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Chemistry > 24. Reactions of inorganic compounds in aqueous solutions > Flashcards

24. Reactions of inorganic compounds in aqueous solutions Flashcards

1
Q

What is an aqua ion

A

When a transition metal forms a complex ion with 6 water molecules as ligands

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2
Q

Why is a solution of Fe3+ acidic and Fe2+ not

A
  • Fe3+ ion is smaller and more highly charged than Fe2+
  • it is therefore more strongly polarising
  • in the [Fe(H2O)6] 3+ (aq) ion the iron strongly attracts electrons from the oxygen atoms
  • weakening O-H bonds in the water molecules
  • this complex ion will then readily release an H+ ion
  • Fe2+ is less polarising so fewer O-H bonds break in solution
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3
Q

What is a hydrolysis reaction

A

A reaction in which O-H bonds of water are broken and new species are formed

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4
Q

Write an equation for the hydrolysis of [Fe(H2O)6] 3+

A

[Fe(H2O)6] 3+ (aq) + H2O (l) —-> [Fe(H2O)5(OH)] 2+ (aq) + H3O+ (aq)

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5
Q

The reaction of [Fe(H2O)6] 3+ releasing H+ ions can be described as what reaction

A

Hydrolysis

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6
Q

Write an equation for the release of H+ ions from [Fe(H2O)6] 3+

A

[Fe(H2O)6] 3+ (aq)—-> [Fe(H2O)5(OH)] 2+ (aq) + H+ (aq)

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7
Q

In the reaction [Fe(H2O)6] 3+ (aq) + H2O (l) —-> [Fe(H2O)5(OH)] 2+ (aq) + H3O+ (aq) what is the Fe3+ complex acting as

A

A Bronsted Lowry acid as it is donating a proton (H+) to a water molecule

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8
Q

What are the two examples of [M(H2O)6] 3+

A

[Fe(H2O)6] 3+

[Al(H2O)6] 3+

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9
Q

What are the two examples of [M(H2O)6] 2+

A

[Fe(H2O)6] 2+

[Cu(H2O)6] 2+

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10
Q

What happens if you add a base (e.g OH-) to a M2+ or M3+ aqueous complex

A

It will remove protons from the aqueous complex

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11
Q

What happens if you add a base (e.g OH-) to a M3+ aqueous complex

A

[M(H2O)6] 3+ (aq) + OH- (aq) —> [M(H2O)5(OH)] 2+ (aq) + H2O (l)
[M(H2O)5(OH)] 2+ (aq) + OH- (aq) —> [M(H2O)4(OH)2] + (aq) + H2O (l)
[M(H2O)4(OH)2] + (aq) + OH- (aq) —-> M(H2O)3(OH)3 (s) + H2O
It becomes a neutral metal (III) hydroxide precipitate

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12
Q

What happens if you add a base (e.g OH-) to a M2+ aqueous complex

A

[M(H2O)6] 2+ (aq) + OH- (aq) —> [M(H2O)5(OH)] + (aq)
+ H2O (l)
[M(H2O)5(OH)] + (aq) + OH- —> M(H2O)4(OH)2 (s) + H2O (l)
It becomes a neutral metal (II) hydroxide precipitate

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13
Q

What is the precipitate formed when a base (OH-) is added to a M3+ aqueous complex

A

M(H2O)3(OH)3

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14
Q

What is the precipitate formed when a base (OH-) is added to a M2+ aqueous complex

A

M(H2O)4(OH)2

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15
Q

Why does iron (III) carbonate not exist but iron (II) carbonate does

A
  • because Fe3+ (aq) is more acidic than Fe2+ (aq)
  • carbonate ion is able to remove protons from [Fe(H2O)6] 3+ to form hydrated iron (III) hydroxide
  • cannot do this with [Fe(H2O)6] 2+
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16
Q

What is the overall equation for the reaction between iron (III) aqua complex and carbonate ions

A

2[Fe(H2O)6] 3+ (aq) + 3CO3 2- (aq) —-> 2[Fe(H2O)3(OH)3] (aq) + 3CO2 (g) + 3H2O

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17
Q

What is the overall equation for the reaction between iron (II) aqua complex and carbonate ions

A

[Fe(H2O)6] 2+ (aq) + CO3 2- (aq) —-> FeCO3 (s) +6H2O

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18
Q

What is the general rule for the formation of carbonates with M2+ and M3+ aqua complexes

A

In general, carbonates of transition metal ions in oxidation state 2+ exist, whilst those of ions in the +3 state do not

