White Phosphorus

Definition

White phosphorus is a highly reactive and flammable allotrope of the chemical element phosphorus. It is a waxy, pale yellow, semi-transparent solid that emits a faint white glow when exposed to air, a phenomenon known as 'cold light'. This unique form of phosphorus is central to understanding its occurrence, preparation, and properties within the context of the chapter on phosphorus.

5 Must Know Facts For Your Next Test

1. White phosphorus is the most reactive and unstable of the four allotropes of phosphorus, the others being red, black, and violet phosphorus.
2. It is produced commercially by the thermal reduction of phosphate rock with carbon, a process that yields phosphorus vapor which is then condensed into the white phosphorus form.
3. White phosphorus is highly flammable and pyrophoric, igniting spontaneously in air at temperatures above 30°C (86°F), making it dangerous to handle and store.
4. The glow of white phosphorus in air is due to its slow reaction with oxygen, a process known as chemiluminescence, which produces the characteristic pale, greenish-white light.
5. Due to its extreme reactivity, white phosphorus has limited uses and is primarily employed in the production of phosphoric acid, phosphorus-based pesticides, and incendiary devices.

Review Questions

• Explain the occurrence and preparation of white phosphorus, including the significance of the thermal reduction process.
  • White phosphorus is not found naturally and must be produced synthetically. It is prepared commercially by the thermal reduction of phosphate rock, such as apatite, with carbon at high temperatures. This process yields phosphorus vapor, which is then condensed to form the white phosphorus allotrope. The thermal reduction is a crucial step, as it allows the extraction of elemental phosphorus from the phosphate mineral sources, making white phosphorus available for various industrial and chemical applications.
• Describe the unique physical and chemical properties of white phosphorus that make it both useful and hazardous.
  • White phosphorus is highly reactive and flammable, with a low autoignition temperature of just 30°C. This pyrophoricity, along with its ability to emit light through chemiluminescence, gives white phosphorus distinct properties. While these properties make it useful in specialized applications, such as incendiary devices, they also render white phosphorus extremely dangerous to handle and store, as it can spontaneously ignite in air, posing significant safety and environmental concerns.
• Evaluate the limited uses of white phosphorus and the potential alternatives or substitutes that could be developed to address the safety and environmental issues associated with this reactive allotrope.
  • Due to the inherent hazards of white phosphorus, its uses are relatively limited, primarily in the production of phosphoric acid, pesticides, and incendiary devices. However, the risks associated with white phosphorus have led to a growing need for the development of safer alternatives or substitutes. This could involve exploring other phosphorus allotropes, such as red or black phosphorus, which exhibit less reactivity and pyrophoricity. Additionally, research into novel phosphorus-based compounds or different manufacturing processes could yield more stable and environmentally friendly options to replace white phosphorus in various applications, while still preserving the desired chemical functionalities.

Related terms

Allotrope: An allotrope is a different structural form of the same chemical element, which can have varying physical and chemical properties.

Pyrophoricity: Pyrophoricity is the ability of a substance to spontaneously ignite in air at or below 54°C (130°F).

Phosphorescence: Phosphorescence is a type of photoluminescence where a substance emits light for a prolonged period after being excited by radiation, such as the glow of white phosphorus in air.