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Lead Iodide is a salt with the chemical formula PbI2. It is decomposed by light at moderately high temperatures. The preparation of lead iodide is popular in chemistry due to the formation of beautiful yellow crystals that resemble gold plates.
- Lead Iodide is derived from the Latin word plumbum.
- It is also known as Plumbous iodide or Lead (II) iodide or Lead diiodide.
- The name plumbous also represents the +2-oxidation state of lead.
- It is a bright yellow crystalline solid and odourless.
- Lead Iodide has a broad application in printing, photography, and industrial fields.
- It crystallises in thin hexagonal-shaped plates due to its hexagonal close-packed crystal structure.
- The compound is used in the manufacturing of solar cells and also as a photon detector for X-rays and gamma rays.
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Key Terms: Lead Iodide, Lead, Iodine, Solar Cells, Atoms, Van der Waals Forces, Sodium Thiosulfate, Alcohol, Sulfuric Acid, Ionic Bond, Chemical formula, Hydrogen Sulphide
What is Lead Iodide?
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Lead Iodide, also known as Lead (II) Iodide, is a yellow, odourless crystalline solid which is a heavy molecule in terms of molar mass. The compound is obtained from a double displacement reaction.
- Lead Iodide becomes orange and crimson when Lead (II) Iodide is formed.
- It was first invented in 1823 but was formally used in 1900.
- The compound is much densier as compared to other crystalline salts.
- In most cases, thin coatings of lead iodide are unstable in ambient air.
- Iodide is oxidised into elemental iodine in the presence of oxygen in the air.
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Lead Iodide Structure
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The chemical formula of Lead Iodide is Pbl2. The structure of Lead Iodide is a hexagonal close-packed system that alternates between layers of lead atoms and iodide atoms.
- The atoms are bonded to each other through ionic bonds.
- Between the lead-iodide layers, there exist weak Van der Waals forces.
- The solid form of Lead Iodide can also take a rhombohedral structure.
Lead Iodide
Properties of Lead Iodide
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The properties of lead iodide is divided into physical and chemical properties which are as follows:
Physical Properties of Lead Iodide
Following are the physical properties of Lead Iodide:
- Lead Iodide is a yellow crystalline solid.
- It is insoluble in water, alcohol and cold HCl.
- The compound is soluble in potassium iodide and concentrated sodium acetate solutions.
- It is also soluble in concentrated solutions of alkali iodides and solution of sodium thiosulfate.
- Lead Iodide is an odourless and non-combustible compound.
- The melting point and boiling point are 410 °C and 872 °C, respectively.
- The molecular weight is 461.01g/mol.
- Density of the compound is 6.6 g/cu cm which is more than that of water.
- Lead iodide decomposes when exposed to the green light at about 180°C.
The physical properties of lead iodide are tabulated as follows:
| Category | Data |
|---|---|
| Lead iodide | PbI2 |
| Molecular weight | 461.01 g/mol |
| Density | 6.16 g/dm3 |
| Boiling point | 953 °C |
| Melting point | 402 °C |
Chemical Properties of Lead Iodide
The chemical properties of lead iodide are as follows:
Reaction when exposed to Air
When a thin film of Lead Iodide when is exposed to ambient air, it forms iodine.
2 PbI2 + O2 → 2PbO + 2 I2↑
Reaction with Sulfuric Acid
Lead Iodide when reacts with concentrated sulfuric acid produces leads sulphate, hydrogen sulphide, iodine, and water.
4PbI2 + 5H2SO4 (conc.) → 4PbSO4 + 42 + H2S +4H2O
Preparation of Lead Iodide
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There are two methods for preparation of lead iodide which are as follows:
Reaction between Lead nitrate (Pb(NO3)2) and Potassium iodide (KI)
Lead nitrate (Pb (NO3)2) and Potassium iodide (KI) are both solid soluble ionic compounds that are used to prepare lead iodide. The reaction involves double-displacement of soluble Lead nitrate and Potassium iodide.
- It follows a chemical principle that when two soluble salts of the metal group react with each other.
