Problem 3 . A red substance A (from a group V elements), when heated in the abse
ID: 907195 • Letter: P
Question
Problem 3.
A red substance A (from a group V elements), when heated in the absence of air, vaporized and re-condensed to give a yellow waxy substance B. The compound A did not react with air at room temperature, but B burned spontaneously to give clouds of a white solid C. The compound C dissolved exothermically in water to give a solution of acid D. The compound B reacted with a limited amount of chlorine to give a colorless fuming liquid E, which in turn reacted further with chlorine to give pale-yellow solid F. The compound F gave a mixture of D and hydrochloric acid when treated with water. When water was added to E, a diprotic acid G and hydrochloric acid were produced. Treatment of G with sodium peroxide resulted in a salt H of acid D. Identify substances from A to H and write balanced equations for each transformation.
Group V: Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth
Explanation / Answer
Substance A (Red phosphorus) sublimes on heating giving vapours which condense to give yellow waxy substance. .
Red phosphorus ignition temperature is much higher than that of yellow phosphorus and thus does not catch fire easily.
Phosphorus pentoxide is obtained by burning phosphorus in excess of air.
Phosphorus pentoxide react with cold water it forms meta phosphoric acid.
The compound B reacted with a limited amount of chlorine to give a colorless fuming liquid E, which in turn reacted further with chlorine to give pale-yellow solid F.
The compound F gave a mixture of D and hydrochloric acid when treated with water.
When water was added to E, a diprotic acid G and hydrochloric acid were produced.
Treatment of G with sodium peroxide resulted in a salt H of acid D.
Overall reaction is as follows:
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