Question

In titrations involving sodium thiosulphate and potassium iodide, is it necessary to use starch solution to help us see the end point? If the colour change from yellow to colourless is easily visible, is it acceptable not to use the starch solution?

Answer 1

All of the texts I have seen say that the iodine color is dark enough that starch is not needed to see the end point; however, I also note that ALL of the texts give instructions that INCLUDE the use of starch for the end point. Personally, I KNOW my eyesight is not good enough to see the end point without starch. Having said that, if the end point IS actually visible, then it should be acceptable not to use starch (provided that one is consistent; e.g., if no aid is used to see the end point for standards, then no aid should be used for the samples).