Question

How is pure phosphine prepared from phosphorous acid?

Answer 1

Hint: The molecular formula of phosphine is $P{{H}_{3}}$ and the molecular formula of phosphorous acid is ${{H}_{3}}P{{O}_{4}}$ . Means phosphorus acid should undergo reduction chemical reaction to form pure phosphine.

Complete answer:
- In the question it is asked to prepare pure phosphine from phosphorous acid.
- We should know the reaction conditions to prepare the phosphine from phosphorus acid.
- The preparation of pure phosphine from phosphorous acid is as follows.
\[\underset{phosphorous\text{ }acid}{\mathop{4{{H}_{3}}P{{O}_{3}}}}\,\xrightarrow{478-{{483}^{o}}C}\underset{phosphoric\text{ }acid}{\mathop{3{{H}_{3}}P{{O}_{4}}}}\,+\underset{phosphine}{\mathop{P{{H}_{3}}}}\,\]
- We can see that in the above chemical reaction 4 moles of phosphorus acid are going to convert into 3mole of phosphoric acid and one mole of pure phosphine at 478-483 $^{o}C$ temperature.
- Means 4 moles of phosphorus acid is mandatory to prepare one mole of pure phosphine at 478-483 $^{o}C$ temperature.
- There are several methods to prepare phosphine but from phosphorus acid we will get pure phosphine in high yield at higher temperature.

Additional information:
- Phosphine is also going to have the same structure as ammonia molecules.
- The shape of the phosphine is pyramidal.
- The hybridization of the phosphorus in phosphine is $s{{p}^{3}}$ .
- Phosphine is highly poisonous and it is soluble in water.
- Phosphine is basic in nature.

Note:
Ortho phosphorus acid is also called phosphorus acid. Phosphine is going to form ${{P}_{4}}{{O}_{10}}$ by reacting with air and it is going to act as a smoke screen and can be used in war time. From calcium phosphide also we can prepare phosphine.