Hydroiodic acid is prepared in laboratory by reacting iodine (I2) with hydrazine, giving hydrogen iodide and nitrogen gas.
2 I2 + NH2NH2 → 4 HI + N2
Hydroiodic acid is also prepared by bubbling hydrogen sulfide gas through an aqueous solution of iodine.
H2S + I2 → 2 HI + S
At the end of the reaction, HI is distilled to give hydroiodic acid in the desired concentrations.
1) Hydroiodic acid is a strong and reactive acid. It can react violently with ammonia, metal powders, etc., to generate fire and explosions.
2) It is highly corrosive and reacts strongly with bases. It also decomposes on heating to generate toxic fumes, and gets oxidized rapidly in air.
1) Hydroiodic acid is used to form alkyl iodides, an important class of organic compounds, by reacting HI with alkenes or primary alcohols.
2) It is also used as a reducing agent for various industrial purposes.
Hydroiodic acid is highly toxic in nature. When it comes in contact with skin and eyes, irritation occurs. It can cause severe eye damage and skin burns. Long-term exposure in low concentrations can also cause adverse health effects.