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19
Q

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

A

pale green

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20
Q

What is the colour of [Fe(H2O)6] 3+

A

pale brown

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21
Q

Describe a test to distinguish [Fe(H2O)6] 2+ and [Fe(H2O)6] 3+

A
  • add dilute alkali to both
  • the precipitates of both of these complexes are far more distinguishable
  • Fe(H2O)3(OH)3 (s) is brown
  • Fe(H2O)4(OH)2 is green
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22
Q

What does amphoteric mean

A

Showing both acidic and basic properties and can react with both acids and bases

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23
Q

What is an example of an amphoteric hydroxide

A

Aluminium hydroxide

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24
Q

Write an equation for the reaction between HCl and Al(H2O)3(OH)3

A

Al(H2O)3(OH)3 + 3HCl —> Al(H2O)6 3+ + 3Cl-

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25
Q

Write an equation for the reaction between OH- and Al(H2O)3(OH)3

A

Al(H2O)3(OH)3 + OH- —-> [Al(H2O)2(OH)4]- + H2O

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26
Q

Name two reasons other ligands would replace water ligands in an aqua ion complex

A
  • the other ligand forms stronger co-ordinate bonds

- the other ligand are present in higher concentration and equilibrium is displaced

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27
Q

List the properties of things that can replace water as a ligand

A
  • water molecules may be replaced by other neutral ligands (e.g ammonia)
  • water molecules may be replaced by negatively charged ligands, such as chloride ions
  • water molecules may be replaced by bi-or multidentate ligands (chelation)
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28
Q

What happens when a M2+ aqua ion by ammonia

A
  • water molecules are replaced one at a time by ammonia
  • [M(H2O)6] 2+ +NH3 —–> [M(NH3)(H2O)5] 2+ + H2O
  • [M(NH3)(H2O)5] 2+ + NH3 —-> [M(NH3)2(H2O)4] 2+ H2O
  • and so on until
  • [M(NH3)6] 2+ is formed
29
Q

Write the overall equation for the reaction of

[M(H2O)6] 2+ and ammonia

A

[M(H2O)6] 2+ + 6NH3 [M(NH3)6] 2+ + 6H2O

30
Q

What is the complication in the reaction between [M(H2O)6] 2+ and ammonia

A
  • ammonia is a base as well a ligand
  • so the OH- ions that are in ammonia (aq) might react with the [M(H2O)6] 2+
  • a precipitate might form and dissolve
31
Q

Write the reaction where ammonia reacts as a base with [M(H2O)6] 2+

A

[M(H2O)6] 2+ (aq) + 2OH- (aq) —> M(H2O)4(OH)2 (s) + 2H2O

M(H2O)4(OH)2 (s) + 6NH3 (aq) —-> [M(NH3)6] 2+ (aq) +4H2O (l) + 2OH- (aq)

32
Q

Write the equation for the reaction of [Co(H2O)6] 2+ and ammonia (conc.)

A

[Co(H2O)6] 2+ (aq) + 2NH3 (aq) —> Co(H2O)4(OH)2 + 2NH4+ (aq)
-here ammonia is acted as a base

33
Q

What is the colour of the precipitate formed when ammonia reacts as a base with [Co(H2O)6] 2+

34
Q

Write an equation if you add more excess ammonia to the products of the reaction between [Co(H2O)6] 2+ and ammonia (conc.)

A

Co(H2O)4(OH)2 (s) + 6NH3 (aq) —> [Co(NH3)6] 2+ (aq)

4H2O (l) + 2OH- (aq)

35
Q

Why does ammonia replace water as ligands in Co(H2O)4(OH)2 (s)

A
  1. ammonia is a better ligand than water

2. high concentration of ammonia displaces equilibria (displacing both (OH- and H2O))

36
Q

Describe the observations in the reaction between [Co(H2O)6] 2+ and ammonia

A

First blue ppt. which then dissolves to form a pale yellow solution.

37
Q

When aqueous copper ions react with ammonia in aqueous solution ligand replacement is only…

38
Q

How many ligands are replace when aqueous copper ions react with ammonia in aqueous solution

39
Q

What is the overall reaction between aqueous copper ions react with ammonia in aqueous solution

A

[Cu(H2O)6] 2+ + 4NH3 —> [Cu(NH3)4(H2O)2] 2+ + 4H2O

-here ammonia is acting as a base

40
Q

What is the colour of [Cu(H2O)6] 2+ and [Cu(NH3)4(H2O)2] 2+

A

[Cu(H2O)6] 2+ is pale blue

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

41
Q

What happens in the reaction between ammonia and [Cu(H2O)6] 2+

A
  • ammonia first acts as a base
  • the precipitate [Cu(OH)2(H2O)4] (s) is produced
  • which is pale blue ppt.
  • when more ammonia is added the ppt. dissolves to form [Cu(NH3)4(H2O)2] 2+ (deep blue)
42
Q

