1 Experiment 12B: Analysis of Commercial Vinegars Chemistry 101 Section 0258 (M,W) 28 March 2016 Abstract Experiment 12B was conducted by a group of eight people. The purpose was to determine the acetic acid concentration of three different commercial vinegars by titrating with sodium hydroxide solution and then perform a cost analysis to see how acidic concentration relates to cost. The vinegars tested were: Kikkoman rice vinegar, Special Value white distilled vinegar, and Kroger apple cider vinegar. Through trials and calculations, our group concluded that Special Value white distilled vinegar was the best option according to acid concentration and cost analysis. Introduction Titration is a technique where a solution with a known concentration, the titrant, is used to determine the concentration of an unknown solution. The titrant in this experiment is 0.1 M sodium hydroxide, which is measured through a burette into the unknown diluted solution, in this case the acetic acid solution, until a reaction is complete. The chemical reaction in this experiment was: NaOH(aq) + HC​
H​
O​
(aq) → NaC​
H​
O​
+ H​
O 2​
3​
2​
2​
3​
2​
2​
where the acetic acid is neutralized by the base, sodium hydroxide. When titrating an acid and a base, neutralization occurs at the equivalence point, the point in which the acid and the base have an equal amount of moles. The pH indicator, phenolphthalein, signals the endpoint when the clear solution changes to pale pink that stays for at least thirty seconds. If the pale pink shade does not stay, it means the equivalence point has not been reached. However, if the solution 2 changes to bright pink, then the endpoint has been overshot and the trial should not be included in the data. In this experiment, we analyzed three different kinds of vinegars through the process of titration and determined their acetic acid concentrations. Acetic acid is produced by bacterial fermentation. Vinegar is a combination of 5% to 20% acetic acid, water, and chemicals that may include flavorings. We used Kikkoman rice vinegar which expired on 26 July 2014, Kroger apple cider vinegar which expired on 10 January 2011, and Special Value white distilled vinegar with an unknown expiration date. As a group, we hypothesized that if the vinegars expired, then the acetic acid concentration would decrease and that the vinegar with the higher percent of acetic acid would cost less per gram. The following formulas were applied to calculate the concentration of acetic acid in the different vinegars: Molarity = VMoles
olume
(1) M​
V​
= M​
V​
1​
1​
2​
2
(2) Experimental Our group of eight divided into three smaller groups each focusing on one type of vinegar while everyone conducted their own titration. Since we had already created a standardized base in Experiment 12A, we used the same sodium hydroxide solution for this experiment. The base solution was about 0.1M and too dilute to provide a satisfactory titration with commercial vinegar, so we used volumetric glassware to dilute each vinegar with deionized water. Once the acetic acid solutions were prepared, we each rinsed a burette with tap water, deionized water, and coated it with standardized sodium hydroxide solution. The burette was filled until the 0.0 mL mark with sodium hydroxide solution. With a pipette and bulb, we deposited 25.0 mL of acetic 3 acid solution into clean Erlenmeyer flasks for at least two trials. We added two drops of phenolphthalein to the solution to indicate the endpoint of the titration. The endpoint of the titration is determined by the change in color in the reaction flask. We recorded the initial and final volumes of the base in the burette. Finally, we determined the average volume of sodium hydroxide used for each vinegar and proceeded with the rest of the calculations. Results and Discussion As shown on Table 1 below, for each trial conducted, we used 0.1 M of sodium hydroxide as the titrant. Since there were three different vinegars for titration, there were at least four individual trials for each vinegar. For the breakdown of the calculations we took the average volume of sodium hydroxide used. We used the average volume along with formula (1) to find the molarity of acetic acid in the solution and formula (2) to determine the molarity of commercial vinegar. To calculate for acetic acid percent by mass and cost per gram of vinegar, we used dimensional analysis. For rice vinegar, we conducted a total of six trials using 0.1 M sodium hydroxide. As seen in Table 1, we found the average volume of sodium hydroxide used, which was 17.30 mL. The molarity of acetic acid was 0.00692, while the molarity of the commercial vinegar was 0.692, and the percent acetic acid was 4.2%. From the $1.19 cost per 10 fl oz, we found the cost per gram of rice vinegar was approximately 0.10 cents. The same calculations were performed for the white distilled vinegar and apple cider vinegar. Table 1: Acid­Base Titration Between NaOH and 3 Commercial Vinegars 4 Vinegars NaOH M Initial Vol. (mL) Final Vol. (mL) Average Volume NaOH Acetic Acid Acetic Acid (%) Cost ($)/g Molarity Commercial Vinegar Molarity Kikkoman Rice Vinegar 0.1 M 0.0 mL 17.30 mL 17. 30 mL 0.00692 M 0.692 M 4.2% $0.097/
