Iodine potassium iodide solution

General
Surname	Iodine potassium iodide solution
other names	Lugol's solution; Potassium triiodide ( IUPAC ); Solutio Lugoli ( lat. );
Molecular formula	not applicable
Brief description	brown liquid
External identifiers / databases
EC number	235-567-5
ECHA InfoCard	100.032.321
PubChem	105053
Wikidata	Q409860
properties
Molar mass	not applicable
Physical state	liquid
density	1.12 g cm −3
safety instructions
GHS labeling of hazardous substances Caution
H and P phrases	H: 373
	P: 260-314
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Iodine potassium iodide solution (in laboratory jargon iodine iodine potassium , often used synonymously with Lugol's solution ) is a solution of iodine and potassium iodide in water. Elemental iodine is hardly soluble in pure water. However, if there are already dissolved iodide ions, the iodine dissolves with the formation of polyiodide ions:

{\ displaystyle {\ ce {2I2 + I- <=> I3- + I2 <=> I5-}}}

Therefore, iodine is dissolved together with potassium iodide.

Iodine is much more soluble in ethanol , but sometimes ethanol is undesirable as a solvent because it is flammable and evaporates quickly and can lead to undesirable side reactions. If iodine is dissolved in ethanol, the solution is called iodine tincture .

Areas of application

An iodine-potassium iodide solution is used for various purposes such as analytical chemistry and medicine . Examples are:

for Gram staining in microbiology , usually with Lugol's solution (see below)
for the detection of chitin in microscopy or in food chemistry
for the detection of starch as a so-called iodine sample , usually with Lugol's solution (see below)
for the detection of alkaloids with Bouchardat's or Wagner's reagent
as a disinfectant
as a standard solution in iodometry
Pathologists using the solution in the autopsy a amyloidosis (for. Example, in Alzheimer's disease ) demonstrated
Use for the so-called plumming with hyperthyroidism
for the fixation and preservation of phytoplankton samples
for etching gold

Lugol's solution

The Lugol solution ( Latin Solutio Lugoli ) is an iodine-potassium iodide solution (brownish red color and characteristic odor) with a mass ratio of 1: 2 of iodine to potassium iodide in water, which is also available commercially. It is named after the French doctor Jean Guillaume Lugol (1786-1851) who invented it in 1835. Lugol's solutions are usually made with an iodine content of 1%, 2% and 5%. According to the current GHS classification, all these solutions are given the GHS 08 “health hazard” classification. An iodine solution with a concentration of 0.025 mol / L (approx. 0.635% iodine) is currently not classified according to GHS, but can still be used to verify strength. According to the substitute substance test in the risk assessment in accordance with Section 5 of the Occupational Safety and Health Act , the use of the less concentrated solution is therefore recommended. As a result, the classic Lugolian solutions for demonstrating strengths become obsolete .

Mechanism of strength assessment

The proof of strength is based on a characteristic and very sensitive color reaction. The I ₅^- ions can store themselves in the starch molecules. The inclusion compound has a blue color for amylose and a brown-violet color for amylopectin . The difference is due to the fact that the amylose molecules are twisted in a helical manner, which changes the light absorption.

Individual evidence

↑ ^a ^b ^c ^d data sheet iodine-potassium iodide solution (PDF) from Carl Roth , accessed on January 26, 2016.
↑ F. Steinecke, Experimental Biology, source u. Meyer, 1983, 5th ed., P. 13.
↑ Microbiology - A work book for students, people and knowledge, 1991, 1st edition, p. 175f.
↑ Etching of gold (PDF; 368 kB). microchemicals.de, December 15, 2009.
↑ entry to Lugol solution. In: Römpp Online . Georg Thieme Verlag, accessed on May 25, 2014.
↑ LUGOL's solution in the chemical dictionary. Retrieved September 11, 2019 .
↑ Occupational Safety and Health Act §5. Retrieved September 11, 2019 .
↑ Entry on amylopectin. In: Römpp Online . Georg Thieme Verlag, accessed on March 7, 2012.

[CARLROTH-1] ta sheet iodine-potassium iodide solution (PDF) from Carl Roth , accessed on January 26, 2016.

[2] F. Steinecke, Experimental Biology, source u. Meyer, 1983, 5th ed., P. 13.

[3] Microbiology - A work book for students, people and knowledge, 1991, 1st edition, p. 175f.

[4] Etching of gold (PDF; 368 kB). microchemicals.de, December 15, 2009.

[5] try to Lugol solution. In: Römpp Online . Georg Thieme Verlag, accessed on May 25, 2014.

[6] LUGOL's solution in the chemical dictionary. Retrieved September 11, 2019 .

[7] Occupational Safety and Health Act §5. Retrieved September 11, 2019 .

[8] Entry on amylopectin. In: Römpp Online . Georg Thieme Verlag, accessed on March 7, 2012.