Question

Which of the following statements is incorrect for phosphine?
(A) It is not very soluble in water and aqueous solutions are neutral.
(B) The solution of $P{H_3}$ in water is stable even in the presence of sunlight.
(C) It does react with gaseous $HI$ to form $P{H_4}I$.
(D) The spontaneous combustion of phosphine is technically used in Holme’s signals.

Answer 1

Hint: Phosphine is a chemical compound which is categorised under organophosphorus compounds due to the presence of covalent bonds between phosphorus atom and hydrogen atom. The molecular formula of phosphine is $P{H_3}$ and the geometry of the molecule is trigonal pyramidal structure.

Complete Step by Step Solution:
In the given question, different properties of phosphine are discussed which can be explained as follows:
(i) The phosphorus atom in phosphine is less electronegative as compared to nitrogen due to which the bond between phosphorus and hydrogen is less polar that means less charge separation due to which the phosphine molecule is not very soluble in water. Due to the non-polar nature of bonds, it is more soluble in non-polar solvents.
(ii) The phosphine solution in water in the presence of sunlight decomposes to form red phosphorus along with the removal of hydrogen gas.
(iii) Phosphine molecule is feebly basic due to presence of lone pair of electrons on phosphorus atom and reacts with acids under anhydrous conditions to form corresponding salts.
Example: $P{H_3} + HX \to PH_4^ + {X^ - }$, where $X = Cl,Br,I$
(iv) Phosphine molecule has a tendency to get ignited when it comes in contact with acetylene and air resulting in the bright red coloured flames followed by fumes due to formation of calcium phosphide. Therefore, the solution is used as Holme’s signal.

As per the above properties of phosphine, we can state that the phosphine molecule in water is unstable in presence of sunlight as it undergoes decomposition reaction. Thus the statement given in option (A) is incorrect.

Therefore, the answer is option (A).

Note: It is important to note that under standard conditions, phosphine is a non-combustible gas but when it is heated in the presence of air or oxygen, it readily catches fire resulting in the formation of phosphoric acid.