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Difficulty: HardOxidation Numbers and IUPAC Nomenclature of Redox Species
During the disproportionation reaction of white phosphorus (P4P_4) in an alkaline aqueous medium, phosphorus reacts according to the equation:
P4+3OH−+3H2O→PH3+3H2PO2−P_4 + 3OH^- + 3H_2O \rightarrow PH_3 + 3H_2PO_2^-
What are the oxidation numbers of phosphorus in P4P_4, PH3PH_3, and H2PO2−H_2PO_2^- respectively, and what is the systematic IUPAC name of the H2PO2−H_2PO_2^- ion?
  1. 00, −3-3, and +1+1; Dihydrogendioxophosphate(I) ionAnswer
  2. B
    +4+4, −3-3, and +1+1; Dihydrogendioxophosphate(III) ion
  3. C
    00, +3+3, and +3+3; Dihydrogentrioxophosphate(III) ion
  4. D
    −4-4, +3+3, and +5+5; Dioxophosphate(V) ion

Answer

The oxidation numbers of phosphorus in P4P_4, PH3PH_3, and H2PO2−H_2PO_2^- are 00, −3-3, and +1+1 respectively, and the systematic IUPAC name of H2PO2−H_2PO_2^- is the Dihydrogendioxophosphate(I) ion.
The option stating '00, −3-3, and +1+1; Dihydrogendioxophosphate(I) ion' is correct because uncombined phosphorus (P4P_4) has an oxidation number of 00. In phosphine (PH3PH_3), phosphorus has an oxidation state of −3-3 because hydrogen is +1+1. In H2PO2−H_2PO_2^-, solving 2(+1)+x+2(−2)=−12(+1) + x + 2(-2) = -1 gives x=+1x = +1. Following IUPAC rules for oxoanions with hydrogen ligands, two hydrogens ('Dihydrogen'), two oxygens ('dioxo'), and phosphorus(I) in an anion ('phosphate(I)') combine to form the name Dihydrogendioxophosphate(I) ion.

Step-by-Step Solution

1
Determine the oxidation state of phosphorus in P4P_4.
Oxidation state = 00
By definition, any element in its free, uncombined elemental state has an oxidation number of zero.
2
Determine the oxidation state of phosphorus in PH3PH_3.
Oxidation state = −3-3
Hydrogen bonded to non-metals has an oxidation state of +1+1. Setting up the equation: x+3(+1)=0  ⟹  x=−3x + 3(+1) = 0 \implies x = -3.
3
Determine the oxidation state of phosphorus in H2PO2−H_2PO_2^-.
Oxidation state = +1+1
Hydrogen is +1+1 and oxygen is −2-2. Setting up the ion charge equation: 2(+1)+x+2(−2)=−1  ⟹  +2+x−4=−1  ⟹  x=+12(+1) + x + 2(-2) = -1 \implies +2 + x - 4 = -1 \implies x = +1.
4
Derive the systematic IUPAC name for H2PO2−H_2PO_2^-.
Dihydrogendioxophosphate(I) ion
The polyatomic ion contains 2 hydrogen atoms ('Dihydrogen'), 2 oxygen ligands ('dioxo'), the central phosphorus atom in an anion suffix ('phosphate'), and Roman numeral '(I)' indicating its +1+1 oxidation state.

Key Concept

Calculation of oxidation states in polyatomic ions and application of inorganic IUPAC nomenclature rules.
Estimated Time:2m 0s
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Topics

Oxidation Numbers and IUPAC Nomenclature of Redox Species

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