The salt lead(II) iodide, sometimes known as lead iodide, has the formula PbI2. It is a bright yellow odourless crystalline solid at ambient temperature that turns orange and red when heated. It was previously known as plumbous iodide. The other name of lead is plumbum. Therefore, lead iodide is also called plumbous iodide. The name plumbous represents the +2 oxidation state of lead. Plumbous formula can be represented as Pb+2.
Why is PbI2 Formula of Lead Iodide known and PbI4 Not?
PbI2 is a known formula of lead iodide Because iodine levels in PbI4 lead to the reduction of Pb(IV) while oxidising itself from iodide to iodine. Therefore, PbI4 does not exist. This instability of PbI4 leads to the generation of PbI2. This also proves that iodide ion is a strong reducing agent for reducing Pb(IV) to Pb (II).
Preparation of Lead Iodide
In a water solution, PbI2 is usually produced by precipitating potassium iodide KI and lead(II) nitrate Pb(NO3)2:
Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3
While potassium nitrate KNO3 is soluble at normal temperature, lead iodide PbI2 is almost insoluble and consequently precipitates.
Other soluble salts containing lead(II) and iodide, such as lead(II) acetate and sodium iodide, can be used instead.
The chemical can also be made by reacting iodine vapour with molten lead at temperatures between 500 and 700 degrees Celsius.
By depositing a thin film of lead sulphide PbS and subjecting it to iodine vapour, a thin film of PbI2 can likewise be made.
PbS + I2 → PbI2 + S
Following that, the sulphur is rinsed using dimethyl sulfoxide.
Structure of Lead Iodide
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Properties of Lead Iodide
The molecular formula for Lead iodide is PbI2.
The molecular weight of PbI2 is 461.01 g/mol.
The Density (mass/volume) of Lead iodide is 6.16 g/dm3.
The Melting point of Lead iodide is 402 °C.
Boiling point of Lead iodide is 953 °C.
The colour of lead iodide is yellow. This yellow colour of lead iodide can only be seen in the precipitated form, it disappears in the solution form.
Application of Lead Iodide
Solar cells and X-ray and gamma-ray detectors are among the few specialised applications for the chemical now available. Its preparation is a fun and popular chemical demonstration that may be used to teach subjects like precipitation reactions and stoichiometry. At somewhat high temperatures, it is dissolved by light, and this effect has been employed in a proprietary photography process.
Lead iodide, often known as iodide yellow, was once used as a yellow pigment in some painters. However, due to its toxicity and lack of stability, it is no longer widely used.
Did You Know?
Lead iodide isn't used as a precursor in the production of high-efficiency solar cells.
Spin coating is used to apply a PbI2 solution in an organic solvent, such as dimethylformamide or dimethyl sulfoxide, over a titanium dioxide layer.
The layer is then annealed after being treated with a methylammonium iodide CH3NH3I solution, resulting in the double salt methylammonium lead iodide CH3NH3PbI3, which has a perovskite structure.
Lead iodide was formerly called plumbous iodide.