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AQA A Level Inorganic Chemistry > 6. Reactions of ions in aqueous solution > Flashcards

6. Reactions of ions in aqueous solution Flashcards

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1
Q

When does complex formation occur?

A

When a positively charged transition metal ion attracts a ligand with a lone pair of electrons, which forms a coordinate bond with the central ion

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2
Q

What is a Lewis base?

A

An electron pair donor

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3
Q

What is a Lewis acid?

A

An electron pair acceptor

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4
Q

Does a ligand act as a Lewis acid or base?

A

Lewis base

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5
Q

Does a transition metal ion in a complex act as a Lewis acid or base?

A

Lewis acid

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6
Q

In a complex, what acts as the Lewis acid and what acts as the Lewis base?

A
  • ligand - Lewis base

* transition metal ion - Lewis acid

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7
Q

How do metal ions exist in aqueous solution?

A

As hexaaquaions

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8
Q

Which metal ions form 2+ hexaaquaions?

A

Cu2+ and Fe2+

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9
Q

Which metal ions form 3+ hexaaquaions?

A

Al3+ and Fe3+

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10
Q

Is the formation of hexaaquaions exo or endothermic? Why is this?

A

Exothermic as bonds are being formed

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11
Q

Is the formation of 2+ or 3+ hexaaquaions more exothermic? Why is this?

A

Formation of 3+ hexaaquaions because the bonds are stronger

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12
Q

What happens when a solution of hexaaquaions is evaporated?

A

Water of crystallisation - hexaaquaion remains intact as the coordinate bond between the water molecules and metal ion is so strong that they are not broken when the solution is evaporated

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13
Q

What colour is iron (II) sulphate in solution?

A

Green

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14
Q

What colour is iron (III) chloride in solution?

A

Violet

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15
Q

What colour is copper (II) nitrate in solution?

A

Blue

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16
Q

What colour is aluminium chloride in solution?

A

Colourless

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17
Q

In a hexaaqua ion, what are the types of bonds that could be broken?

A
  • coordinate

* covalent

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18
Q

What happens if the coordinate bond is broken in a hexaaqua ion?

A

Ligand substitution - water ligand is replaced by another ligand

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19
Q

What is hydrolysis?

A

When the O-H in the water molecule of a hexaaqua ion is broken

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20
Q

What effect does water have when it is added to a hexaaqua ion?

A

It strengthens the metal oxygen bond and the O-H bond weakens. Once the OH bond breaks a H⁺ ion is released from a H₂O ligand

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21
Q

What happens when the OH bond breaks in a hexaaqua ion?

A

A H⁺ ion is released from a H₂O ligand

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22
Q

What effect does the metal ion in a hexaaqua ion have on electron density in the ligands?

A

The positive charge pulls electron density away from O atom, and O is electronegative therefore pulls electron density away from H atom

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23
Q

What does the degree of acidity of a solution after hydrolysis depend on?

A

How many H₃O⁺ are formed

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24
Q

Where does the position of equilibrium for an M²⁺ hexaaquaion lie, and what does this mean for the acidity of the resulting solution?

A

Lies to left, so not many H₃O⁺ formed, so not very acidic

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25
Q

Where does the position of equilibrium for an M³⁺ hexaaquaion lie, and what does this mean for the acidity of the resulting solution?

A

Lies further right than M²⁺ ion, so solution contains more H₃O⁺ and so more acidic

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26
Q

How many M²⁺ ions are hydrolysed compared to M³⁺?

A
  • 1 in a million M²⁺
  • 1 in a thousand M³⁺

Therefore M³⁺ ions more acidic (but both cases solution is weakly acidic)

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27
Q

What are the factors that affect the degree of acidity of hexaaquaion hydrolysis solutions?

A
  • charge on the metal ion

* size of metal ion

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28
Q

Why does the charge on the metal ion and size affect the degree of acidity of solution after hydrolysis?

