2022 IB Diploma Extended Essays

4. Conclusion My investigation explored the question, ‘How do various titration methods compare to the Total Acidity value when titrating tartaric acid against NaOH to determine the Titratable Acidity of the wine’. My hypothesis, ‘If the TA of wine was experimentally determined … then the method using the pH data logger should result in the most accurate TA value’, was supported by the results of this investigation. As seen in Graph 1 and processed data table 2, the titration with pH data logger had the highest accuracy. The other methods’ accuracy percentages were lower by more than 10%. This is because methods 1,2 and 3 utilised the human eye to detect the colour change (endpoint) of the solution whilst method 4 constantly measured the pH during the titration. By continuously quantifying its pH, the endpoint could be accurately determined. The investigation was proved to be reliable due to the minimal uncertainties in each method, only ranging between 7 ×10−4 and 1.00×10−3 mol −3 . 5. Evaluation 5.1 Limitations and Evaluation of the Experiment Limitations How it affected the Results How it can be Improved

The acidity of the white wine slightly changed during the investigation. Despite using wine from the same brand, of the same type and from the same year, the two bottles of the wine used had different pH levels. After checking their pH levels with the pH sensor, I found that the first bottle had a pH of 3.36 whilst the second bottle had a pH of 4.7. The colour of the solution once it reached its endpoint was assumed as the colour changed at that point. As the wine originally had a yellow colour it was difficult to clearly tell when the colour drastically changed.

As a third of the trials conducted had a different initial pH, the endpoint of the wine was thus different. With different initial pH’s the volume of NaOH required to neutralise the wine would differ. Therefore, the TA would increase or decrease depending on whether the pH was 3.36 or 4.7. There is a possibility that the colour chosen was not at the wine’s endpoint but before it. This would make the volume of NaOH lower and thus the TA lower.

Several bottles of the same make can be prepared prior to the investigation and their pH can be measured. Before using another bottle during the investigation, the wine’s pH would be tested to determine if it is the same pH as the previous bottle. If it is too acidic/basic, then another bottle will be tested and used. To know the colour the wine should look like when it reached its endpoint, a pre trial should be conducted. The pH data logger should be used in a titration with the indicators. The titration will be stopped when the pH reached 8.2 and then the colour of the solution should be noted or photographed.

5.2 Discussion of future investigations As an extension of this investigation, more methods could be evaluated. For example, the potentiometric method mentioned previously could be investigated. Other colour indicators can also be investigated to determine which is the most effective. By increasing the range of the independent variable, more comparisons can be drawn and therefore the ‘most accurate’ method can be supported further.