WebElements Periodic Table of the Elements | Potassium

Potassium compounds: potassium iodide

The potassium in potassium iodide formally is in the oxidation state 1.

Potassium iodide

Formula as often written: KI
Hill system formula: I₁K₁
CAS registry number: [7681-11-0]
Formula weight: 166.003
Class: iodide

Synonyms

potassium iodide
potassium(I) iodide

Physical properties

Colour: white
Appearance: crystalline solid
Melting point: 681°C
Boiling point: 1323°C
Density: 3120 kg m^-3

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Element analysis

Element percentages for the elements in potassium iodide
Element	%
I	76.45
K	23.55

Synthesis

One way to make potassium iodide is to react the hydroxide with hydroiodic acid. The resulting salt can then be purified by recrystallization.

KOH(aq) + HI(aq) → KI(aq) + H₂O(l)

While not a normal route of preparation because of the expense, potassium metal reacts vigorously with all the halogens to form potassium halides. So, it burns with iodine, I₂, to form potassium(I) iodide, KI.

2K(s) + I₂(s) → 2KI(s)

Solid state structure

Geometry of potassium: 6 coordinate: octahedral
Prototypical structure: NaCl (rock salt)

Crystal structure of potassium iodide

Isotope pattern

What follows is the calculated isotope pattern for the KI unit with the most intense ion set to 100%.

Formula: K₁I₁

mass  %
166 100.0 __________________________________________________
167   0.0 
168   7.2 ____

References

The data on these compounds pages are assembled and adapted from the primary literature and several other sources including the following.

R.T. Sanderson in Chemical Periodicity, Reinhold, New York, USA, 1960.
N.N. Greenwood and A. Earnshaw in Chemistry of the Elements, 2nd edition, Butterworth, UK, 1997.
F.A. Cotton, G. Wilkinson, C.A. Murillo, and M. Bochmann, in Advanced Inorganic Chemistry, John Wiley & Sons, 1999.
A.F. Trotman-Dickenson, (ed.) in Comprehensive Inorganic Chemistry, Pergamon, Oxford, UK, 1973.
R.W.G. Wyckoff, in Crystal Structures, volume 1, Interscience, John Wiley & Sons, 1963.
A.R.West in Basic solid state chemistry Chemistry, John Wiley & Sons, 1999.
A.F. Wells in Structural inorganic chemistry, 4th edition, Oxford, UK, 1975.
J.D.H. Donnay, (ed.) in Crystal data determinative tables, ACA monograph number 5, American Crystallographic Association, USA, 1963.
D.R. Lide, (ed.) in Chemical Rubber Company handbook of chemistry and physics, CRC Press, Boca Raton, Florida, USA, 77th edition, 1996.
J.W. Mellor in A comprehensive treatise on inorganic and theoretical chemistry, volumes 1-16, Longmans, London, UK, 1922-1937.
J.E. Macintyre (ed.) in Dictionary of inorganic compounds, volumes 1-3, Chapman & Hall, London, UK, 1992.