Sulphur Dioxide in White Wine Lab Report

Sulphur dioxide in white wine
Date: XX/XX/XXXX
Objective
To determine the total sulphur dioxide content in a brand of white wine.
Theory
Hydrogensulphite is often added to white wine for its preservation. Only a little amount of free SO2 exist in white wine. All the available SO2 (including those from hydrogensulphite) are first converted to SO32- as illustrated by the following equations.
SO2(aq) + 2OH-(aq)  SO32-(aq) + H2O(l)
HSO3-(aq) + OH-(aq)  SO32-(aq) + H2O(l)
Addition of acid to the subsequent mixture resulting the liberation of SO2 in which its concentration by titrating with a known concentration of I2(aq) using freshly prepared starch solution as the indicator.
SO32-(aq) + 2H+(aq)  SO2(aq) + H2O(l)
SO2(aq) + I2(aq) + 2H2O(l)  2HI(aq) + H2SO4(aq)
Amount of available SO2 = amount of I2 used for titration
Reagents and apparatus
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Precautions
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Procedure
1.
The volume of wine present in the bottle stated in the label was recorded.
2.
25 cm3 of white wine was transferred into a 250 cm3 conical flask.
3.
About 12 cm3 of 1 M sodium hydroxide was added and the resulting mixture was allowed to stand for about 14 minutes.
4.
About 10 cm3 of dilute sulphuric acid and a few drops of freshly prepared starch solution were added to the flask.
5.
The mixture was titrated with 0.0050 M iodine solution.
6.
The titre required for producing the first faint and permanent blue colour was taken. 7.
Steps 2 to 6 were repeated for obtaining 2 consistent titres.
Results and Calculations
Brand name of white wine: ___________
Volume of wine as stated in label: __________
[I2(aq)] = 0.0050 M
Trial
3
Final burette reading /cm
11.00
3
Initial burette reading /cm
0.00
Volume of I2(aq) added / cm3
11.00

1st titration
20.05
10.00
10.05
mean titre /cm3

2nd titration
24.95
15.00
9.95
10.00

The calculations for determination of SO2 content in the white wine were tabulated as