Ligand substitution and precipitation
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38 Terms
What is a ligand substitution reaction?
a reaction where one ligand in a complex ion is replaced by another
When copper (II) sulphate is dissolved in water what is formed?
[Cu(H2O)6]2+
What colour is [Cu(H2O)6]2+ ?
pale blue
What is formed when excess aqueous ammonia is added to [Cu(H2O)6]2+?
[Cu(NH3)4(H2O)2]2+
What colour is [Cu(NH3)4(H2O)2]2+ ?
dark blue
What is formed when ammonia is added DROP-WISE to [Cu(H2O)6]2+?
Cu(OH)2 SOLID
What colour is Cu(OH)2 ?
pale blue precipitate
What is formed when excess HCl is added to Cu2+(aq)?
[CuCl4]2-
What colour is [CuCl4]2-
yellow
How is the reaction between [Cu(H2O)6]2+ and excess HCl a ligand substitution? Why odes a coordination number change?
six water ligands have been substituted for 4 chloride ligands
chloride ligands are larger in size than water ligands - fewer chloride ligands can fit around the central ion
What colour is [Cr(H2O)6]3+
pale purple
due to impurities of Cr3+ it often appears green
How do you form [Cr(H2O)6]3+?
when KCr(SO4)2.12(H2O) is dissolved in water
What is formed when [Cr(H2O)6]3+ reacts with an excess of aqueous ammonia?
forms [Cr(NH3)6]3+
What colour is [Cr(NH3)6]3+?
purple
The 4 protein chains present in haemoglobin are held together by what?
weak intermolecular forces
Each protein chain has a what?
haem group
What is present at the centre of a haem molecule?
iron (II)
Are oxygen good ligands or not? What does this mean?
They’re not very good ligands so they bond weakly to the iron(II)
weak bond allows them to break off easily and be transported to the cells
Is CO a good ligand or not? What does this mean?
better ligand than oxygen - binds strongly and irreversibly to the iron(II)
prevents oxygen being carried to the cells
What is it called when oxygen binds to the haemoglobin?
oxyhemoglobin
How does ligand substitution occur when carbon monoxide binds?
oxgyen is substituted for carbon monoxide
What is the complex called when carbon monoxide binds to haemoglobin?
carboxyhaemoglobin
What happens if the concentration of carboxyhaemoglobin becomes too high?
oxygen transport is prevented - death
What is formed when Fe2+ reacts with sodium hydroxide?
Fe(OH)2 SOLID
What colour is Fe(OH)2?
dark green precipitate
What can Fe2+ also be written as? What colour is this?
[Fe(H2O)6]2+
pale green
What happens to Fe(OH)2 at the surface?
turns brown as iron(II) is oxidised to iron(III)
orange-brown precipitate is Fe(OH)3
What colour is Fe3+ / [Fe(H2O)6]3+ ?
yellow
What happens when NaOH is added to Fe3+?
orange-brown precipitate
Fe(OH)3 is formed
What colour is Mn2+ / [Mn(H2O)6]2+?
pale pink solution
What happens when NaOH is added to Mn2+?
pale brown precipitate forms
Mn(OH)2
Which precipitates are SOLUBLE in excess sodium hydroxide?
Cr(OH)3
What is formed when NaOH is added to Cr3+?
forms green precipitate of Cr(OH)3
What is formed when excess sodium hydroxide is added to Cr(OH)3?
forms a dark green solution of [Cr(OH)6]3-
What are the only compounds that react with excess NH3?
Cr(OH)3 and Cu(OH)2
What is formed when water and excess HCl is added to CoCl26H2O?
blue solution
What does ammonia act as when added to [Cu(H2O)6]2+?
ammonia acts as a base
What are the equations for the reaction between ammonia and [Cu(H2O)6]2+?
NH3 + H2O ⇌ NH4+ + OH-
Cu2+ + 2OH- → Cu(OH)2
(for when ammonia is NOT in excess)
Note 
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