ANALYSIS OF VINEGAR VIA TITRATION PAGE 1 Name: Jane Student Title: Analysis of Vinegar via Titration Date: 08/15/2000 Purpose: In this experiment the molar concentration and mass percent concentration of acetic acid, HC2H3O2(aq), in a vinegar solution were determined via titration using a standard solution of sodium hydroxide, NaOH(aq). Procedure: A sample of vinegar was analyzed, and its brand and mass percentage of acetic acid were recorded. Using a 10.00-mL pipet, 10-mL portions of the vinegar were delivered to each of three Erlenmeyer flasks, and a few drops of phenolphthalein indicator were added to each flask. About 150 mL of a standard sodium hydroxide solution, NaOH (aq) was obtained for the titrations. The initial and final buret readings were recorded as the two vinegar solutions were each titrated to a phenolphthalein endpoint. The volume of NaOH required to titrate each vinegar sample was determined and used to calculate the molar concentration of HC2H3O2(aq) in each vinegar sample. The average molar concentration of HC2H3O2(aq) for the two trials was determined along with the average molar concentration and the percent difference. If the two trials did not agree within 1%, additional trials were carried until two or more trials agreed within 1%. The density of the vinegar solution was determined using "weighing by difference" and the volume of vinegar in a graduated cylinder. The average molarity of HC2H3O2(aq) and the density of the vinegar solution were then used to calculate the mass percent concentration of HC2H3O2(aq) in the vinegar. Finally, the experimentally determined mass percent concentration of HC2H3O2(aq) was compared with the mass percent concentration reported by the manufacturer. Data: Molarity of standard NaOH(aq): 0.2165M Vinegar brand: Smiths Reported mass percent of HC2H3O2 in vinegar: 5.0% Table 1: Vinegar Titration Trial 1 Trial 2 Trial 3 Volume of vinegar used 10.00 mL 10.00 mL 10.00 mL Initial Volume of NaOH 0.00 mL 0.15 mL 0. 35mL Final Volume of NaOH 39.30 mL 38.80 mL 39.05 mL Volume of NaOH used 39.30 mL* 38.65 mL 38.70 mL *In Trial 1 NaOH solution was added past the endpoint, leading to an incorrectly high volume of NaOH. Density of vinegar solution: Mass of Empty 10-mL Graduated Cylinder: 15.1256 g Mass of Graduated Cylinder + vinegar: 25.1753 g Mass of vinegar: 10.0503 g Volume of vinegar used: 10.00 mLANALYSIS OF VINEGAR VIA TITRATION PAGE 2 Calculations: Molarity of HC2H3O2 in vinegar: Trial 1: 232232OHHC 0.8508ML 0.010001NaOH mol 1OHHC mol 1LNaOH mol 0.2165 NaOH L 0.03930 =××× Trial 2: 232232OHHC M 0.8368L 0.010001NaOH mol 1OHHC mol 1LNaOH mol 0.2165 NaOH L 0.03865 =××× Average [HC2H3O2] for Trials 1 and 2 = 0.8438M20.8368M 0.8508M=+ % difference for [HC2H3O2] for Trials 1 and 2 = 1.66% 100%0.8438M 0.0140M100%0.8438M|0.8368M 0.8508M|=×=×− Trial 3: 232232OHHC M 0.8379L 0.010001NaOH mol 1OHHC mol 1LNaOH mol 0.2165 NaOH L 0.03870 =××× Average [HC2H3O2] for Trials 2 and 3 only = 0.8374M20.8379M 0.8368M=+ % difference for [HC2H3O2] for Trials 2 and 3 = 0.13% 100%0.8474M 0.0011M100%0.8374M|0.8379M 0.8368M|=×=×− Density of vinegar: density = g/mL 005.1mL 10.00g 10.0503volumemass== Mass percent of HC2H3O2 in vinegar: 5.063%100%solution g 1.005solution mL3O2H2HC mol 3O2H2HC g 60.052solution mL 10003O2H2HC mol 0.8474=××× % difference for Mass Percent Concentration = 2% 100%5% 0.1%100%5.0%|5.0% - 5.063%|=×=×ANALYSIS OF VINEGAR VIA TITRATION PAGE 3 Results: Table 2: Vinegar Titration Results Trial 1 Trial 2 Trial 3 Molarity of HC2H3O2(aq) in vinegar 0.8508M 0.8368M 0.8379M Average Molarity of HC2H3O2(aq) 0.8374M (using only Trials 2 and 3)* Percent Difference 0.13% (for Trials 2 and 3 only)* Mass percent concentration of HC2H3O2(aq) 5.063% Discussion: In this experiment, a sample of Smiths brand vinegar was analyzed via titration with a standard 0.2165M NaOH solution. Three trials were carried out to achieve the required precision of less than 1% difference. The calculated molar concentrations of acetic acid for the first two trials were 0.8508M and 0.8368M, so the percent difference was 1.66%; thus, a third trial was conducted. The calculated molar concentration of acetic acid for trial #3 was 0.8379M, which had a 0.13% difference compared to trial #2. Thus, only the data from these trials were used to calculate the average molar concentration of acetic acid of 0.8374M and the resulting mass percent concentration of the acetic acid in the vinegar of 5.063%. This gave a 2% difference compared to the 5.0% concentration reported on the bottle of the Smith’s brand vinegar. One possible source of error and reason for the difference between trial 1 and the other trials was the addition of NaOH solution in a continuous stream near the endpoint, so the solution was a dark pink color at the end for trial #1. Because trial #1 required 0.55-0.6 mL more NaOH solution than trials #2 and #3, the volume of NaOH used for this trial was too high, resulting in an incorrectly high calculated molarity for acetic acid. Another possible source of error would be losing some vinegar when transferring the solution from the pipet to the Erlenmeyer flask. The lower volume of vinegar would result in a lower volume of NaOH required to titrate it to a phenolphthalein endpoint, so assuming the volume of vinegar transferred was still taken to be 10.00 mL, the resulting calculated molar concentration of acetic acid would be incorrectly low. Yet another source of error would be recording an incorrect initial volume of NaOH solution, such as recording the initial volume as 0.00 mL if the level of solution was actually higher than the 0.00 mL on the buret. The excess NaOH solution above the 0.00 mL mark would result in more NaOH solution delivered than is actually recorded based on the endpoint. Because an incorrectly low volume of NaOH delivered will be recorded, the resulting calculated molar concentration of acetic acid will be incorrectly low as well. Thus, correct technique is essential for obtaining good data and accurate and precise results in this experiment. Conclusions: In this experiment, a sample of Smiths brand vinegar was analyzed via titration with a standard 0.2165M NaOH solution. The vinegar’s molar concentration was determined to be 0.8374M, and its mass percent concentration of acetic acid was