Iodide - I<sup>-</sup>

What is Iodide?

Iodide is an anion with a valency of -1. Compounds of iodine with oxidation state as -1 are called iodides. The chemical formula for iodide is I. Iodine as an element is a halogen. It tends to accept an electron and exists as a negatively charged ion. Therefore, the anion name iodide is used interchangeable with iodine.

IUPAC name – Iodide




3.13 g/cm3, solid

Molecular Weight/ Molar Mass

126.904 g/mol

Boiling Point

184.3 °C

Melting point

113.7 °C

Chemical Formula


Iodide Structure – I

Iodide Structure

Physical Properties of Iodide – I


Irritating odour


purple-pink gas, solid iodine is dark grey or purple color.



Specific heat



128 g/100 ml (6 °C)

Chemical Properties of Iodide – I

  1. Sodium salt of iodide reacts with lead nitrate forms a yellow precipitate of lead iodide and sodium nitrate.

    Pb(NO3)2(aq) + 2 NaI(aq) → 2 NaNO3(aq) + PbI2(s)(yellow precipitate)

  2. Iodide salt of potassium reacts with chlorine forming potassium chloride and iodine. Chlorine replaces iodine because chlorine is more reactive than iodine.

    2KI + Cl2 → 2KCl + I2

Uses of Iodide – I

  • Iodide has a disinfectant property and is not readily affected as chlorine by water pH or organic content but iodide disinfectant activity is markedly reduced by cold water temperature.
  • Potassium iodide is added as a nutrient to prevent goiter a thyroid problem caused by lack of iodine and prevent a form of mental retardation associated with iodine deficiency.
  • Iodine preparations such as povidone-iodine are used to disinfect skin before surgery. Allergic reactions to iodine are common and should be carefully evaluated because the resultant stain maymask redness and swelling.

Health Hazard

The primary effects of long term oral exposure to elevated amounts of inorganic iodide are paradoxically, hyperthyroidism and hypothyroidism. Excess intake of iodide can inhibit thyroid hormone synthesis and release which may result in hypothyroidism and goitre.

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