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Booklet to help with unit 27: P7 M5 D4

Booklet to help with unit 27: P7 M5 D4. Complex ions. A Complex ion is a transition metal atom or ion + ligands A ligand is a molecule or ion which donates a pair of electrons to the transition metal ion in a complex. Nature of ligands.

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Booklet to help with unit 27: P7 M5 D4

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  1. Booklet to help with unit 27: P7 M5 D4

  2. Complex ions • A Complex ion is a transition metal atom or ion + ligands • A ligand is a molecule or ion which donates a pair of electrons to the transition metal ion in a complex

  3. Nature of ligands • Simple ligands include water, ammonia and chloride ions. • What all these have got in common is active lone pairs of electrons in the outer energy level. These are used to form co-ordinate bonds with the metal ion. • All ligands are lone pair donors. In other words, all ligands function as Lewis bases.

  4. Nature of ligands • Ligands can be neutral or negatively charged • Ligands can donate one pair of electrons (monodentate), two pairs of electrons (bidentate) or several pairs of electrons (polydentate) • H2O, NH3, Cl- and OH- are monodentate ligands

  5. Complex ions used for P7 • There main shape of complex ion that you will deal with are complexes that have six ligands This complex ion is called Hexaaqua cobalt [Co(H2O)6]2+

  6. Other complex ions This complex ion is called Hexaaqua copper This complex ion is called Hexaaqua chromium [Cu(H2O)6]2+ [Cr(H2O)6]3+

  7. Task 1: carry out practicals in hexaaqua transition metal ions

  8. Acidity of hexaaqua transition metal ions • When the lone pairs on the oxygens form co-ordinate bonds with the metal ion, there movement of electrons towards the metal ion. • That has an effect on the electrons in the O-H bonds. These electrons, in turn, get pulled towards the oxygen even more than usual. • The overall effect is that the O-H bond is weakened slightly meaning that it is easier for the water ligands to release their protons • Hence overall hexaaqua transition metal ions are acids

  9. Acidity of hexaaqua transition metal ions • Solutions containing 3+ hexaaqua ions tend to have pH's in the range from 1 to 3. Solutions containing 2+ ions have higher pH's - typically around 5 - 6, although they can go down to about 3. • In 3+ ions, the electrons in the O-H bonds will be pulled even more towards the metal ions than in 2+ ions. • That means that the hydrogen atoms in the ligand water molecules will be more readily lost - and so the 3+ ions are more acidic.

  10. Hexaaqua cobalt Reaction with sodium hydroxide Reaction with ammonia

  11. Hexaaqua cobalt Reaction with hydrochloric acid

  12. Hexaaqua cobalt Reaction with sodium carbonate

  13. Hexaaqua copper Reaction with sodium hydroxide Reaction with sodium carbonate

  14. Hexaaqua copper Reaction with Ammonia Reaction with Hydrochloric acid

  15. Hexaaqua chromium Reaction with sodium hydroxide Hydroxide ions fromsodium hydroxide solution remove hydrogen ions from the water ligands attached to the chromium ion. Once a hydrogen ion has been removed from three of the water molecules, you are left with a complex with no charge - a neutral complex. This is insoluble in water and a blue precipitate is formed.

  16. Hexaaqua chromium Reaction with ammonia This is complex is insoluble in water and is a blue precipitate

  17. Hexaaqua chromium Reaction with sodium carbonate If you add sodium carbonate solution to a solution of hexaaquachromium(III) ions, you get exactly the same precipitate as if you added sodium hydroxide solution or ammonia solution. you will get either hydrogencarbonate ions formed or carbon dioxide gas from the reaction between the hydrogen ions and carbonate ions.

  18. Hexaaqua chromium The oxidation of chromium(III) to chromium(VI) • An excess of sodium hydroxide solution is added to a solution of the hexaaquachromium(III) ions to produce a solution of green hexahydroxochromate(III) ions. This is then oxidised by warming it with hydrogen peroxide solution. You eventually get a bright yellow solution containing chromate(VI) ions.

  19. Task 2: address the question below: you carried out the following reactions: • Concentrated HCl with hexaaqua transition metal ions • Aqueous ammonia with hexaaqua transition metal ions • Aqueous sodium hydroxide with hexaaqua transition metal ions • Aqueous sodium carbonate with hexaaqua transition metal ions • For M5: Explain EACH of the chemical reactions listed above by discussing acid-base, precipitation, ligand exchange and redox reaction types. • For D5: Support your explanations by including accurate chemical equations to ALL the chemical reactions with hexaaqua transition metal ions listed above

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