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Iodine and its Properties


Iodine is a black, shining (crystalline) solid. It sublimes when heated.

Physical Properties

Density (g/cm3): 4.9

Melting point (oC): 114

Boiling point (oC): 184

Solubility in water: Iodine dissolves sparingly in water. It however dissolves readily in alcohol, ether and potassium iodide solutions.

Chemical Properties

Electronegativity and reactivity: Iodine is the least in electronegativity and reactivity compared to chlorine and bromine.

Reaction with hydrogen: Iodine combines directly, but slowly with hydrogen, with heating and in the presence of a catalyst such as platinum. The reaction is reversible.

Reaction with metals and non-metals: Iodine reacts with metals and non-metals, however, the reaction is the least vigorous compared to those of chlorine and bromine.

Bleaching action: Iodine does not show any bleaching action.

Oxidizing action: Iodine is a weak oxidizing agent.

Reaction with dilute alkalis: Iodine forms iodate(I) and iodides with dilute alkalis.

Reaction with concentrated alkalis: Iodine forms iodate(V) and iodides.

Displacement reactions: Iodine does not show a displacement reaction. It does not displace chlorine or bromine from their solutions.

Compounds of Iodine

Silver Iodide: This is a yellow solid, which is insoluble in water, dilute HNO3 and ammonia solution. Light reduces it to silver.

Hydrogen Iodide: This is a colourless gas, which is soluble in water to form an acidic, constant boiling mixture. The gas is denser than air.

Oxides of Iodine: Iodine cannot show a maximum valency towards oxygen, but forms the acidic oxide I2O5 (valency of five).

compounds of iodine show the least photoelectric activity and thermal stability compared to compounds of chlorine and bromine.

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