Practical investigations
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Hi, I'm investigating the SO2 content in wines. I have completed my experiment into finding the Total, Free and Bound SO2 in the wines and have the titration results from the ripper method. However, I am unsure what the amount of SO2 is measured in, and how to calculate it. Here are my results for my white wine:
Concentration of iodine = 0.000423 M
Volume of iodine used = 12.8 ml
Wine sample volume = 10.0 ml
I tried using the equation MV/n = MV/n.
Is this correct and what are the units? How do I get my results from the equation to fit the units?
Igloo writes ....
I would not recommend the use of a formula when carrying out titration calculations. First you need to know that when a solution of iodine oxidises sulphur dioxide the reaction below occurs:
I2(aq) + SO2(aq) + 2H2O(l) ----> 2HI(aq) + H2SO4(aq)
This tells us that one mole of sulphur dioxide reacts with exactly one mole of iodine. Before beginning the calculation decide which of the reagents is the reference chemical, i.e. for which chemical are both the concentration and volume used known? In your case this is the iodine.
The calculation itself is carried out in three distinct stages:
[1] Calculate the number of moles of the reference reagent - you know the concentration of the iodine solution in mol dm-3 and the volume used (from the burette) in cm3 (ml). You should thus be able to work out the number of moles of iodine used in the titration.
[2] Use the equation to deduce the moles used of the other reagent, SO2, present in the titration. Since one mole of iodine reacts with one mole of sulphur dioxide, it should be obvious!
[3] Work the concentration of the SO2 in mol dm-3.. The amount of sulphur dioxide in [2] is present in 10 cm3 (10 ml), so it is easy enough to deduce what must be present in 1000 cm3 (1 dm3)
You now have the concentration of sulphur dioxide. If you multiply this value by the molar mass of sulphur dioxide, you can convert the concentration to g dm-3, and since this value is likely to be quite low, multiplying by another 1000 converts it to mg dm-3, which is the way in which the concentration of sulphur dioxide in wines is normally expressed.
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updated: 17 April 2007
