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Transition metals 3.2.5 and 3.2.6 > reactions in aqueous solutions 3.2.6 > Flashcards

reactions in aqueous solutions 3.2.6 Flashcards

1
Q

What is the structure of metals in a water solution?

A

the metal will have 6 water molecule ligands co-ordinately bonded by donating a lone pair from the oxygen

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2
Q

What is the colour of [Cu(H2O)6] 2+?

A

Blue

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3
Q

What is the colour of [Fe(H2O)6] 2+?

A

Green

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4
Q

What is the colour of [Fe(H2O)6] 3+? What is the real colour and why?

A

Purple
- the real colour is yellow/brown because small amounts of [Fe(H2O)5(OH)] 2+ are formed which means and H+ is lost making the solution more acidic

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5
Q

What is the colour of [Al(H2O)6] 3+ and why?

A

Colourless
- it is not a transition metal so doesn’t have an incomplete d orbital therefore no energy gap that can absorb and reflect wavelengths of light

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6
Q

What are the 3 types of reactions metal aqua ions undergo?

A

1) hydrolysis - loss of an H+ from H2O ligand
2) substitution - replacement of H2O by other ligands
3) redox - metal changes oxidation state

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7
Q

What are the reaction equations for the hydrolysis of M2+ metal aqua ions?
When does the reaction stop for Fe2+ and Cu2+ ions?

A

1) [M(H2O)6]2+ [M(H2O)5(OH)]1+ + H+
2) [M(H2O)5(OH)]1+ [M(H2O)4(OH)2] + H+
Reaction stops when a neutral complex forms

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8
Q

What are the reaction equations for the hydrolysis of M3+ metal aqua ions?
When does the reaction stop for Fe3+?
When does the reaction stop for Al3+ ions?

A

1) [M(H2O)6]3+ [M(H2O)5(OH)]2+ + H+
2) [M(H2O)5(OH)]2+ [M(H2O)4(OH)2]1+ + H+
3) [M(H2O)5(OH)]1+ [M(H2O)3(OH)3 + H+
For Fe3+ reaction stops when a neutral complex forms
For Al3+ reaction stops when an [M(OH)6]3- complex forms

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9
Q

What are the products of the hydrolysis of M2+ and M3+ ion complexes called?

A

Metal (II) hydroxides and metal (III) hydroxides

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10
Q

What does hydrolysis do to the pH of the solution of M2+ or M3+ ion complexes and why?

A

makes it more acidic due to the increase in H+

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11
Q

What is the pH of a [M(H2O)6]+ solution?

A

7

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12
Q

What is the pH of a [M(H2O)6]2+ solution?

A

6

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13
Q

What is the pH of a [M(H2O)6]3+ solution?

A

3

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14
Q

Why do M3+ ion complexes form more acidic solutions?

A
  • M3+ ions are small and highly charged so have a high charge density
  • this means they have greater polarising power which means they are more likely to break the O-H bond in water to release an H+ ion making it more acidic
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15
Q

What are the 3 bases aqua metal ions react with?

A

1) OH- ions (e.g., NaOH)
2) NH3
3) CO3 2- ions (e.g., Na2CO3)

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16
Q

What will form if a hydrolysis reaction happens with a base?

A

a neutral, insoluble complex will form as a precipitate

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17
Q

What are the observations and equation for [Fe(H2O)6]2+ when you add a small amount of OH- ions?

A

green solution to a green precipitate

[Fe(H2O)6]2+ + 2OH- = [Fe(H2O)4(OH)2] + 2H2O

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18
Q

What are the observations and equation for [Fe(H2O)6]2+ when you add excess OH- ions?

A

no visible change

19
Q

What are the observations and equation for [Cu(H2O)6]2+ when you add a small amount of OH- ions?

A

blue solution to a blue precipitate

[Cu(H2O)6]2+ + 2OH- = [Cu(H2O)4(OH)2] + 2H2O

20
Q

What are the observations and equation for [Cu(H2O)6]2+ when you add excess OH- ions?

A

no visible change

21
Q

What are the observations and equation for [Fe(H2O)6]3+ when you add a small amount of OH- ions?

A

yellow solution to a brown precipitate

[Fe(H2O)6]3+ + 3OH- = [Fe(H2O)3(OH)3] + 3H2O

22
Q

What are the observations and equation for [Fe(H2O)6]3+ when you add excess OH- ions?

A

no visible change

23
Q

What are the observations and equation for [Al(H2O)6]3+ when you add a small amount of OH- ions?

A

colourless solution to a white precipitate

[Al(H2O)6]3+ + 3OH- = [Al(H2O)3(OH)3] + 3H2O

24
Q

What are the observations and equation for [Al(H2O)6]3+ when you add excess OH- ions?

