MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Finding the end point of an iodine titration. At the start of an iodine titration the solution is brown in colour. The titrant, a standard sodium thiosulfate solution of known molarity, is titrated against the iodate solution until it becomes a pale yellow. To help to find an exact end point add a few drops of starch solution to turn it a very dark blue which sharpens the end point. Continue titrating. When the solution becomes a pale blue the end point is very close. The end point occurs when the last trace of blue disappears. The solution is now clear.
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