Iodine / thiosulphate

Cards (5)

S2O3 2- is always in burette and is the standard solution.
Oxidising reagent - Potassium Iodide (KI)
Why is KI the reagent?
It reacts with Iodine ions to form iodine so solution turns yellow-brown colour
To get a more accurate end point what do we add ?
we add starch near the end point so colour change to blue-black meaning some Iodine is still present
How does the blue-black fade?
More sodium thiosulphate is added till the blue-black fades meaning all idodine has reacted