A

the white precipitate will redissolve to a colourless solution
[Al(H2O)3(OH)3] + OH- = [Al(H2O)2(OH)4]1- + H2O

25
Q

What is the summary for the hydrolysis reactions of aqua metal ions with OH- ions?

A
  • Metal (II) ions form precipitates of Metal (II) hydroxides
  • Metal (III) ions form precipitates of Metal (III) hydroxides
  • [Al(H2O)3(OH)3] is an anomaly and reacts further with OH- ions
26
Q

What are the observations and equation for [Fe(H2O)6]2+ when you add a small amount of NH3?

A

green solution to a green precipitate

[Fe(H2O)6]2+ + 2NH3 = [Fe(H2O)4(OH)2] + 2NH4+

27
Q

What are the observations and equation for [Fe(H2O)6]2+ when you add excess NH3?

A

no visible change

28
Q

What are the observations and equation for [Cu(H2O)6]2+ when you add a small amount of NH3?

A

Blue solution to a blue precipitate

[Cu(H2O)6]2+ + 2NH3 = [Cu(H2O)4(OH)2] + 2NH4+

29
Q

What are the observations and equation for [Cu(H2O)6]2+ when you add excess NH3?

A

blue precipitate dissolves to form a deep blue solution

[Cu(H2O)4)OH)2] + 4NH3 = [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH- (ligand subsitiution reaction)

30
Q

What are the observations and equation for [Fe(H2O)6]3+ when you add a small amount of NH3?

A

yellow solution to a brown precipitate

[Fe(H2O)6]3+ + 3NH3 = [Fe(H2O)3(OH)3] + 3NH4+

31
Q

What are the observations and equation for [Fe(H2O)6]3+ when you add excess NH3?

A

no visible change

32
Q

What are the observations and equation for [Al(H2O)6]3+ when you add a small amount of NH3?

A

colourless solution to a white precipitate

[Al(H2O)6]3+ + 3NH3 = [Al(H2O)3(OH)3] + 3NH4+

33
Q

What are the observations and equation for [Al(H2O)6]3+ when you add excess NH3?

A

no visible change

34
Q

What is the summary for the hydrolysis reactions of aqua metal ions with NH3?

A
  • Metal (II) ions form precipitates of Metal (II) hydroxides
  • Metal (III) ions form precipitates of Metal (III) hydroxides
  • Cu2+ is an anomaly and reacts further with NH3 by ligand substitution
35
Q

What are the observations and equation for [Fe(H2O)6]2+ when you add CO3 2- ions?

A

green solution to a green precipitate

[Fe(H2O)6]2+ + CO3 2- = FeCO3 + 6H2O

36
Q

What are the observations and equation for [Cu(H2O)6]2+ when you add CO3 2- ions?

A

Blue solution to a green/blue precipitate

[Cu(H2O)6]2+ + CO3 2- = CuCO3 + 6H2O

37
Q

What are the observations and equation for [Fe(H2O)6]3+ when you add CO3 2- ions?

A

fizzing and a brown precipitate

2[Fe(H2O)6]3+ + 3CO3 2- = 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2

38
Q

What are the observations and equation for [Al(H2O)6]3+ when you add CO3 2- ions?

A

fizzing and a white precipitate

2[Al(H2O)6]3+ + 3CO3 2- = 2[Al(H2O)3(OH)3] + 3H2O + 3CO2

39
Q

What is the summary for the hydrolysis reactions of aqua metal ions with CO3 2- ions?

A
  • Metal (II) ions form precipitates of Metal (II) carbonates
  • Metal (III) ions form precipitates of Metal (III) carbonates and bubbles of CO2 gas
  • M3+ are acidic enough to react in an acid-base reaction with basic CO3 2- ions but M2+ are not
40
Q

What metal hydroxide is amphoteric?

A

[Al(H2O)3(OH)3]

41
Q

What does amphoteric mean?

A

it can react as an acid or a base

42
Q

What are the observations and equation for when you add an alkali to [Al(H2O)3(OH)3]?

A

colourless solution to a white precipitate

[Al(H2O)3(OH)3] + OH- = [Al(H2O)2(OH)4]1- + H2O

43
Q

What are the observations and equation for when you add an acid to [Al(H2O)3(OH)3]?

A

the white precipitate will redissolve to a colourless solution
[Al(H2O)3(OH)3] + 3H+ = [Al(H2O)6]3+

44
Q

What test tube reactions test for Al3+ ions, Cu2+ ions and Fe2+/Fe3+ ions?

A

NaOH for Al3+ ions = white precipitate (precipitate dissolves with excess NaOH)
NH3 for Cu2+ ions = blue precipitate (precipitate dissolves and a deep blue solution with excess NH3)
Na2CO3 for Fe2+ ions = a green precipitate forms but no gas
Na2CO3 for Fe3+ ions = a brown precipitate forms but with CO2 gas

Transition metals 3.2.5 and 3.2.6 (2 decks)

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