Write the equation for when the ppt. [Cu(OH)2(H2O)4] dissolves in ammonia

A

[Cu(OH)2(H2O)4] (s) + 4NH3 (aq) [Cu(NH3)4(H2O)2] 2+ (aq) + 2H2O (l) + 2OH- (aq)

43
Q

What is the shape of [Cu(NH3)4(H2O)2] 2+

A
  • octahedral (as expected for six co-ordinate ion)

- the 4 ammonia molecules exist in square planar

44
Q

When aqueous copper ions react with concentrated hydrochloric acid there is a change in both…

A
  • charge

- co-ordination number

45
Q

Write the equation for the reaction between chloride ions and [Cu(H2O)6] 2+

A

[Cu(H2O)6] 2+ + 4Cl- —> [CuCl4] 2- + 6H2O

46
Q

What is the colour of [CuCl4] 2-

47
Q

Why does [Cu(H2O)6] 2+ have coordination number six and become [CuCl4] 2- with coordination number of only 4

A

Cl- is larger than H2O so fewer ligands can physically fit around the central copper ion

48
Q

What is chelation

A

Formation of complexes with multidentate ligand

49
Q

What are multidentate ligands

A

Ligands with more than one lone pair so they can form more than one co-ordinate bond

50
Q

Give 3 examples of multidentate ligands

A
  • ethylene diamine
  • benzene- 1,2-diol
  • EDTA 4-
51
Q

Why are complexes usually more stable with multidentate ligands than monodentate ligands

A

There is a positive entropy change of the reaction

52
Q

What can ethylene diamine be represented as

53
Q

Write the equation for the reaction between en and [Cu(H2O)6] 2+

A

[Cu(H2O)6] 2+ (aq) + 3en —> [Cu(en)3] 2+ (aq) + 6H2O

4 entities to 7 meaning big increase in entropy

54
Q

Write the equation for the reaction between en and [Cu(H2O)6] 2+ (aq) and EDTA 4-

A

[Cu(H2O)6] 2+ (aq) + EDTA 4- (aq) —-> [CuEDTA] 2- (aq) + 6H2O

55
Q

Reaction between OH- and [Fe(H2O)6] 2+ (aq)

A
  • green ppt.

- [Fe(H2O)4(OH)2]

56
Q

Reaction between OH- and [Cu(H2O)6] 2+ (aq)

A
  • pale blue ppt.

- [Cu(H2O)4(OH)2]

57
Q

Reaction between NH3 and [Fe(H2O)6] 2+ (aq)

A
  • green ppt.

- [Fe(H2O)4(OH)2]

58
Q

Reaction between little NH3 and [Cu(H2O)6] 2+ (aq)

A
  • pale blue ppt.

- [Cu(H2O)4(OH)2]

59
Q

Reaction between excess NH3 and [Cu(H2O)6] 2+ (aq)

A
  • deep blue solution

- [Cu(NH3)4(H2O)2] 2+

60
Q

Reaction between CO3 2- and [Fe(H2O)6] 2+ (aq)

A
  • green ppt.

- FeCO3

61
Q

Reaction between CO3 2- and [Cu(H2O)6] 2+ (aq)

A
  • green/blue ppt.

- CuCO3

62
Q

Reaction between OH- and [Fe(H2O)6] 3+ (aq)

A
  • brown ppt.

- [Fe(H2O)3(OH)3]

63
Q

Reaction between little OH- and [Al(H2O)6] 3+ (aq)

A
  • white ppt.

- [Al(H2O)3(OH)3]

64
Q

Reaction between excess OH- and [Al(H2O)6] 3+ (aq)

A
  • colourless

- [Al(OH)4-]

65
Q

Reaction between NH3 and [Fe(H2O)6] 3+ (aq)

A
  • brown ppt.

- [Fe(H2O)3(OH)3]

66
Q

Reaction between NH3 and [Al(H2O)6] 3+ (aq)

A
  • white ppt.

- [Al(H2O)3(OH)3]

67
Q

Reaction between CO3 2- and [Fe(H2O)6] 3+ (aq)

A
  • brown ppt.
  • [Fe(H2O)3(OH)3]
  • and CO2 bubbles
68
Q

Reaction between CO3 2- and [Al(H2O)6] 3+ (aq)

A
  • white ppt.
  • [Al(H2O)3(OH)3]
  • and bubbles of CO2

Chemistry (27 decks)

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