A

Metal centre is more polarising if charge is increased and size decreased as OH bond weakened to greater extent and more H⁺ formed

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29
Q

What can the two factors affecting the acidity of hydrolysis solutions be combined into?

A

Size to charge ratio (charge density)

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30
Q

What does size to charge ratio measure?

A

The polarising power of the ion i.e. ability to attract oppositely charged species

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31
Q

What effect does polarising power have on the acidity of the acidity of the hydrolysis solution?

A

↑ polarising power of metal ion = ↑ attraction for electrons from the O in the H₂O molecule - making OH bond weaker and easier to break - releasing H⁺ ions which form H₃O⁺ with water, increasing acidity

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32
Q

What is the formula for protonated water?

A

H3O⁺

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33
Q

Why are 3⁺ hexaaqua cations the most acidic in solution?

A

Greater charge to size ratio than 2+ so have greater polarising power and H₃O⁺ concentration and lower pH

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34
Q

When can further hydrolysis of aquaions take place?

A

When the H₃O⁺ is removed by the addition of a base

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35
Q

What bases can be used for further hydrolysis of aquaions?

A

OH⁻, NH₃, CO₃²⁻

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36
Q

What is the product of further hydrolysis?

A

The insoluble, neutral metal hydroxide

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37
Q

How is the product of further hydrolysis seen?

A

As a precipitate

38
Q

What effect does the base have on equilibrium for further hydrolysis of aquaions?

A

Pushes equilibrium right - base reacts with acid in neutralisation reaction, using acid up and reducing concentration of H₃O⁺

39
Q

What is the overall equation for the complete hydrolysis of M²⁺ ions?

A

[M(H₂O)₆]²⁺ + 2H₂O → [M(H₂O)₄(OH)₂] + 2H₃O⁺

40
Q

What is the overall equation for the complete hydrolysis of M³⁺ ions?

A

[M(H₂O)₆]³⁺ + 3H₂O → [M(H₂O)₃(OH)₃] + 3H₃O⁺

41
Q

Does further hydrolysis happen with water? Why?

A

No - it is not a strong enough base

42
Q

What reactions show how the hydroxide is precipitated during hydrolysis with sodium hydroxide?

A

[M(H₂O)₆]²⁺ + 2H₂O → [M(H₂O)₄(OH)₂] + 2H₃O⁺

2H₃O⁺ + 2OH⁻ → 4H₂O

(Then the H₃O⁺ react again with the OH⁻)

43
Q

Is the reaction of metalaquaions with sodium hydroxide ligand substitution?

A

No - it is hydrolysis instead

44
Q

What is the overall general equation for hydrolysis of a 2+ metalaquaion with sodium hydroxide?

A

[M(H₂O)₆]²⁺ + 2OH⁻ → [M(H₂O)₄(OH)₂] + 2H₂O

45
Q

How can reactions of metalaquaions with sodium hydroxide be reversed?

A

By adding a strong acid

46
Q

Why does adding a strong acid reverse hydrolysis between metalaquaions and sodium hydroxide?

A

The acid reacts with the OH⁻ to remove it, pushing the equilibrium to the left to replace it

47
Q

What equation can show why ammonia solution is a weak alkali?

A

NH3 + H2O → NH4⁺ + OH⁻

48
Q

What happens when a metalaquaion undergoes hydrolysis with ammonia solution?

A

The OH⁻ ions (from NH3 + H2O → NH4⁺ + OH⁻) precipitate the metal as its hydroxide in the same way as NaOH

49
Q

What is the general equation for a M²⁺ ion with NH₃ and the equations that add together to form this?

A

[M(H₂O)₆]²⁺ + 2OH⁻ → [M(H₂O)₄(OH)₂] + 2H₂O

2NH₃ + 2H₂O ⇋ 2NH₄⁺ + 2OH⁻

overall: [M(H₂O)₆]²⁺ + 2NH₃ → [M(H₂O)₄(OH)₂] + 2NH₄⁺

50
Q

What is the general equation for a M³⁺ ion with NH₃ and the equations that add together to form this?

