Chapter 24: Transition Elements Reactions Flashcards

1
Q

What are ligand substitution reactions?

A
  • Reactions where one ligand in a complex ion is replaced with another
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2
Q

What happens when copper sulfate is dissolved in water?

A
  • The complex ion [Cu(H2O)6]2+ is formed
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3
Q

What does [Cu(H2O)6]2+ look like?

A
  • Pale blue solution
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4
Q

What happens when ammonia is added to [Cu(H2O)6]2+ ? What are these types of reactions called?

A
  • First as ammonia is added dropwise, a blue precipitate, Cu(OH)2 is formed
  • Precipitation
  • After an excess of ammonia is added, [Cu(NH3)4(H2O)2]2+, a dark blue solution, is formed
  • Ligand substitution
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5
Q

What happens when concentrated HCl is added to [Cu(H2O)6]2+ ?

A
  • [Cu(Cl)4]2- is formed, a yellow solution
  • Before the reaction is complete, the solution is green due to both the blue and yellow solutions being present
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6
Q

Give the equation for the formation of [Cu(Cl)4]2- from [Cu(H2O)6]2+ . Add an extra detail. Why does [Cu(Cl)4]2- have 4 ligands? What shape is it?

A
  • [Cu(H2O)6]2+ + 4Cl- <-> [Cu(Cl)4]2- + 6H2O
  • Since the reaction is reversible, adding water would create a blue solution again
  • Chloride ligands are bigger than other ligands, such as water and ammonia, so copper’s coordination number changes
  • Tetrahedral
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7
Q

What happens when [Cr(H2O)6]3+ is reacted with excess ammonia?

A
  • [Cr(H2O)6]3+ is a violet solution
  • As ammonia is added dropwise, a grey-green precipitate, Cr(OH)3 is formed
  • After an excess of ammonia is added, [Cr(NH3)6]3+, a purple solution, is formed
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8
Q

How does carbon monoxide poisoning work?

A
  • Oxygen binds to the Fe2+ ion in haemoglobin
  • It is then released where it is needed in the body
  • The problem with is that carbon monoxide’s bond with the Fe2+ ion is stronger than oxygen’s
  • Carbon monoxide therefore replaces oxygen
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9
Q

What colour are iron (II) ions in solution, and after: adding aqueous sodium hydroxide and ammonia, and excess sodium hydroxide and ammonia?

A
  • Pale green solution
  • After adding aqueous sodium hydroxide/ ammonia: green precipitate, but turns brown if left in air as iron (II) is oxidised to iron (III)
  • In excess sodium hydroxide/ ammonia: no change; the precipitate is insoluble
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10
Q

What colour are iron (III) ions in solution, and after: adding aqueous sodium hydroxide and ammonia, and excess sodium hydroxide and ammonia?

A
  • Pale yellow solution
  • After adding aqueous sodium hydroxide/ ammonia: orange-brown precipitate
  • In excess sodium hydroxide/ ammonia: no change, the precipitate is insoluble
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11
Q

What colour are manganese (II) ions in solution, and after: adding aqueous sodium hydroxide and ammonia, and excess sodium hydroxide and ammonia?

A
  • Pale pink solution
  • After adding aqueous sodium hydroxide/ ammonia: light brown precipitate, but turns dark brown if left in air
  • In excess sodium hydroxide/ ammonia: no change, the precipitate is insoluble
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12
Q

What happens to [Cu(H2O)6]2+ when aqueous sodium hydroxide is added?

A
  • At first, Cu(OH)2 is formed
  • However, since the precipitate is insoluble in excess NaOH, it remains a blue precipitate
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13
Q

What happens to [Cr(H2O)6]3+ when aqueous sodium hydroxide is added?

A
  • At first, Cr(OH)3 is formed
  • Then [Cr(OH)6]3- is formed, which is a dark green solution
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14
Q

What can oxidise iron (II) to form iron (III)? What is the colour change when this happens, and what causes it?

A
  • Manganate ions in acidic conditions (MnO4-, H+)
  • Purple to colourless
  • Manganate ions are purple, but manganese (II) ions are colourless
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15
Q

What can reduce iron (III) to form iron (II)? What is the colour change when this happens, and what causes it?

A
  • Iodide ions
  • Orange-brown to brown
  • Iron (III) ions are orange-brown, and iron (II) ions are pale green, but their colour is not visible as iodine is formed, which is brown
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16
Q

What can be used to reduce dichromate ions? Construct the equation. What is the colour change?

A
  • Zinc
  • Dichromate ions can be reduced to chromium (III) ions
  • Zinc is oxidised to form zinc (II) ions
  • Orange to green
17
Q

Give an example of a reaction where chromium (III) is oxidised to chromium (VI). What is the colour change?

A
  • Chromium (III) ions are oxidised by alkaline hydrogen peroxide to form chromium (VI) in CrO4^2-, making the solution yellow (chromium turns green when reacted with NaOH)
  • (Because the reaction takes place in alkaline conditions, balance each half equation using the alkaline method)
18
Q

What can copper (II) ions be reduced by? What happens in this reaction? What observations can be made?

A
  • Iodide ions
  • Copper (I) iodide and iodine are formed
  • CuI is a white precipitate, and iodine is brown
  • So, there is an overall change from pale blue to brown, with the precipitate of CuI visible at the bottom
19
Q

When does copper disproportionate? Give the equation. What colour changes are there?

A
  • When copper (I) oxide is reacted with hot dilute sulfuric acid
  • Cu2O + H2SO4 -> Cu + CuSO4 + H2O
  • A brown precipitate of copper and a blue solution of copper sulfate is formed