Chemistry: Phosphorus

Phosphorus

Allotropes of phosphorus

1. White phosphorus

1. Name any two allotropes of phosphorus.

Chemical properties:

Action of air: When it is exposed to moist air, it produces phosphorescence, also called ghost light or cold light.

P₄ + O₂ → P₂O₅

Phosphine (PH₃)

Lab preparation of phosphine

When white phosphorous is heated with caustic soda (NaOH), phosphine gas is produced.

P₄ + NaOH + H₂O → NaH₂PO₂ + PH₃(phosphine)

sod. Hypophosphite

Or, P₄ + 6 H₂O → PH₃+ 3H₃PO₂(hypophosphorus acid)

H₃PO₂+ NaOH → NaH₂PO₂ + H₂O] *3

_{________________________________________________________________}

P₄ + 3 NaOH + 3 H₂O → PH₃(phosphine) + 3NaH₂PO₂

2. Give a balanced chemical equation for the preparation of phosphine gas.

3. What happens when white phosphorous is heated with aqueous caustic soda?

Chemical properties:

1. Basic nature: Phosphine is weakly basic (weaker than NH₃) but does not change the colour of red litmus paper. It forms phosphonium compounds

PH₃ + HCl → PH₄Cl

PH₃+ HBr → PH₄Br

PH₃+ HI → PH₄I

2. Phosphine as a reducing agent: When PH₃ gas is passed into copper sulphate solution, black ppt. of copper phosphides is formed.

CuSO₄ + PH₃ → Cu₃P₂+ H₂SO₄

Similarly, with mercuric chloride (HgCl₂), black ppt. of mercuric phosphide is obtained.

HgCl₂ + PH₃→ Hg₃P₂ + HCl

black ppt.

3. Action with Cl₂ or Br₂ gas

PH₃ + Cl₂ → PCl₃ + HCl

PH₃ + Cl₂→ PCl₅+ HCl

4. Action of air (oxygen): non-supporter of combustion. But when heated with oxygen phosphorous pentoxide or phosphoric acid is formed

PH₃ + O₂→ P₄O₁₀(P₂O₅) + H₂O

PH₃+ O₂→ H₃PO₄

Uses of phosphine gas:

*** This is not a complete note. It is just to guide you. It is recommended to study prescribed textbooks along with this material. ***

Chemistry