun Rastogi 4 th Hour 3 /31 /08 Titration of a Diprotic Acid: Identifying an Unknown I Purpose: The purpose of this lab is to identify an unknown diprotic acid by finding its molecular weight. I I Procedure: Weigh out .12 grams of unknown diprotic acid and record the mass to the nearest . 001g in your data table. Transfer the unknown acid to a 250 mL beaker and dissolve in it in 100 mL of distilled water. CAUTION: handle solid acid with care. Acid can harm eyes, skin, and respiratory tract. Place the baker on a magnetic stirrer. Using a utility clamp, suspend a pH Sensor above the beaker. Position it so that the sensor is outside of the beaker so it will not hit the stirring bar. Turn on the magnetic stirrer to a medium stirring rate. Obtain 60 mL of .1 NaOH solution in a 250 mL beaker. Obtain a 50 mL buret and rinse the buret with a few mL of the .1 NaOH solution. Record the concentration of the NaOH in the data table. Using a utility clamp, attach the buret to the stand. Fill the buret with the NaOH soltion so that it is a little above the 0.00 mL line. Drain a small amount of NaOH so the buret tip is full of NaOH making sure that the solution level in the buret is now at 0.00 line. Connect the pH sensor to the computer interface and open the file 25a Titration Dip Acid from the Chemistry with Computers folder of Logger Pro 3.1. To begin titration follow these steps: a) Click collect on the computer and monitor the pH for 5-10 seconds. Once the pH has stabilized select keep. In the edit box, type 0 and press ENTER to store the first data pair for this experiment. The 0 represents the number of drops added. b) Add NaOH to the beaker until the pH has risen about .2 units. Once this is accomplished click keep. In the edit box, type the current buret reading to the nearest .01 mL and press ENTER. c) Continue to add NaOH in increments that raise the pH about .2 units and enter the buret reading after each addition. Proceed in this manner until the pH is 3.5 units. d) Once the pH reaches 3.5, switch to 2-drop increments entering the buret reading after each increment. e) After pH reaches 4.5 add larger increments to raise the pH by 2 units and enter the buret reading after each addition. Continue in this manner until a pH of 7.5 is reached. f) When pH reaches 7.5, change to 2-drop increments. Enter the buret reading after each increment. g) When pH reaches 10, add larger increments that raise the pH by .2 units. Enter the buret reading after each increment. When data collection has finished, click Stop. Dispose of the contents of the beaker and print a copy of the table. Repeat process again for trial 2. I I I Data Collection: T r iail 1 Mass of diprotic acid .122 g Concentration of NaOH .100 M (1) Equivalence point Second equivalence point (2) NaOH volume added before and after largest pH increase 21.3 mL before 21.5 mL after (3) Volume of NaOH added at equivalence point 21.4 mL (4) Moles of NaOH .00214 moles (5) Moles of diprotic acid H...
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This note was uploaded on 05/25/2010 for the course CHEM 101 taught by Professor Fricke during the Spring '10 term at Canisius College.
- Spring '10