C24 reactions of inorganic compounds in aqueous solutions

• transition metal ions can become hydrated in water with H2O ligands joining around the central atom
• when transition metal ions become hydrated in water, they form a complex with an octahedral shape
• 2+ metal complexes form weaker acidic solutions than 3+ metal complexes
• the 3+ metal ions are smaller and more charged than the 2+ metal ions, so more strongly attract the electrons from the oxygen atoms in the H2O ligands, weakening more O-H bonds, causing more H+ to be released, which decreases the pH making a more acidic solution
• 3+ complexes do acid-base reactions whereas 2+ complexes do acid-base with dilute solutions and substitution with concentrated solutions
• in metal aqua ions, the water ligands can be replaced by other ligands, either if they form stronger co-ordinate bonds, or if they are present in higher concentration
• water ligands can be replaced by:

  • other neutral ligands such as NH3
  • negatively charged ligands such as Cl(-)
  • bidentate ligands such as the C2O4(2-)
  • multidentate ligands such as EDTA(4-)
• complexes formed with multidentate ligands are more stable than those formed with monodentate ligands because the multidentate ligands can form multiple bonds so fewer are required, therefore it causes the release of more entities on the right hand side of the equation than the left hand side, creating a significant entropy increase
• when $[Fe(H_2O)_6]^{2+}$is added to a little $OH^-$:

  the product is [Fe(H2O)4(OH)2]

  the colour is green gelatinous ppt
• when $[Fe(H_2O)_6]^{2+}$is added to an excess of $OH^-$:

  the product is [Fe(H2O)4(OH)2]

  the colour is green gelatinous ppt
• when $[Fe(H_2O)_6]^{2+}$is added to a little $NH_3$:

  the product is [Fe(H2O)4(OH)2]

  the colour is green gelatinous ppt
• when $[Fe(H_2O)_6]^{2+}$is added to an excess of $NH_3$:

  the product is [Fe(H2O)4(OH)2]

  the colour is green gelatinous ppt
• when $[Fe(H_2O)_6]^{2+}$is added to ${CO_3}^{2-}$:

  the product is FeCO3

  the colour is green ppt
• when $[Fe(H_2O)_6]^{2+}$is added to $Cl^-$:

  the product is [FeCl4]2-

  the colour is yellow-green ppt
• when $[Cu(H_2O)_6]^{2+}$is added to a little $OH^-$:

  the product is [Cu(H2O)4(OH)2]

  the colour is pale blue ppt
• when $[Cu(H_2O)_6]^{2+}$is added to an excess of $OH^-$:

  the product is [Cu(H2O)4(OH)2]

  the colour is pale blue ppt
• when $[Cu(H_2O)_6]^{2+}$is added to a little $NH_3$:

  the product is [Cu(H2O)4(OH)2]

  the colour is pale blue ppt
• when $[Cu(H_2O)_6]^{2+}$is added to an excess of $NH_3$:

  the product is [Cu(NH3)4(H2O)2]2+

  the colour is deep blue solution
• when $[Cu(H_2O)_6]^{2+}$is added to ${CO_3}^{2-}$:

  the product is CuCO3

  the colour is blue-green ppt
• when $[Cu(H_2O)_6]^{2+}$is added to $Cl^-$:

  the product is [CuCl4]2-

  the colour is blue-green ppt
• when $[Fe(H_2O)_6]^{3+}$is added to a little $OH^-$:

  the product is [Fe(H2O)3(OH)3]

  the colour is brown gelatinous ppt
• when $[Fe(H_2O)_6]^{3+}$is added to an excess of $OH^-$:

  the product is [Fe(H2O)3(OH)3]

  the colour is brown gelatinous ppt
• when $[Fe(H_2O)_6]^{3+}$is added to a little $NH_3$:

  the product is [Fe(H2O)3(OH)3]

  the colour is brown gelatinous ppt
• when $[Fe(H_2O)_6]^{3+}$is added to an excess of $NH_3$:

  the product is [Fe(H2O)3(OH)3]

  the colour is brown gelatinous ppt
• when $[Fe(H_2O)_6]^{3+}$is added to ${CO_3}^{2-}$:

  the products are [Fe(H2O)3(OH)3] and CO2

  the colour is brown gelatinous ppt and effervescence
• when $[Fe(H_2O)_6]^{3+}$is added to $Cl^-$:

  the product is [FeCl4]-

  the colour is cream ppt
• when $[Al(H_2O)_6]^{3+}$is added to a little $OH^-$:

  the product is [Al(H2O)3(OH)3]

  the colour is white ppt
• when $[Al(H_2O)_6]^{3+}$is added to an excess of $OH^-$:

  the product is [Al(OH)4]-

  the colour is colourless solution
• when $[Al(H_2O)_6]^{3+}$is added to a little $NH_3$:

  the product is [Al(H2O)3(OH)3]

  the colour is white ppt
• when $[Al(H_2O)_6]^{3+}$is added to an excess of $NH_3$:

  the product is [Al(H2O)3(OH)3]

  the colour is white ppt
• when $[Al(H_2O)_6]^{3+}$is added to ${CO_3}^{2-}$:

  the products are [Al(H2O)3(OH)3] and CO2

  the colour is white ppt with effervescence
• when $[Al(H_2O)_6]^{3+}$is added to $Cl^-$:

  the product is [AlCl4]-

  the colour is white ppt
• the original colour of $[Fe(H_2O)_6]^{2+}$is pale green
• the original colour of $[Cu(H_2O)_6]^{2+}$is pale blue
• the original colour of $[Fe(H_2O)_6]^{3+}$is purple/yellow/brown
• the original colour of $[Al(H_2O)_6]^{3+}$is colourless
• solutions containing 3+ ions have low pH because the ions have small size and high charge so high charge density, this weakens the OH bond in water so the water ligands release H+ ions, lowering the pH
• to convert Fe3+ ions into Fe2+ ions, use zinc in acid

  to convert Fe2+ ions into Fe3+ ions, use air