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Sodium iodide
CAS number 7681-82-5 Yes check.svgY
13517-06-1 (dihydrate)
PubChem 5238
RTECS number WB6475000
Molecular formula NaI
Molar mass 149.894 g/mol
Appearance white solid
Density 3.67 g/cm3
Melting point

661 °C

Boiling point

1304 °C

Solubility in water 178.8 g/100 mL (20 °C)
184 g/100 mL (25 °C)
294 g/100 mL (70 °C)
Solubility soluble in ethanol and acetone
EU Index Not listed
Main hazards Irritant, can harm the unborn child
Flash point Non-flammable
Related compounds
Other anions Sodium fluoride
Sodium chloride
Sodium bromide
Other cations Lithium iodide
Potassium iodide
Rubidium iodide
Caesium iodide
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.



Sodium iodide is commonly used to treat and prevent iodine deficiency.

Sodium iodide is used in polymerase chain reactions, and also (as an acetone solution) in the Finkelstein reaction, for conversion of an alkyl chloride into an alkyl iodide. This relies on the insolubility of sodium chloride in acetone to drive the reaction.

R-Cl + NaI → R-I + NaCl

Sodium iodide activated with thallium, NaI(Tl), when subjected to ionizing radiation, emits photons (i.e., scintillate) and are used in scintillation detectors, traditionally in nuclear medicine, geophysics, nuclear physics, and environmental measurements. NaI(Tl) is the most widely used scintillation material and has the highest light yield of the commonly used scintillators. The crystals are usually coupled with a photomultiplier tube, in a hermetically sealed assembly, as sodium iodide is hygroscopic. Fine-tuning of some parameters (i.e., radiation hardness, afterglow, transparency) can be achieved by varying the conditions of the crystal growth. Crystals with a higher level of doping are used in X-ray detectors with high spectrometric quality. Sodium iodide can be used both as single crystals and as polycrystals for this purpose.

The radioactive iodide salt of sodium, Na131I, is used for the treatment of thyroid cancer and hyperthyroidism.[1]

Solubility data

Solubility of NaI in various solvents
(g NaI / 100g of solvent at 25°C)
H2O 184
Liquid ammonia 162
Liquid sulfur dioxide 15
Methanol 62.5 - 83.0
Formic acid 61.8
Acetonitrile 24.9
Acetone 28.0
Formamide 57 - 85
Acetamide 32.3
Dimethylformamide 3.7 - 6.4


  1. ^ The Free Dictionary: sodium iodide 131I
  2. ^ Burgess, J. "Metal Ions in Solution" (Ellis Horwood, New York, 1978) ISBN 0-85312-027-7

See also

External links

Simple English

Sodium iodide

Sodium iodide is a chemical compound. It is composed of sodium and iodide ions. The chemical formula is NaI. It is a white crystalline solid. It is a weak reducing agent. When it is exposed to oxygen in the air, it turns yellow-brown. It does this because some of the iodide was oxidized to iodine. It is used to supply iodine to the human body.

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