- In this one, soluble salt is formed along with an insoluble metal salt.
- This method is known as the Bridgman-Stock Barger method.
When lead nitrate reacts with potassium iodide, the insoluble metal salt precipitates as attractive yellow crystals that can be recovered through filtration. The Lead Iodide precipitate is washed in cold water during the filtration process.
- However, if the crystals are dissolved in hot water and then recrystallized, they form golden lead iodide crystals.
- This reaction is known as the "Golden Rain" experiment.
- It produces hexagonal lead iodide crystals that look like gold plates.
- Lead iodide is more soluble in hot water; the golden rain reaction takes advantage of this.
At 80 degrees Celsius, stoichiometric proportions of lead nitrate and potassium iodide are mixed with enough water to dissolve all of the lead iodide precipitates.
- Beautiful lead iodide crystals will fall out of the solution when it cools.
- The reaction between Lead Nitrate and Potassium Iodide is
Pb (NO3)2 + 2Kl -------> Pbl2 + 2KNO3
- Net ionic equation
Pb+2 + 2l– -> Pbl2(s)
Lead Iodide
Reaction with Iodine
Another option is to react iodine vapour with molten lead between 500 and 700°C. Alternately, by depositing a thin layer of lead sulphide sand and subjecting it to iodine vapour, a thin film of Pbl2 can likewise be made.
- Dimethyl sulfoxide can be used to remove the sulphur generated during the process.
PbS + I2 → PbI2 + S
Read More:
| Class 10 Chemistry Related Concepts | ||
|---|---|---|
| Cathode Ray Discharge Tubes | Atomic Orbitals | Mole fraction |
| Quantitative Analysis | Unsaturated Hydrocarbons | Unsaturated Solution |
Uses of Lead Iodide
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The following are the uses of Lead Iodide:
- Lead Iodide is used as a precursor material in the fabrication of highly efficient solar cells.
- The compound was used as a pigment in paints under the name “ iodine yellow.”
- It is used in the art of bronzing and manufacturing gold-like mosaic tiles.
- Inorganic compound is used as an organic solvent.
- The compound is used in photography for photographic emulsions with thiols.
- It is used in films for recording optical images.
- In aerosols, lead iodide is used for cloud seeding.
- Lead Iodide is used in manufacturing mercury-vapour arc lamps.
- It is used in lubricating greases and filters for far-infrared astronomy.
- Lead Iodide is also used in making thermal batteries with iodine.
Lead Iodide Health Hazards
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Lead iodide is toxic to humans. It has a variety of acute and chronic effects that are typical of lead poisoning. Inhaling or ingesting lead iodide produces gastrointestinal problems such as colic, constipation, weakness, and even paralysis.
- This is usually noticeable in the wrist extensor muscles and less frequently in the ankles.
- The alimentary tract is irritated when a large amount of lead iodide is consumed.
- When lead iodide comes into touch with the eyes, it irritates them.
- In 1 or 2 days, pain, leg cramps, muscle weakness, paraesthesia and depression occur.
- Severe cases include unconsciousness and death.
- Lead iodide was formerly used as a paint pigment, but it is no longer used due to its toxicity and instability.
Things to Remember
- Lead iodide is made up of many small hexagonal platelets.
- It will form a yellow precipitate, giving the compound a silky look when made from cold Pb2+ and I salt solutions.
- The solubility of lead iodide in water increases considerably with temperature, allowing for larger crystals.
- High-pure iodide crystals can remove various impurities from various compounds.
- Techniques such as electron microscopy damage the samples of lead iodide.
- Lead Iodide is a very toxic substance to human health.
Sample Questions
Ques: Why is the Pbl2 formula for lead iodide known but not the Pbl4 formula? (2 marks)
Ans: Pbl2 is a well-known lead iodide formula. Because iodine levels in Pbl4 allow Pb (IV) to be reduced while oxidising from iodide to iodine. As a result, Pbl4 doesn't exist. The production of Pbl2 is caused by the instability of Pbl4. This also demonstrates that the iodide ion is an effective reducing agent for converting Pb (IV) to Pb (II).
