Question

Characteristics of potassium iodide

Answer 1

Potassium iodide behaves as a simple ionic salt, K+I−. Since the iodide ion is a mild reducing agent, I− is easily oxidised to I2 by powerful oxidising agents such as chlorine:

2 KI( aq) + Cl2(aq) → 2 KCl + I2(aq)

Even air will oxidize iodide as evidenced by the observation of a purple extract when KI is rinsed with dichloromethane. Under acidic conditions, KI is oxidised even more easily, due to the formation of hydroiodic acid (HI), which is a powerful reducing agent.

KI forms I3− when combined with elemental iodine.

KI(aq) + I2( s) → KI3(aq)

Unlike I2, I3− salts can be highly water-soluble. I2 and I3− have virtually identical redox potentials (0.535 and 0.536 V vs NHE, respectively), i.e. they are both mild oxidants relative to H2. Therefore, this reaction allows the iodine to be used in aqueous solutions for redox titrations.

Potassium iodide also serves in some organic reactions as a source of iodide ion