Q.How is phosphine, $\text{PH}_3$, prepared in the laboratory? Write the equation and describe the shape of the molecule.

[!TLDR] PH3 is prepared by boiling white phosphorus with concentrated NaOH under an inert atmosphere; it is trigonal pyramidal (sp3 P, one lone pair) with an unusually small H-P-H angle. [!ANSWER] $\text{P}_4 + 3\text{NaOH} + 3\text{H}_2\t …

Phosphine is prepared in the laboratory by boiling white phosphorus with concentrated sodium hydroxide solution, carried out under an inert (oxygen-free) atmosphere because the gas evolved is spontaneously flammable if it contains traces of the impurity diphosphine, $\text{P}_2\text{H}_4$: $\text{P}_4 + 3\text{NaOH} + 3\text{H}_2\text{O} \xrightarrow{\Delta} 3\text{NaH}_2\text{PO}_2 + \text{PH}_3\uparrow$ This is a disproportionation reaction: phosphorus (oxidation state $0$ in $\text{P}_4$) is simultaneously reduced to $-3$ in $\text{PH}_3$ and oxidised to $+1$ in sodium hypophosphite. Structurally, phosphine is, like ammonia, a trigonal pyramidal molecule: phosphorus is $sp^3$ hybridised, forming three $\sigma$ bonds to the three hydrogen atoms with one lone pair, though its $\text{H-P-H}$ bond angle (about $93.6^\circ$) is notably smaller than ammonia's, since the le …

Write the disproportionation equation with its inert-atmosphere condition, then describe the pyramidal shape by an …

Forgetting the inert-atmosphere condition (relevant to why commercial phosphine ignites spontaneously); describing p …