Iodine, a diatomic molecule (I2), is an oxidizing agent and solutions of it are frequently used in chemical analyses. Iodine suffers from low solubility in water and its volatility makes it difficult to handle directly. Both these problems are overcome by the addition of an Iodide salt (usually Potassium Iodide) which forms a Triiodide (I3-) complex with the Iodine. The Triiodide complex is extremely soluble in water and has decreased volatility.

Application

Iodine solutions are typically standardized with Sodium Thiosulfate solutions or Arsenic Trioxide. The equation for reaction with Sodium Thiosulfate is:

I3- + 2 S2O32- → 3 I- + S4O62- (Dithionite ion)

See the Tech Tip under Arsenic Trioxide for information on standardization with Arsenic Trioxide.

Technical Specification

CASR No. : [7553 – 56 – 2]
EC-No. : 231-442-4
HS-No. : 2801 20 00
RTECSNN1575000
Poison class  : CH ) 2
Max. Allowable Concentration ( MAK ), Air : 1.1 mg / m3
LD 50 oral rat : 14 mg / kg
Packing category       : G
Road / Rail6.1 / 67 b
IMDG-Code61 / II UN 3290
IATA / DGR6.1 8 II UN 3290 CAO 615
PAX 613
Merck-Index10, 4881
Mol.  Formula : I2
Mol. Weight253.81
Specific Density, 20 0C4.93 g / cm3
Bulk Density~ 2100 kg / m3
Melting Range114 0C
Boiling Point185  0C
Vapour Pressure, 25 0C0.41 hPa
Solubility in H2O, 20 0C29 mg  per 100 ml
pH value ( saturated solution, H2O, 20 0C )~ 5.4
Atmospheric Susceptibilityslow sublimation