2022 IB Diploma Extended Essays

Back titration The Back Titration method uses an excess amount of base to thus go past the endpoint. Another titration is performed afterwards to ‘reverse’ the reaction and determine the endpoint. This titration method uses a pH indicator which means it would still use the human eye to determine when the solution has reached its endpoint. However, the second titration enables me to get the solution closer to the endpoint after the first titration. This is because the solution will become a strong base after the first titration since there is an excess base. This solution will then be titrated against a strong acid. As seen in figure 1, a strong acid against a strong base creates an extensive endpoint range. Because this range is large, determining its endpoint is easier. Therefore, the results of the back titration should have a more accurate TA value than the titration with phenolphthalein and bromothymol indicator (Bylikin, et al., 2014). Figure 1: Titration curve

Source: (Clark, 2013) As there are essentially two titrations in a back titration, the following chemical equation is the reaction of the second titration, following equation 2. Equation 3- Back titration chemical reaction: 2 4 4 6 +2 ⇌ 2 4 4 6 +2 Titration with pH sensor The pH data logger will be connected to an external device, so the current pH of the solution will be recorded every second. The pH of the solution when it reaches its endpoint should be 8.2. Since the titration can be stopped once the solution reaches the pH of 8.2, this method should be the most accurate. Percentage Yield To find the efficiency of a reaction, the ratio of the actual value to the theoretical value is calculated using the equation below (LibreTexts, 2021). = ℎ ×100% In this experiment, the experimental value seen in the equation above will be the TA found for each method and the theoretical value will be the Total Acidity of the wine. Therefore, the equation used to determine the most accurate method is seen below. Equation 8: = ×100%