Analysis of Vinegar by Titration
...ark with NaOH and the experiment continued. 2. The Pipette and the Vinegar: Johnson 2 Using a 5 mL volumetric pipette, 5.0 mL of non-specific commercial vinegar was dispensed into a 100 mL Erlenmeyer flask. (The first voiding was incorrectly performed and both the flask and pipette had to be emptied and re-filled). Next, using a 50.0 mL graduated cylinder, 10.0 mL of tap water (the procedure called for distilled water) was added to the vinegar in the flask. Finally, five to six drops of Phenolphthalein indicator (the procedure called for three) were added to the vinegar and water solution. 3. The Reaction: The stopcock of the buret was then opened to very slowly to allow the NaOH to trickle into the prepared vinegar, water, and indicator solution. As the NaOH solution dropped to around the 17.0 mL mark on the buret, temporary flashes of a pink color began to be seen. These would quickly vanish, however, with a little swirling of the flask. Somewhere between the 18.0-20.0 mL marks, the entire sample became a violent, dark pink. Apparently, the sample had been over-titrated. Steps #1, #2, and #3 had to be re-performed to the same point in order to continue with the first trial. Following the correction, a final, permanently pink color appeared at the 20.8 mL mark on the buret. The reading from the Buret was then recorded. C. The Second/Final Trial 1. The Buret and the NaOH: The previously used 50.0 mL buret was again rinsed with about 20.0 mL of 0.2170 M NaOH solution re-clamped to the ring stand. The NaOH was then poured into the buret up to the 49.2 mL mark. 2. The Pipette and the Vinegar: For a second time, a 5 mL volumetric pipette was filled with commercial vinegar dispensed into a 100 mL Erlenmeyer flask. Next, using a 50 mL graduated cylinder, 10 mL of distilled water (the source of water corrected during the second trial) was added to the flask. Finally, three drops of Phenolphthalein indicator were again added to the flask. Johnson 3 3. The Reaction: The stopcock of the buret was then opened slowly to allow the NaOH to trickle into the prepared vinegar, water, and indicator solution. A pink color began to appear as the solution in the buret dropped to the 17.0 mL mark, and remained permanently pink at the 20.1 mL mark. This data was then recorded. II. Observed Experimental Data: Trial #1 Trial #2 Molarity of NaOH Solution (M) 0.2170 M 0.2170 M Initial Reading of NaOH in Buret (mL) 49.4 mL 49.2 mL Final Reading of NaOH in Buret (mL) 20.8 mL 20.1 mL IV. Sample Calculation(s): A. Volume of NaOH Used in Titration (Initial Reading of NaOH in buret) - (Final reading of NaOH in buret) = Volume of NaOH used in titration: 49.4 mL NaOH – 20.8 mL NaOH = 28.6 mL NaOH B. Molarity of Acetic Acid in Vinegar (Volume of NaOH used in titration ÷ Volume vinegar in sample) x (Molarity of NaOH solution) = Molarity of acetic acid in vinegar: Johnson 4 (28.6 mL NaOH ÷ 5.0 mL Vinegar) x 0.2170 M NaOH = 0.9270 M CH³CO²H C. Average Molarity of Acetic Acid (Molarity acetic acid in Trial #1 + Molarity of acetic acid in Trial #2) ÷ 2 = Average molarity of acetic acid: 0.9027 M CH³CO²H + 1.2629 M CH³CO²H = 2.1656 M ...