White Phosphorus: Preparation, Properties, Structure & Uses

White Phosphorus – Preparation, Properties, Structure, Uses and Previous Year Questions

Highly Important for NEET, JEE Main/Advanced, GATE & CSIR-NET

1. Preparation of White Phosphorus

Method	Reaction / Process	Key Exam Points
From Rock Phosphate (Industrial)	Ca3(PO4)2 + 3SiO2 → 3CaSiO3 + P4O10 P3O10 + 10C → P4↑ + 10CO (Electric furnace, 1400–1600°C)	Most asked in JEE Main & GATE NEET favourite one-liner: White P is obtained by heating phosphate rock with sand and coke in electric furnace
From Bone Ash (Old Method)	Ca3(PO4)2 + 3H2SO4 → 3CaSO4 + 2H3PO4 2H3PO4 + 12C → P4 + 6H2O + 12CO	JEE Advanced & CSIR-NET level

JEE Trick: Electric furnace method → always gives white phosphorus (not red).

2. Physical Properties of White Phosphorus

Property	White Phosphorus	Comparison with Red P
Appearance	Waxy, translucent, pale yellow solid	Reddish-brown powder
Odour	Garlic-like smell	Odourless
Density	1.82 g/cm³	2.1–2.34 g/cm³
Melting Point	44.2°C	590°C (sublimes)
Solubility	Soluble in CS2, benzene, ether Insoluble in water	Insoluble in CS2 & water
Chemiluminescence	Glows in dark (greenish glow)	No glow
Ignition Temperature	Very low (~30°C)	High (~260°C)
Poisonous Nature	Highly poisonous (causes phossy jaw)	Non-poisonous
Storage	Under water (to prevent contact with air)	In air (stable)

NEET Most Repeated:
• Glows in dark → Chemiluminescence
• Garlic odour
• Stored under water
• Highly poisonous
• Soluble in CS₂

3. Structure of White Phosphorus

Tetrahedral P₄ molecule (Regular tetrahedron)

• Molecular formula: P₄
• Shape: Regular tetrahedron
• Each P atom is sp³ hybridized
• Bond angle: 60° (highly strained → very reactive)
• Contains 6 P–P single bonds
• Discrete covalent molecules (not polymeric)

JEE Advanced Favourite: “Angle strain in P₄ (60°) is responsible for its high reactivity.”

4. Chemical Properties of White Phosphorus

• Highly reactive – most reactive allotrope
• Catches fire spontaneously in air at ~30°C → P₄O₁₀
• Glows in dark due to slow oxidation (chemiluminescence)
• With halogens: Direct combination (even in dark)
• With hot conc. NaOH: Disproportionation
  P₄ + 3NaOH + 3H₂O → PH₃↑ + 3NaH₂PO₂
  (Produces phosphine + sodium hypophosphite)
• With conc. HNO₃: Oxidised to H₃PO₄
• With metals: Forms phosphides (e.g., Ca₃P₂)

CSIR-NET & JEE Advanced Classic:
P₄ + 3NaOH(hot conc.) + 3H₂O → PH₃ + 3NaH₂PO₂
Oxidation state: P(0) → P(-3) in PH₃ & P(+1) in H₂PO₂⁻

5. Uses of White Phosphorus

Use	Reason
Manufacture of rat poison	Highly poisonous
In incendiary bombs & smoke screens	Burns spontaneously, produces dense P4O10 smoke
Tracer bullets & fireworks	Chemiluminescence & spontaneous ignition
Synthesis of PCl3, PCl5, H3PO4, etc.	Starting material
Formerly used in matchsticks (strike-anywhere matches)	Banned now due to toxicity

Important for NEET:
White P was used in old strike-anywhere matches → banned due to phossy jaw disease.

Quick Comparison: White vs Red Phosphorus (Exam Favourite)

Property	White P	Red P
Structure	P4 molecules	Polymeric
Reactivity	Highly reactive	Less reactive
Ignition Temp	30°C	260°C
CS2 Solubility	Soluble	Insoluble
Glow in dark	Yes	No
Poisonous	Yes	No
Use in matches	Old strike-anywhere	Safety matches (striking surface)

High-Yield One-Liners for Last Minute Revision

• White P has P₄ tetrahedral structure with 60° bond angle → highly strained → very reactive
• Stored under water → prevents contact with oxygen
• Glows in dark → chemiluminescence due to slow oxidation
• Garlic odour + highly poisonous
• Spontaneously inflames in air at 30°C
• With hot conc. NaOH → PH₃ + NaH₂PO₂ (disproportionation)
• Used in smoke bombs and incendiary devices
• Converted to red P by heating at 573 K in inert atmosphere

Must Read White Phosphorus MCQs asked in NEET, IIT-JEE, GATE, IIT-JAM & CSIR-NET

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