Phosphorus chemistry and terminology: Select the WRONG statement regarding phosphoric acid nomenclature, phosphorus allotropes, and industrial conversions.
-
A'Green acid' is the other name of phosphoric acid produced by the reaction of phosphate rock and sulphuric acid.
-
BChemically unreactive nature of red phosphorus is due to its polymeric structure.
-
CRed phosphorus is the most reactive allotropic form of phosphorus.
-
DRed phosphorus, used in safety matches, can be converted into white phosphorus by vaporisation followed by condensation.
-
EWhite phosphorus is more reactive and must be stored under water to prevent oxidation.
Answer
Correct Answer: Red phosphorus is the most reactive allotropic form of phosphorus.
Explanation
Introduction:Phosphorus occurs in multiple allotropes, primarily white (yellow) and red, which differ in structure and reactivity. Industrial phosphoric acid production routes and trade names (e.g., “green acid”) also appear in fertilizer technology. This question checks accurate recognition of these facts and flags a common misconception.
Given Data / Assumptions:
- Wet-process phosphoric acid contains impurities and is sometimes colloquially called green acid.
- Red phosphorus is polymeric and relatively stable.
- White phosphorus is molecular (P4), very reactive, and air-sensitive.
Concept / Approach:Among the allotropes, white phosphorus is substantially more reactive and toxic, readily oxidizing and even inflaming on exposure to air; therefore it is stored under water. Red phosphorus is less reactive due to its extended polymeric network, which lowers the driving force for oxidation compared with discrete P4 units. Conversion from red to white is feasible by volatilizing phosphorus and condensing to obtain the molecular allotrope.
Step-by-Step Solution:Evaluate each statement for correctness against known properties.Identify that calling red phosphorus “the most reactive” contradicts the established order (white > red).Confirm the remaining statements align with standard industrial and safety knowledge.
Verification / Alternative check:Textbook comparisons of allotropes consistently show white phosphorus as the most reactive and dangerous form; wet-process phosphoric acid is indeed impure and sometimes termed green acid.
Why Other Options Are Wrong:
- (a) True for impure wet-process phosphoric acid.
- (b) True: polymeric structure reduces reactivity.
- (d) True: conversion via vaporisation/condensation.
- (e) True: storage under water is standard practice.
Common Pitfalls:Assuming “red” implies higher reactivity; the opposite holds in phosphorus chemistry due to structural differences.
Final Answer:Red phosphorus is the most reactive allotropic form of phosphorus.