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Physical Properties of Potassium Iodide

Potassium iodide (KI) is supplied as odorless, colorless to white cubical or hexahedral crystals, white granules or a powder. It has a strong, bitter taste reminiscent of table salt (NaCl).

  1. Properties

    • The molecular weight of potassium iodide is 166.02 g/mol. Its melting point is 680°C (1256°F, 954 Kelvin) and its boiling point is 1330°C (2426°F). The specific gravity of potassium iodide is 3.13 at 15°C, the heat of fusion is 24.7 calories/g, and the vapor pressure is 1 mm Hg at 745°C.

    Stability

    • Potassium iodide is stable in dry air. Exposure to light and moisture can accelerate the decomposition of potassium iodide. Potassium iodide will turn yellow when exposed to air for a long time due to the liberation of iodine and the formation of small amounts of iodate. Aqueous solutions of potassium iodide can also turn yellow over time when exposed to air.

    Aqueous Solubilities

    • Aqueous solutions of potassium iodide are usually neutral of slightly alkaline. A pH of 7 to 9 is typical. So 1 g of potassium iodide is soluble in 0.7 mL of room temperature water or in 0.5 mL of boiling water. You can make a saturated solution by dissolving 30 g of of potassium iodide in 20 mL of water at 25°C.

    Other Solubilities

    • It is possible to dissolve 1 g of potassium iodide in 50 mL of absolute ethanol or in 8 mL of methanol (wood alcohol). So 1 g of potassium iodide is soluble in 75 mL of acetone, 2 mL of glycerol or 2.5 mL of glycol. Potassium iodide dissolves in elemental iodine.

    Spectra

    • The index of refraction of potassium iodide is 1.677.

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