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Analytical Procedures - SO2 in Acid
February 12, 2002
The analysis of sulphur dioxide (SO2) in sulphuric acid is generally done to determine the level of SO2 in the product acid. The presence of high concentrations of SO2 into the acid means that the product acid stripper or crossflow stripper isn’t working properly.
The analysis of SO2 is performed by oxidizing it with an excess of iodine and titrating the excess with sodium thiosulphate.
Place ~400 ml of water in a 600 ml Erlenmeyer flask. Add 10 ml of 0.1 N iodine solution, and, gently, 50 cc of sulphuric acid (weighed). Shake well with a glass rod and titre the excess of iodine with 0.1 N thiosulphate solution. When the yellow colour of the solution is beginning to disappear, add a few millilitres of starch solution and continue titring to colourless.
ppm = ( V1 x f1
- V2 x f2 ) x 3.2 x 103 /
SO2 ppm = ( V1 x f1 - V2 x f2 ) x 3.2 x 103 / W
= ml of 0.1 mol/L iodine solution used
V2 = ml of 0.1 mol/L thiosulphate solution used
W = grams of sample weighed
f1 = corrective coefficient of 0.1 mol/L iodine solution
f2 = corrective coefficient of 0.1 mol/L thiosulphate solution