A

[M(H₂O)₆]³⁺ + 3OH⁻ → [M(H₂O)₃(OH)₃] + 3H₂O

3NH₃ + 3H₂O ⇋ 3NH₄⁺ + 3OH⁻

overall: [M(H₂O)₆]³⁺ + 3NH₃ → [M(H₂O)₃(OH)₃] + 3NH₄⁺

51
Q

For the equation [M(H₂O)₆]²⁺ + 2NH₃ → [(H₂O)₄(OH)₂] + 2NH₄⁺, how has the ammonia been added?

A

Dropwise

52
Q

For the equation [M(H₂O)₆]³⁺ + 3NH₃ → [(H₂O)₃(OH)₃] + 3NH₄⁺, how has the ammonia been added?

A

Dropwise

53
Q

What happens if excess ammonia is added to the metal salt solution?

A

Ligand substitution will occur for Cu²⁺

54
Q

What is the equation for when excess ammonia is added to copper (II) salt solution?

A

[Cu(H₂O)₆]²⁺ + 4NH₃ → [Cu(NH₃)₄(H₂O)₂]²⁺ + 4H₂O

55
Q

Are carbonate ions weak or strong bases?

A

Weak

56
Q

What do carbonate ions react with acids to form?

A

Carbon dioxide and water

57
Q

Equation for reaction of carbonate ions with acid?

A

CO₃²⁻ + 2H₃O⁺ → CO₂ + 3H₂O

58
Q

What does the reaction of metal aqua ions with carbonates depend on?

A

The oxidation state of the metal ion

59
Q

What happens when carbonate ions react with M3+ metalaquaions?

A

There is sufficient H₃O⁺ to form carbon dioxide and water

60
Q

What is the general equation the reaction of carbonate ions with M3+ metalaquaions and the equations that add together to form this?

A

[M(H₂O)₆]³⁺ + 3H₂O ⇋ [M(H₂O)₃(OH)₃] + 3H₃O⁺ (x2)

CO₃²⁻ + 2H₃O⁺ → CO₂ + 3H₂O (x3)

overall: 2[M(H₂O)₆]³⁺ + 3CO₃²⁻ → 2[M(H₂O)₃(OH)₃] + 3CO₂ + 3H₂O

61
Q

Why can’t M2+ metalaquaions form carbon dioxide and water?

A

They are very weakly acidic in solution, so not enough acid (H₃O⁺)

62
Q

What do M2+ metalaquaions form when carbonate ions are added?

A

Insoluble metal carbonates (MCO₃)

63
Q

Equation for reaction of M2+ metalaquaions with carbonate ions?

A

[M(H₂O)₆]²⁺ + CO₃²⁻ → MCO₃ + 6H₂O

64
Q

Product and observation for reaction of [Cu(H₂O)₆]²⁺ with NaOH or NH₃ dropwise?

A

[Cu(H₂O)₄(OH)₂] - blue precipitate

65
Q

Product and observation for reaction of [Cu(H₂O)₆]²⁺ with NaOH in excess?

A

No change (so [Cu(H₂O)₄(OH)₂] - blue precipitate)

66
Q

Product and observation for reaction of [Cu(H₂O)₆]²⁺ with NH₃ in excess?

A

[Cu(NH₃)₄(H₂O)₂]²⁺ - deep blue solution

67
Q

Product and observation for reaction of [Cu(H₂O)₆]²⁺ with Na₂CO₃?

A

CuCO₃ - blue-green precipitate

68
Q

Product and observation for reaction of [Fe(H₂O)₆]²⁺ with NaOH or NH₃ dropwise?

A

[Fe(H₂O)₄(OH)₂] - green precipitate → if left to stand precipitate turns brown

69
Q

Product and observation for reaction of [Fe(H₂O)₆]²⁺ with NaOH in excess?

