Lead Iodide

What is Lead Iodide?

Plumbous Iodide or commonly known as Lead Iodide is a salt which has a widespread application as a solvent, in the medical industry and the photography industry. Essentially, Lead Iodide is derived from the reaction of potassium nitrate and Lead Iodide through the process of double displacement. Universally, the Lead Iodide formula is PbI2. It’s physical as well as chemical properties make it ideal for a wide array of applications in the printing, medical and industrial solvents realm. It is often interchangeably referred to as lead diiodide due to its structure.


What are the Physical Properties of Lead Iodide?

  • PbI2 colour is yellow crystalline solid. 

  • It is odourless. 

  • Lead Iodide has a density of 6.16 g/cm3. 

  • Lead Iodide is denser than water and is insoluble in most liquids, barring boiling water and potassium iodine.  

  • The melting point of Lead iodide is 402 °C.

  • The boiling point is 953 °C.

  • The molecular weight of Lead Iodide is 461.01 g/mol

  • The thermal conductivity is 26.864.3 10-3 W cm-1 K

  • Lead Iodide is non-combustible

Lead Iodide Structure

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When looked through X-ray powder diffraction, Lead Iodide resembles a hexagonal close-packed system. It alternates between layers of iodine and lead atoms. It is mostly ionic bonds with weak Van der Waals interactions. Lead iodide solid can also take a rhombohedral structure.

What are the Chemical Properties of Lead Iodide?

Lead Iodide belongs to the Lead-14 and the Iodine-17 group and is a part of the P-3mI symmetrical group. As mentioned earlier the chemical formula of Lead Iodide is PbI2. Lead Iodide is highly resistant to a large spectrum of temperature and portrays extreme chemical stability. This makes it an ideal ingredient for film development and also as an oxidizing agent. 

In ambient air (oxygen), thin films of Lead Iodide, however, is quite unstable and forms iodine.

2 PbI2 + O2 → 2 PbO + 2 I2↑ 

It has a molar mass of 461.01 g/mol. 

Lead(II) iodide reacts with concentrated sulfuric acid to produce lead(II) sulfate, hydrogen sulfide, iodine and water.

4PbI2 + 5H2SO4 (conc.) →  4PbSO4 + 4I2 + H2S +4H2O

Now that we know the properties of Lead Iodide, let us now understand the process of the formation of Lead Iodide. 

How is Lead Iodide prepared?

The chemical formula Lead Iodide involves the double displacement of soluble lead nitrate and potassium iodine. The product of this chemical reaction is a yellow, colourless solid Lead Iodide and the by-product is a potassium nitrate solution. This follows the chemical principle that when two soluble salts of the metal group react with each other, one soluble salt is formed along with an insoluble metal salt. In our case, the later is PbI2 or Lead Iodide. This method is known as the Bridgman-Stockbarger method. 

Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3

This insoluble metal salt precipitates as yellow crystals and is recovered through the process of filtration. This is referred to as the “golden rain”. Typically, this filtration process involves washing the Lead Iodide precipitate in cold water. However, if they are dissolved in hot water and then allowed to recrystallise, they form fascinating golden crystals of Lead Iodide. Care must be taken that any amount of soluble Lead Iodide is removed, to get unadulterated PbI2. This may be done by allowing it to react with a hot composition of any bicarbonate. This will result in a cloudy lead carbonate precipitate which then can be easily segregated from Lead Iodide using filtration and we will be left with the golden crystals of Lead Iodide.

Alternatively, one may also produce Lead Iodide by getting iodine vapour to react with molten lead, at a controlled temperature ranging between 500 degrees to 700 degrees celsius.

No matter how spectacular the formation of Lead Iodide may be, it entails several health hazards. This is because any lead-bearing compounds can be highly toxic, especially when heated. Hence, adequate precautions must be taken while chemically preparing Lead Iodide.

FAQ (Frequently Asked Questions)

1. What is Lead Iodide Used for?

The physical, as well as chemical properties of Lead Iodide along with its electrical and thermal features, makes it conducive for a wide array of applications. To begin with, its non-combustible, high resistant properties have made it a commonly used semiconductor. In the domain of medicine, it is used for X-ray and gamma spectroscopy. It is also used for the fabrication of radiation detectors. It is also used frequently as a fabricator in solar cells. 

Lead Iodide is usually in demand in the solvent industry as an organic solvent and is often used as an oxidizing agent. Due to this property, Lead Iodide is a basic material in the field of bronzing, in developing films and photography development. 

In many ways, Lead Iodide as a chemical compound has been underutilised due to the material setbacks of the industrial devices. But its high photoelectric efficiency expands its scope of potential use in the future.

2. What are the Safety Measures to be Followed in the Course of the Formation of Lead Iodide?

Some of the safety measures that must be mandatorily observed while preparing Lead Iodide entails avoiding direct exposure to the PbI2 crystals. Hence protective equipment and maintaining a safe distance from the compound at all points is imperative. 

In the event of one accidentally inhaling or swallowing any bit of the compound, the medical intervention must be sought immediately. Exposure to Lead Iodide can trigger off several health impairments including infertility, gastrointestinal ailments, constipation and in some extreme situations can also cause paralysis. To avoid any cumulative health hazard, one must seek medical attention, if one happens to ingest Lead Iodide in the course of its preparation. However, there isn’t any need for alarm since usually, such conditions are reversible with proper and timely treatment.