Question

What is the necessary condition for the preparation of metaphosphorus acid by reaction of phosphorus acid with $B{r}_2$?

• A. Simply heating
• B. Heating in a sealed tube
• C. Reaction is spontaneous
• D. None

Answer 1

The correct option is B Heating in a sealed tube

B. Heating in a sealed tube.

Pyrophosphoric acid or Orthophosphoric acid, when heated to red hot, forms metaphosphoricacid acid.

$H_4{P}_2{O}_7\to 2HP{O}_3+H_{2}O$

Crystalline phosphorus acid, on being heated with bromine in a sealed tube, gives metaphosphoricacid acid.

$H_{3}P{O}_3+B{r}_2\to HP{O}_3+2HBr$

Metaphosphoricacid acid exists as a polymer.