24.4 ligand substitution and precipitation Flashcards
what is ligand substitution?
when one ligand in a complex ion is replaced by another ligand
what happens when copper (II) sulfate is dissolved in water?
[Cu(H 2O) 6] 2+ is formed
what colour is [Cu(H 2O) 6]2+?
pale blue
what happens when excess ammonia is added to [Cu(H2O)6]2+?
what colour is [Cu(NH3)4 (H2O)2]2+ ?
dark blue
how is the ammonia added to the [Cu(H20)6]2+ ?
dropwise
what intermediate is formed when ammonia is added dropwise to [Cu(H20)6]2+ ?
Cu(OH)2
what colour precipitate is Cu(OH)2 ?
pale blue
what are the colour changes in the ligand substitution in [Cu(H2O)6]2+ ?
what are the shapes of [Cu(H2O)6]2+ and [Cu(H2O)2 (NH3)4]2+ ?
octahedral
what happens when HCl is added dropwise to [Cu (H20)6]2+ ?
what is the colour of [Cu(H20)6]2+ ?
what is the colour of [CuCl4]2- solution?
yellow
why is there a change in shape from octahedral to tetrahedral?
chloride ligands are larger than water ligands so only 4 chlorine molecules can fit in
therefore the coordination number changes from 6 to 4
what kind of reaction is ligand substitution with Cl- ions?
a reversible reaction
what would happen if the concentration of water was increased in this equation?
the EQ will shift to the left to form some [Cu(H20)6]2+ which reacts with the remaining [CuCl4]2- to form a pale green solution
this is because yellow and blue are mixed
steps of ligand substitution with chloride ions?
- [Cu(H20)6]2+ reacts with HCl to form [CuCl4]2-
- this forms a yellow solution
- when H2O is added then the EQ shifts left and a pale green solution forms
what are the colour changes in ligand substitution with chloride ions?
what is formed when chrome alum is dissolved in water?
[Cr(H2O)6] 3+
what colour is [Cr(H2O)6] 3+ ?
violet
what happens when NH3 is added dropwise to [Cr(H2O)6] 3+ ?
what colour is [Cr(NH3)6] 3+ ?
purple
what shape are both [Cr(H2O)6] 3+ and [Cr(NH3)6] 3+ ?
octahedral
what are the colour changes in the reaction if ammonia with chromium (III) ions?
what intermediate is formed when [Cr(H2O)6] 3+ reacts with excess ammonia dropwise?
Cr(OH)3 is formed
what colour is Cr(OH)3 ?
grey-green
what is a precipitation reaction?
when two aqueous solutions containing ions react together to form an insoluble ionic solid (a precipitate)
what ions do not dissolve in excess NaOH in a precipitation reacion?
Cu2+
Fe2+
Fe3+
Mn2+
what ion does NaOH provide?
OH-
Cu2+ + 2OH-
aqueous and blue
Cu(OH)2
solid and blue
Fe 2+ + 2OH-
aqueous and green
Fe(OH)2
solid and green
what happens when Fe(OH)2 reacts with air?
Fe(OH)3 forms
orange brown solid
Fe 3+ + 3OH-
aqueous and yellow
Fe(OH)3
solid and orange-brown
Mn2+ + 2OH-
aqueous and pink
Mn(OH)2
solid and light-brown
what ion does dissolve in NaOH?
Cr3+
Cr3+ + 3OH-
aqueous and violet
Cr(OH)3
solid and green
Cr(OH)3 + 3OH-
solid and green
[Cr(OH)6] 3-
aqueous and dark green
what ions are soluble in NH3?
Cr3+
Cu2+
what ions are insoluble in NH3?
Fe2+
Fe3+
Mn2+