Ques: Does Lead Iodide dissolve in water? (1 mark)
Ans: Lead iodide appears as a yellow crystalline solid. Lead Iodide does not dissolve in water, and hence Lead Iodide is insoluble in water, and it is denser than water also.
Ques: What are the uses of lead iodide? (2 marks)
Ans: Lead Iodide's physical and chemical qualities, as well as its electrical and thermal properties, makes it suitable for a wide range of applications. To begin with, it is a widely utilised semiconductor due to its non-combustible and high resistance qualities. It is utilised for X-ray and gamma spectroscopy in the medical field. It's also employed in the manufacturing of radiation detectors. It's also utilised a lot in solar cells as a fabricator.
Ques: Tell something about the reaction between Lead Nitrate and Potassium Iodide. (2 marks)
Ans: The reaction between lead nitrate and potassium iodide is an example of a precipitation reaction and double displacement reaction. Potassium iodide reacts with lead nitrate to form lead iodide and potassium nitrate.
Pb (NO3)2 + 2KI -------→ PbI2 + 2KNO3
Ques: What are the harmful effects of Lead Iodide? (2 marks)
Ans: Humans are poisoned by lead iodide. It has a wide range of acute and long-term consequences that are common in lead poisoning. Inhaling or swallowing lead iodide causes colic, constipation, weakness, and even paralysis in the gastrointestinal tract.
Ques: What are the uses of Lead Iodide? (4 marks)
Ans: The uses of lead iodide are as follows:
- Due to its wide bandgap and low noise operation, it is used as a high-energy photon detector for gamma-rays and X-rays in laboratories.
- It was used as a pigment in paints under the name “ iodine yellow”
- It is used in the art of bronzing and manufacturing gold-like mosaic tiles.
- It is used as an organic solvent.
- It is used in photography for photographic emulsions with thiols.
- It is used in films for recording optical images, in photography for photographic emulsions with thiols.
- In aerosols, Lead Iodide is used for cloud seeding.
Ques: How lead iodide can be prepared by iodine vapour? (3 marks)
Ans: Lead Iodide can also be made by reacting iodine vapour with molten lead between 500 and 700°C. By depositing a thin layer of lead sulphide sand and subjecting it to iodine vapour, a thin film of Pbl2 can likewise be made. Dimethyl sulfoxide can be used to remove the sulphur generated during the process.
PbS + I2 → PbI2 + S
Ques: What is Bridgman-Stock Barger method? (2 marks)
Ans: Lead nitrate (Pb (NO3)2) and Potassium iodide (KI) are both solid soluble ionic compounds that are used to prepare Lead iodide. The reaction involves double-displacement of soluble Lead nitrate and Potassium iodide and follows a 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. This method is known as the Bridgman-Stock Barger method.
Ques: What is Golden Rain? (3 marks)
Ans: When lead nitrate reacts with potassium iodide, the insoluble metal salt precipitates as attractive yellow crystals that can be recovered through filtration. The Lead Iodide precipitate is washed in cold water during the filtration process. However, if the crystals are dissolved in hot water and then recrystallized, they form golden Lead Iodide crystals. This reaction is known as the "Golden Rain" experiment because it produces hexagonal lead iodide crystals that look like gold plates.
Ques: What happen when lead iodide react with sulfuric acid? (2 marks)
Ans: Lead Iodide when reacts with concentrated sulfuric acid produces leads sulphate, hydrogen sulphide, iodine, and water.
4PbI2 + 5H2SO4 (conc.) → 4PbSO4 + 42 + H2S +4H2O
Ques: Mention the physical properties of lead iodide? (3 marks)
Ans: The physical properties of lead iodide are as follows:
- Lead Iodide is a yellow crystalline solid.
- It is insoluble in water, alcohol and cold HCl.
- It is soluble in potassium iodide, concentrated sodium acetate solutions concentrated solutions of alkali iodides, solution of sodium thiosulfate.
- It is odourless.
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