A

No change (so [Fe(H₂O)₄(OH)₂] - green precipitate that turns brown if left to stand)

70
Q

Product and observation for reaction of [Fe(H₂O)₆]²⁺ with NH₃ in excess?

A

No change (so [Fe(H₂O)₄(OH)₂] - green precipitate that turns brown if left to stand)

71
Q

Product and observation for reaction of [Fe(H₂O)₆]²⁺ with Na₂CO₃?

A

FeCO₃ - green precipitate

72
Q

Product and observation for reaction of [Fe(H₂O)₆]³⁺ with NaOH or NH₃ dropwise?

A

[Fe(H₂O)₃(OH)₃] - brown precipitate

73
Q

Product and observation for reaction of [Fe(H₂O)₆]³⁺ with NaOH in excess?

A

No change (so [Fe(H₂O)₃(OH)₃] - brown precipitate)

74
Q

Product and observation for reaction of [Fe(H₂O)₆]³⁺ with NH₃ in excess?

A

No change (so [Fe(H₂O)₃(OH)₃] - brown precipitate)

75
Q

Product and observation for reaction of [Fe(H₂O)₆]³⁺ with Na₂CO₃?

A

[Fe(H₂O)₃(OH)₃] - brown precipitate and effervescence

76
Q

Product and observation for reaction of [Al(H₂O)₆]³⁺ with NaOH or NH₃ dropwise?

A

[Al(H₂O)₃(OH)₃] - white precipitate

77
Q

Product and observation for reaction of [Al(H₂O)₆]³⁺ with NaOH in excess?

A

[Al(H₂O)₂(OH)₄] - colourless solution (further hydrolysis)

78
Q

Product and observation for reaction of [Al(H₂O)₆]³⁺ with NH₃ in excess?

A

[Al(H₂O)₃(OH)₃] - white precipitate

79
Q

Product and observation for reaction of [Al(H₂O)₆]³⁺ with Na₂CO₃?

A

[Al(H₂O)₃(OH)₃] - white precipitate and effervescence

80
Q

What is the amphoteric character of metal hydroxides?

A

The ability of metal hydroxides to react with both acids and alkalis

81
Q

How can the hydrolytic equilibrium reactions we’ve looked at be reversed?

A

Using a strong acid - the metal hydroxides dissolve to give the metal aqua ion

82
Q

What happens when strong acid is added to metal hydroxides?

A

They dissolve to give the metal aqua ion - reversing the hydrolysis

83
Q

What happens if excess HCl is added to a metal hydroxide solution?

A
  • Ligand substitution occurs with some of the metal hexaaqua ions (complete ligand substitution)
  • H₂O ligands are replaced by Cl, changing coordination number, shape, charge so changes colour
84
Q

When excess HCl is added to metal hydroxide solution, why does the solution change colour?

A

Some H₂O ligands are changed to Cl, changing coordination number, shape and charge

85
Q

When metal hydroxides react with acid, what do they act as?

A

Bases - proton acceptors

86
Q

What do metal hydroxides form when excess hydroxide is added?

A

Anionic complexes which are water soluble (further hydrolysis)

87
Q

Which metals undergo further hydrolysis?

A

Al

88
Q

When metal hydroxides react with alkalis, what happens to the H₂O ligands?

A

They donate a proton (H⁺) and therefore act as Bronsted-Lowry acids

89
Q

What is the equation for when aluminium hydroxide reacts with excess hydroxide?

A

[Al(H₂O)₃(OH)₃] + OH⁻ → [Al(H₂O)₂(OH)₄]⁻ + H₂O

90
Q

How do we know that further hydrolysis occurs when excess hydroxide is added to aluminium hydroxide?

A

The precipitate formed from the drowse addition dissolves in excess

91
Q

Why is it difficult to dissolve 2+ ions in alkali?

A

They are less acidic so would require a very concentrated alkaline solution

92
Q

What is a common example that shows amphoteric character and why is this?

A

Aluminium as it easily hydrolyses further

AQA A Level Inorganic Chemistry (6 decks)

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