Question

Write main differences between the properties of white phosphorus and red phosphorus.

Answer 1

Hint: There exist many allotropic forms of phosphorus in nature. Red phosphorus and white phosphorus are two the most common and important allotropes of phosphorus. Red phosphorus is thermally more stable than white phosphorus.

Complete answer:
Main points of difference between the properties red phosphorous and white phosphorous are tabulated below:

Property	White phosphorous	Red phosphorous
Physical state and colour	It is a white waxy solid. It is soft and can be cut using a knife. It turns yellow in colour in exposure to light, hence, it is also called as yellow phosphorus.	It is red coloured hard crystalline solid. It is lustrous in nature.
Odour	It has garlic like odour.	It is odourless.
Physiological properties	It is poisonous in nature and prolonged working this phosphorus leads to a disease known as Phossy jaw.	It is non-poisonous in nature.
Structure	White phosphorus exists in ${{P}_{4}}$ tetrahedral structure. Each P-atom is $s{{p}^{3}}$ hybridized and bonded to other three P-atoms by covalent bonds.	Red phosphorus exists in polymeric form. Each ${{P}_{4}}$ tetrahedral is linked to another to form a polymer through covalent bonds. Its melting point is higher than that of white phosphorus,
Solubility	It is insoluble in water but dissolves in organic solvents for example, ether, carbon disulphide, alcohols, etc	It is not soluble in water as well as organic solvents
Action of air	It shows phosphorescence. Due to high angle strain, it is very reactive. It burns in air. The greenish glow is visible in the dark	It does not glow in the dark. Due to its polymeric, it is less reactive than white phosphorus. On reaction with oxygen it gives ${{P}_{4}}{{O}_{10}}$.
Reaction with halogens	It spontaneously burns in chlorine to form phosphorus trichloride and phosphorus pentachloride. \[{{P}_{4}}+6C{{l}_{2}}\to 4PC{{l}_{3}}\] \[{{P}_{4}}+10C{{l}_{2}}\to 4PC{{l}_{5}}\]	Being less reactive, it reacts with halogens only when heated. It forms $PC{{l}_{3}}$ followed by $PC{{l}_{5}}$. \[{{P}_{4}}+6C{{l}_{2}}\xrightarrow{\Delta }4PC{{l}_{3}}\] \[{{P}_{4}}+10C{{l}_{2}}\xrightarrow{\Delta }4PC{{l}_{5}}\]
Reaction with sulphur	It reacts with sulphur with violently to form a number of sulphides, i.e. ${{P}_{2}}{{S}_{3}}$, ${{P}_{2}}{{O}_{5}}$, ${{P}_{4}}{{S}_{3}}$, ${{P}_{4}}{{S}_{7}}$and ${{P}_{4}}{{S}_{10}}$. ${{P}_{4}}{{S}_{3}}$ being the most stable. \[8{{P}_{4}}+3{{S}_{8}}\to 8{{P}_{4}}{{S}_{3}}\]	It reacts with sulphur only when heated in an inert atmosphere to form sulphides. \[8{{P}_{4}}+3{{S}_{8}}\xrightarrow{453K}8{{P}_{4}}{{S}_{3}}\]
Reaction with metals	It reacts with metals to convert them into phosphides.	It generally does not react with metals. It may show reactions with alkali metal like Na at high temperature.
Reaction with base	White phosphorous when heated with solution of sodium hydroxide (NaOH) solution in inert atmosphere forms phosphine ($P{{H}_{3}}$) and sodium hypophosphite ($Na{{H}_{2}}P{{O}_{2}}$). \[{{P}_{4}}+3NaOH+3{{H}_{2}}O\xrightarrow{\Delta ,C{{O}_{2}}}P{{H}_{3}}+3Na{{H}_{2}}P{{O}_{2}}\]	It does show reaction with sodium hydroxide. This property is exploited to separate red phosphorus from white phosphorus.

Note: The main point to note here is that red phosphorus exists in polymeric form and thus, is less reactive than white phosphorus. White phosphorus being less stable than red phosphorus, can be converted to red phosphorus by heating at 573K for several hours.