Question

Why is white or yellow phosphorus always kept underwater?

Answer 1

Reactivity of allotropes of Phosphorus

• Phosphorus ($\mathrm{P}$) is a very reactive non-metal belonging to the Nitrogen family.
• White Phosphorus(${\mathrm{P}}_4$) is a waxy solid comprising tetrahedral molecules that catches fire upon contact with atmospheric Oxygen(${\mathrm{O}}_2$) due to its high reactivity.
• To cut off the oxygen supply, White Phosphorus is dipped in water, due to its insolubility in water, which prevents it from reacting vigorously.
• White Phosphorus becomes yellow in the presence of light and is equally reactive as White Phosphorus.

Reaction Mechanism

• The reaction of White Phosphorus with atmospheric Oxygen is shown below:

${\mathrm{P}}_4\left(\mathrm{s}\right)+5{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{P}}_4{\mathrm{O}}_{10}\left(\mathrm{s}\right)$

(White (Tetraphosphorus

Phosphorus) decaoxide)