Question

PH₃ forms bubbles when passed slowly in water but NH₃ dissolves. Explain why?

On being slowly passed through water, PH₃ forms bubbles but NH₃ dissolves. Why is it so?

Answer 1

In PCl₅, phosphorus undergoes sp³d hybridisation, and a trigonal bipyramidal configuration comes into existence.

The equatorial P-Cl bonds are equivalent, while two axial bonds are different and larger than equatorial bonds.

Answer 2

1. Ammonia (NH₃) dissolves in water because it can form hydrogen bonds with water molecules due to the presence of a lone pair on nitrogen and N-H bonds.
2. Phosphine (PH₃) forms bubbles when passed through water because it cannot form hydrogen bonds with water; its bonds are weaker and mainly van der Waals forces.
3. Hence, NH₃ is highly soluble in water, while PH₃ remains largely insoluble and escapes as bubbles.

This difference arises from the ability of NH₃ to hydrogen bond, but PH₃ cannot.