Question
What happens when iodine is added to potassium iodide solution?
Solution
Iodine is not very soluble in water, therefore the iodine reagent is made by dissolving iodine in water in the presence of potassium iodide. This makes a linear triiodide ion complex with is soluble. The triiodide ion ion slips into the coil of the starch causing an intense blue-black colour.
KI → K+ + I-
I2 + I- → I3-
Thus the reaction of
I2 + 2KI → KI + KI3
