Starch Iodate Paper

Starch Iodate Paper Use a mixture of equal volumes of Starch TS and potassium iodate solution (1 20). 

Make a qualitative test for H2S and SO2, at the time of performing the distillation test, see Test Method D 850. This is done by hanging a strip of filter paper moistened with the lead acetate solution and a strip of starch paper moistened with the potassium iodate solution on the end of the condenser tube. The strips are placed so that they are suspended in the upper part of the receiving cylinder so that drops of condensate pass between the strips without touching them. If, at the end of the test, the lead acetate paper shows discoloration, H2S is present but not SO2. If the lead acetate paper shows no discoloration but the starch iodate paper develops a blue color, SO2 is present but not H2S. If neither paper shows discoloration, neither H2S nor SO2 is present. 

Dip filter paper in the rest of the potassium iodate-starch mixture and suspend it in a bottle containing a little sulphurous acid. A deep blue color immediately appears in the paper. If the paper remains in the bottle the blue is very quickly bleached, leaving the paper white again. 

Sulphur Dioxide. Bum some sulphur in a deflagrating spoon in a bottle. Note the characteristic odor of the gaseous product. Lower into the bottle a piece of filter paper soaked in potassium iodate-starch solution and note the same effects as in Experiment 6. 

Sulphur bums forming sulphur dioxide SO2. The effect with the potassium iodate-starch paper constitutes a convenient test for sulphur dioxide. 

Oxidizing Action of Sulphuric Acid. In separate test tubes heat sulphur, charcoal, and copper turnings with 36 N H2S04, and hold potassium iodate-starch paper in the mouth of each tube. In each case the test paper is turned blue. 

Another method of identification of the gas is (iii) to hold a filter paper, moistened with potassium iodate and starch solution, in the vapour, when a blue colour, owing to the formation of iodine, is observable ... 

Procedure. A drop of 5 % potassium thiocyanate solution is placed on starch paper and followed by a drop of the acid test solution. A more or less intense blue stain indicates the presence of iodate. 

This test method involves a qualitative color test for H2S and SO2 that utilizes filter paper containing lead acetate and starch paper containing potassium iodate. The test is performed when carrying out the Test Method D 850 distillation test. 

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