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AP Chemistry Section 20.3 Continued

AP Chemistry Section 20.3 Continued. Devangi Laura . Phosphorous Oxides and Oxyacids. phosphorous reacts with oxygen to form oxides In these it has oxidation states of either +3 or +5

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AP Chemistry Section 20.3 Continued

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  1. AP Chemistry Section 20.3 Continued Devangi Laura

  2. Phosphorous Oxides and Oxyacids phosphorous reacts with oxygen to form oxides In these it has oxidation states of either +3 or +5 The oxide P4O6 is formed when elemental phosphorous is burned in limited oxygen and P4O6 is made when oxygen is in excess You can think of these as merely adding oxygens to the basic P4 structure Intermediate states include: P4O7, P4O8, and P4O9

  3. More Fun Stuff P4O10 Tetraphosphorousdecoxide has large affinity for water and so is powerful dehydrating agent Can be used to convert HNO3 and H2SO4 to their parent oxides (N2O5 and SO3) P4O10 dissolves in water to form phosphoric acid (H3PO4) aka orthophosphoric acid The reaction is P4O10 (s) + 6H2O (l)  4H3PO4 (aq) pure phosphoric acid is white solid melting at 42 degrees Celsius Aqueous phosphoric acid is much weaker and a poor oxidizing agent

  4. The Fun Continues Phosphate minerals are the main sources of phosphoric acid They are only found in nature in a combined state, such as Ca3(PO4)2 and Ca5(PO4)3F Fluorapatite can be converted to phosphoric acid by crushing the phosphate rock and forming a slurry with sulfuric acid Reaction: Ca5(PO4)3F (s) +5H2SO4 (aq) + 10H2O (l)  HF (aq) + 5CaSO4 + 2H20 (s) + 3H3PO4 (aq) Product gypsum is used to make wallboard for buildings, and process is called wet process, producing impure phosphoric acid

  5. Producing white phosphorous: 12Ca(PO4)3F + 43SiO2 + 90C  9P4 + 90CO + 20(3CaO . 2SiO2) + 3SiF4 White phosphorous from above is burned in air to make tetraphosphorousdecoxide, which is then combined with water to form phosphoric acid Phosphoric acid undergoes condensation reactions, meaning a water molecule is eliminated in joining of two acid molecules (picture from book)

  6. Product H4P2O7 is called pyrophosphoric acid Further heating produces polymers like tripolyphosphoric acid (H5P3O10) Sodium salt of tripolymphosophirc acid is widely used in detergents because P3O10 5- anion can form complexes with metal ions such as Mg2+ and Ca2+ which otherwise would interfere with detergent’s action

  7. Molecular structure and hybridization of central atom of phosphoric acid molecule? Hydrogen atoms are attached to oxygens Phosphorous atom is surrounded by four effective pairs, which are arranged tetrahedrally Atoms is sp3 hybridized (picture in book)

  8. When P4O6 is put in water, phosphorous acid (H3PO3) is formed. Phosphorous acid is a diprotic acid (NOT TRIPROTIC because the hydrogen atom bonded directly to the phosphorous atom is not acidic in aqueous solution. Only those bonded to oxygen atoms can be given up as protons) Third oxyacid of phosphorous is hypohosphrous acid (monoprotic)

  9. Phosphorous in Fertilizers Helps in plant growth In large quantities in soil, but often present as insoluble minerals, so hard for plants to absorb it BUT, soluble phosphate fertilizers can be made by treating phosphate rock with sulfuric acid to make superphosphate of lime, which is a mixture of CaSO4 . 2 H20 and Ca(H2PO4)2 . H2O Reaction between ammonia and phosphoric acid gives ammonium dihydrogen phosphate (super effective since in gives both nitrogen and phosphorous)

  10. Phosphorous Halides Phosphorous forms all possible halides in general forms Px3 and Px5 (only exception is PI5) The PX3 molecule has pyramidal structure Under normal conditions of temperature and pressure, PF3 is colorless gas, PCl3 is liquid, PBr3 is liquid, and PI3 is unstable red solid These PX compounds all react with water to produce phosphorous acid (reaction: PX3 + 3H2O (l)  H3PO3 (aq) + 3HX (aq)

  11. Phosphorous Halides continued In gaseous and liquid states, PX3 compounds are in trigonalbipyramidal structure But, PCl5 and PBr5 form ionic solids Solid PCl5 contains mixture of octahedral PCl6 – ions and tetrahedral PCL4 – ions and solid PBr5 has PBr4 + ions and Br- ions PX5 compounds react with water to form phosphoric acid: (reaction: PX5 + 4H2O (l)  H3PO4 (aq) + 5HX (aq)

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