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Experiment to Determine Acidities of Wine. The purpose of this experiment is to determine the total and volatile acidities of each of the wines and compare them.

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Introduction

Experiment to Determine Acidities of Wine The purpose of this experiment is to determine the total and volatile acidities of each of the wines and compare them. Acidity is a major contributor to the taste of wines. This is especially important in white wines, because there are very little tannins found in it, so acidity can affect the taste of the wine much more than in red wines. In this experiment, 0.1M Sodium Hydroxide solution is needed for titrations. Because this is not a standard solution, it is first standardised using oxalic acid. In order to calculate the total acidity of the wine, a titration with 0.1M sodium hydroxide is carried out with a pH meter. The pH of the wine and sodium hydroxide solution is measured when a certain volume of NaOH is added each time, and a titration curve of volume against pH is plotted. The volume for the solution to reach a pH of 8.2 is recorded. This is because NaOH is a strong alkali and wine is a weak acid, so the pH lies more to the side of the alkali. A pH of 8.2 as the equivalence point is a value agreed on by winemakers. In order to calculate the total acidity of the wine, a representative acid must be used. This must be chosen because wine contains multiple different acids, which require different moles of NaOH to neutralise them. Tartaric acid was chosen as the representative acid for the wine, because it is thought to be the most abundant. ...read more.

Middle

7.8 87.5 7.9 88 8 88.5 8.1 89 8.2 89.5 8.3 90 8.4 90.5 8.5 91 8.6 91.5 8.6 92 8.7 92.5 8.8 93 8.8 93.5 8.9 94 8.9 94.5 9 95 9.1 96 9.2 97 9.3 98 9.3 99 9.4 100 9.5 101 9.6 102 9.6 103 9.7 104 9.8 105 9.8 106 9.9 107 10 108 10.1 109 10.2 110 10.3 111 10.3 112 10.4 113 10.4 114 10.5 115 10.5 Italian Volume of NaOH added (cm3 ) pH 0 3.4 3 3.5 6 3.5 9 3.6 12 3.7 15 3.7 18 3.8 21 3.9 24 4 27 4 30 4.1 33 4.2 36 4.3 39 4.4 42 4.4 45 4.5 48 4.6 51 4.7 54 4.9 57 5 60 5.1 63 5.3 66 5.5 69 5.8 72 6.1 73 6.2 74 6.3 75 6.5 76 6.6 76.5 6.6 77 6.7 77.5 6.7 78 6.8 78.5 6.8 79 6.9 79.5 7 80 7 80.5 7.1 81 7.1 81.5 7.2 82 7.3 82.5 7.3 83 7.4 83.5 7.5 84 7.5 84.5 7.6 85 7.7 85.5 7.8 86 7.8 86.5 7.9 87 8 87.5 8.1 88 8.2 88.5 8.3 89 8.4 89.5 8.4 90 8.5 90.5 8.6 91 8.7 91.5 8.7 92 8.8 92.5 8.8 93 8.9 93.5 8.9 94 9 95 9.1 96 9.2 97 9.3 98 9.3 99 9.4 100 9.5 101 9.6 102 9.6 103 9.7 104 9.8 South African Volume of NaOH added (cm3 ) pH 0 3.5 3 3.6 6 3.7 9 3.8 12 3.9 15 3.9 18 4 21 4.1 24 4.2 27 4.2 30 4.3 33 4.4 36 4.5 39 4.6 42 4.7 ...read more.

Conclusion

, the only way that was found viable, due to the small quantities of wine left after evaporation, was to mark a line at 25cm3 on the basin, and add deionised water until the solution hit that line again. This might not be very accurate, but it shouldn't matter very much, because the deionised water, along with the volatile acids, will evaporate away again, and the same number of moles of fixed acids will remain in the basin. In order to top the volume up to 25cm3 for the titration, a 25cm3 volumetric flask was used, as it was decided that this was needed to be as accurate as possible, to ensure the concentration value obtained is correct. During each titration, the pH was read less frequently at the start of the titration, and more frequently when the pH approached the equivalence point of 8.2. this was done to ensure that the volume at pH 8.2 could be read as accurately as possible, and this was achieved by adding sodium hydroxide in 0.5cm3 around pH 8.2, and in 0.1cm3 , the smallest volume a burette can read, when the pH was around 8. The standardisation of the sodium hydroxide also helped to improve accuracy, because after making the solution of NaOH up, it could just have been taken to be a 0.1M solution of NaOH. Since there are always likely to be errors in the making up of the NaOH, it was decided best to standardise it, and this was done with Oxalic Acid, a primary standard, in order to ensure that the exact concentration of the NaOH was known. ...read more.

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This is an excellent report. It uses sound theory to construct and perform a very accurate experiment. It then makes direct and legitimate conclusions. It is written well and is easy to read.

Marked by teacher Brady Smith 17/06/2012

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