g Special Value White Distilled Vinegar 0.1 M 0.0 mL 21.26 mL 21. 26 mL 0.08502 M 0.8502 M 5.1% $0.021/
g Kroger Apple Cider Vinegar 0.1 M 0.0 mL 21.00 mL 21. 00 mL 0.08399 M 0.8399 M 5.0% $0.083/ g The small groups that formed for each of the vinegars all had similar final readings. Our calculations proved that the Special Value white distilled vinegar has a 5.1% acidity even though it reports having a 4% acidity. The Kroger apple cider states an acidity of 5% and the Kikkoman rice vinegar states an acidity of 4.2%, both of which are correct according to our calculations. After calculating for cost per gram, the rice vinegar is about 0.10 cents, the white distilled vinegar is 0.02 cents, and the apple cider vinegar is 0.08 cents. Conclusion The purpose of experiment 12B was to determine the acetic acid concentration in the following vinegars: Kikkoman rice, Kroger apple cider, and Special Value white distilled and to compare the concentrations calculated to the concentrations listed on the bottles. Kikkoman claimed an acid percentage of 4.2%, Special Value was labeled 4%, and Kroger 5%. ​
The Kikkoman rice vinegar expired on 26 July 2014, the Kroger apple cider vinegar expired on 10 5 January 2011, and the Special Value white distilled vinegar had an unknown expiration date. ​
We hypothesized that after many years after expiration, the vinegars would lose their acidic concentration compared to an unexpired vinegar because water molecules in the air would slowly dilute the vinegars. After calculating and comparing concentrations, our hypothesis was proven wrong. The Kikkoman rice vinegar was calculated to have 4.2% acetic acid, the same amount that was labeled on the bottle. The same is to be said with the Kroger apple cider vinegar, with a 5.1% acetic acid concentration, which was also labeled on the bottle. The Special Value vinegar was the only one that had a different acidic concentration than it promoted on the bottle with a 4% concentration, when in fact, the group calculated 5%. It is most likely that the Special Value vinegar had a higher acidic percentage than labeled on the bottle because the manufacturer intended for their vinegar to be stronger and have a longer shelf life. We decided to research vinegar shelf life and found that white distilled vinegar has an indefinite shelf life as long as it is stored under the proper conditions. This disproves our hypothesis and shows that the expiration date on the vinegar bottles will most likely not affect the accuracy of our concentration calculations. Furthermore, part of the experiment was also a cost analysis for each vinegar. The most expensive vinegar through calculations for less acidity was the Kikkoman rice vinegar. This vinegar had an acid concentration of 4.2% and costs around 0.10 cents per gram. The Kroger apple cider was the second most expensive. This vinegar costs 0.08 cents per gram with an acid concentration of 5%. According to our calculations, the vinegar that will give you more bang for your buck is the Special Value white distilled vinegar. Not only does this vinegar have an 6 indefinite shelf life, it has an acid concentration of 5.1%, and it only cost less that 0.5 cents per gram. Based on the dollar per gram calculations we also concluded that Special value used the minimum amount of acetic acid per gram. We could also analyze that flavored vinegars are slightly more expensive than plain white distilled vinegars. We assume that consumers should buy white distilled vinegar since it is inexpensive and it has more acidic acid per gram. Possible experimental errors could include incorrectly calculating the amount of sodium hydroxide needed to make a 0.1M solution, not using the same sodium hydroxide for the same vinegars, not standardizing the base solution on the same day as we conducted experiment 12B, reading the burette the wrong way, and overshooting the endpoint. If we were to redo this experiment, it would be best to make the base solution on the same day or standardize it on the same day because water evaporates and molarity of the sodium hydroxide could change. Careful titration to the nearest half­drop would increase precision for a more accurate equivalency point. In finality, through acid­base titration, we were able to use a balanced equation to solve for moles of acetic acid, molarity of solution, and molarity of each commercial vinegar to learn that Special Value white distilled vinegar yields more acid per cost of grams.