2022 IB Diploma Extended Essays

The pH level of the white wine was measured to be 3.36 by using a pH data logger. As 20ml of the wine will be used for all trials, the pH and volume can be substituted into equation 5 and solved as seen below. The equation is multiplied by two since tartaric acid is diprotic. = 2×10 −3 . 336 0.02 ×2 =0.0218 ×2 −3 ≈ 0.044 −3 The value calculated above, 0.044 mol −3 , will be used against the TA values determined by each titration method. Titration- Neutralisation Reaction Titration is a method that measures the volume of a reagent solution (the titrant), required to react completely with another reagent in solution. It can be used for a neutralisation reaction where an acid is titrated against a base to determine the volume of the base required to neutralise the acid completely. As the base is added to the acid, it creates a titration curve (fig.1) where the acid’s pH suddenly drops. The range at which it drops is the endpoint range, where the titration is stopped. The endpoint of a titration is the point where the acid has been fully neutralised (Royal Australian Chemistry Institute, 2019). In this investigation, various titration methods will be done to determine the volume of NaOH required to neutralise the acid of the wine fully. As white wine is a strong acid and NaOH is a strong base, its titration curve will follow the shape in figure 1. The ideal pH at white wine’s endpoint is 8.2, as outlined by Sirromet (Ferguson, n.d.). The white wine will be titrated against NaOH to create the equilibrium chemical reaction shown below. The balanced overall chemical reaction of the titration (equation 6) shows that the ratio between NaOH and tartaric Acid is 1:2. This is also because tartaric acid is diprotic, which means that it has two acidic hydrogen ions that need to be donated in two steps (equation 7) to be fully neutralised (Bylikin, et al., 2014).

Equation 6 - Overall reaction: 2 + 2 4 4 6 ⇌ 2 4 4 6 +2 + Equation 7a - step 1: + 2 4 4 6 → 4 4 6 + 2 Equation 7b - step 2: + 4 4 6 → 2 4 4 6 + 2 Titration Methods for determining TA: Titration with phenolphthalein indicator

The phenolphthalein indicator will change colour, indicating when the solution has reached its endpoint. The pH range of phenolphthalein is colourless below 8.2 and turns pink by 10 (Wyn Locke, n.d.). Therefore, the titration will need to stop as soon as the solution has a hint of pink. This ensures the solution is close to a pH of 8.2. Titration with bromothymol blue indicator The bromothymol indicator will also change colour once it has reached the endpoint, but it has a different pH range than phenolphthalein. The pH range of the bromothymol blue indicator is yellow till 6.0 and turns blue at 7.6 (Wyn Locke, n.d.).