Answer to Question #61691 in Inorganic Chemistry for Rhys Fyffe

Question

What element when added to KI produces a gas and changes it to yellow?

Answer 1

Air will slowly oxidize iodide ion to iodine and make the colour yellowish:
4 KI + 2 CO2 + O2 = 2 K2CO3 + 2 I2
2KI + H2O + O3 = I2↓ + O2↑ + 2KOH
KI + 2H2O + O2=4KOH + I2 ↓ + KI3
Though add traces in air may vary (carbon dioxide, water), the main oxidizing agent is a radical O'. Answer : Oxygen (O2,O3)