3. Phosphorus

The electronic formula of phosphorus is 1s²2s²2p⁶3s²3p³3d⁰. 3s²3p³3d⁰ is the configuration of external electronic shell of phosphorus atom. In contrast to Nitrogen atom the phosphorus atom has unoccupied d-orbitals, thus gives the possibility to pass into excited state at "pair break" of 3s-electrons. According to current concept the following oxidation numbers are typical for phosphorus atom: 3-, 0, 3+, 5+:

Ground (nonexcited) state (3-, 0, 3+ oxidation number, for example, in PH₃, P, P₂O₃ compounds):

3s		3p				3d
↑↓		↑	↑	↑

The excited state (5+ oxidation number, for example, in P₂O₅ compound):

3s		3p				3d
↑		↑	↑	↑		↑	↑

The most typical phosphorus compounds are given in Table 18.

Table 18. Compounds of Phosphorus

Oxidation numbers	3-	0	1+	3+	5+
Compound	PH3	P (P2, P4, Pn)	H3PO2	P2O3, H3PO3	P2O5, H3PO4, HPO3, H4P2O7
Chemical properties	Reducing agent only	Oxidizing and reducing agents	Hypophosphorous acid, strong reducing agent	Phosphorus acid, reducing agent	Phosphoric anhydride and phosphoric acids, oxidizing agent only

Phosphorus is produced from natural Phosphates of P₂O₅ vapors reduction by coal, which is isolated from melt (at 1500⁰С) according to the reaction:

Ca₃(PO₄)₂ + 3SiO₂ 3CaSiO₃ + P₂O₅;

P₂O₅ + 5C 5CO + 2P

P5+ + 5  P0	2 (reduction);
C0 - 2  C2+	5 (oxidation).

Phosphorus behaves as the typical non-metal. It reacts with Oxygen, formed acid oxides:

4P + 3O₂ = 2P₂O₃;

4P + 5O₂ = 2P₂O₅.

Phosphorus oxides (V), phosphoric acid, Phosphates

P₂O₅ (P₄O₁₀) is very hygroscopic white powder and the most effective agent for drying. Interacting with water it forms phosphoric (monophosphoric) acid:

P₄O₁₀ + 6H₂O 4H₃PO₄.

Acid properties of P₂O₅ are shown in its interaction with hydroxides and basic oxides:

6KOH + P₂O₅ = 2K₃PO₄ + 3H₂O;

3CaO + P₂O₅ = Ca₃(PO₄)₂.

Orthophosphoric acid H₃PO₄ is threebasic acid:

H -O
H -O	P = O
H-O

At heating monophosphoric acid dehydration and formation of cyclic or linear polyphosphoric acids take place and among them diphosphoric and metaphosphoric acids are of great value:

2H₃PO₄ = H₂O + H₄P₂O₇ (diphosphoric acid);

H₄P₂O₇ = H₂O + 2HPO₃ (metaphosphoric acid).

In fact, metaphosphoric acid is inorganic polymer of cyclic structure mostly with three and four chain rings: (HPO₃)₃ and (HPO₃)₄. Diphosphoric acid and other condensed phosphoric acids with the same structure are inorganic polymers:

	O	O
	││	││
H - O -	P - O -	P -O - H
	│	│
	O-H	O-H

In Phosphate fertilizer production the extraction phosphoric acid is received by sulfuric acid action to Ca₃(PO₄)₂, which is the part of natural phosphorites and apatites:

Ca₃(PO₄)₂ + 3H₂SO₄ = 3CaSO₄ + 2H₃PO₄.

Phosphoric acid forms mono- , di- and triple-substituted salts. For example, NaH₂PO₄ - Sodium dihydroPhosphate, Na₂HPO₄ - Sodium hydroPhosphate, Na₃PO₄ - Sodium Phosphate.

The ability of phosphoric acid to react with metals, basic oxides, hydroxides and weak acid salts are used in industry for production of mineral fertilizers:

CaHPO₄ ∙ 2H₂O (precipitate);

Ca₃(PO₄)₂ + 4H₃PO₄ = 3Ca(H₂PO₄)₂;

in fact Ca(H₂PO₄)₂∙H₂O - triple superphosphate is produced.

Ca₃(PO₄)₂ + 2H₂SO₄ = Ca(H₂PO₄)₂ + 2CaSO₄ - is the receipt of simple superPhosphate. The real composition of simple superphosphate is Ca(H₂PO₄)₂∙H₂O + 2[CaSO₄∙2H₂O].

PRACTICE PROBLEMS

1. In which compounds and at which oxidation numbers can Nitrogen and phosphorus show only reducing or only oxidizing properties in the reactions and why?

2. Draw structural-graphic formulas of N₂O₃, N₂O₅, P₄O₁₀, HNO₂, HNO₃, H₃PO₄, H₃PO₃.

3. Estimate Nitrogen and Phosphorus oxidation numbers in the compounds:

NH₃∙H₂O, PH₄I, Ca(H₂PO₄)₂, NH₄H₂PO₄, Fe(NO₃)₃, Na₄P₂O₇, NH₂OH, NH₄Cl.

4. Draw the reaction equations according to transformation series:

N₂ → NH₃ → NO → NO₂ → HNO₃ → NH₄NO₃;

Ca₃(PO₄)₂ → P → P₂O₅ → H₃PO₄ → Ca(H₂PO₄)₂ → CaHPO₄;

Ca₃(PO₄)₂ → H₃PO₄ → NH₄H₂PO₄ → (NH₄)₂HPO₄.

5. Draw the diagrams of electron redistribution and put the coefficients in the equations of the following reactions:

NaNO₂ + FeCl₂ + HCl → FeCl₃ + NO + NaCl + H₂O;

NO₂ + H₂O + O₂ →

NH₄NO₃ → N₂O + H₂O →

P + HNO₃ + H₂O →

LABORATORY TRAINING

Experiment 1. Study the ammonia solution properties

A) Put 5-6 drops of Iron Chloride (III) into test-tube, add 4-5 drops of ammonia solution. Describe the color of precipitation and write the reaction.

B) Put 5-6 drops of ammonia Chloride into test-tube, add 5-7 drops of alkali solution (KOH or NaOH) and heat the mixture in water bath. Identify the isolated gas taking into account the odor and color change of pink litmus paper wetted by water, putting it into the vapor under test-tube. Draw the reaction.