Water testing method

determining residual chlorine by iodometric method using acetic acid ,potassium iodide,starch indicator and than titrate with sodium thiosulphate but the problem is some time yellow color not appear after adding potassium iodide and also in every trials blue color not appear after adding starch indicator please provide me solution by finding gaps/problem during this test.

That’s your school assignment, therefore you should work for it.Dont expect to be spoonfed by guys here.
There are many references in analytical and environmental Chemistry either in the web or the library…Focus and solve your school issues…

thanks, please provide any reference paper for my ease

You should do it yourself, it’s so easy to find it using your own keywords in your original post .

@DiegoAlonso thanks for helping , yes i checked but blue color not appear after adding starch