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Chemistry Year 12 > Reactions of Ions in Aqueous Solution 3.2.6 > Flashcards

Reactions of Ions in Aqueous Solution 3.2.6 Flashcards

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1
Q

How are metal-aqua complexes formed

A

When we add a transition metal compound to water

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2
Q

what are metal aqua ions in solution .

A

Acidic in solution
The charge of the ion has an effect on how acidic it is

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3
Q

What are 2 generic examples of acidity or hydrolysis reactions

A

[M(H2O)6]2+ + H2O (reverse sign) [M(H2O)5(OH)]+ + H3O+

[M(H2O)6]3+ + H2O (reverse sign) [M(H2O)5(OH)]2+ + H3O+

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4
Q

Why are [M(H2O)6] 3+ more acidic than [M(H2O)6] 2+

A

• +3 metal ions have a higher charge density than 2+ ions . This is because they have a larger charge and they’re small
• +3 metal ions are more polarising . This means that they attract electrons in the O-H bond in the water ligands more strongly
• This weakens O-H bond so it breaks more easily releasing H+ ions

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5
Q

Why are [M(H2O)6] 3+ more acidic than [M(H2O)6] 2+

A

• +3 metal ions have a higher charge density than 2+ ions . This is because they have a larger charge and they’re small
• +3 metal ions are more polarising . This means that they attract electrons in the O-H bond in the water ligands more strongly
• This weakens O-H bond so it breaks more easily releasing H+ ions

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6
Q

Where does equilibrium lie when we add OH- ions to a hydrolysis reaction of metal aqua ions

A

If we add OH- they remove H3O+ and equilibrium shifts to the right

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7
Q

How can we hydrolyse a metal aqua ion further

A

Use OH- ions to make insoluble metal hydroxides

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8
Q

what are the equations on further hydrolysing a metal aqua ion using OH- to form a neutral complex that is solid and forms a precipitate in solution for +3 ions

A

Start from :
[M(H2O)6]3+ (aq) + H2O(l) (reverse sign) [M(H2O)5(OH)]2+ (aq) + H3O+ (aq)

Further hydrolysed to :

[M(H2O)5(OH)]2+ (aq) + H2O(l) (reverse sign) [M(H2O)4(OH)2]+ (aq) + H3O+ (aq)

Further hydrolysed to :

[M(H2O)4(OH)2]+ (aq) + H2O(l) (reverse sign) M(H2O)3(OH)3 (s) + H3O+ (aq)

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9
Q

what are the equations for further hydrolysis of metal aqua ions using OH- to form a neutral , insoluble solid complex from 2+ metal aqua ions

A

Start from :
[M(H2O)6]2+ (aq) +H2O(l) (reverse sign) [M(H2O)5(OH)]+ (aq) +H3O+ (aq)

further hydrolyse to :

[M(H2O)5(OH)]+ (aq) +H2O(l) (reverse sign) M(H2O)4(OH)2 (s) +H3O+ (aq)

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10
Q

what does amphoteric mean and what’s an example

A

Metal hydroxides can act as an acid or a base

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11
Q

what does it mean when metal hydroxides are amphoteric

A

Will dissolve in both excess acid and base

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12
Q

how can we reverse the reaction of amphoteric metal hydroxides precipitates

A

Add an acid (H+ ions) to the metal hydroxide precipitate and it will dissolve .
They do this by accepting a H+ ion and are bronsted lowry bases

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13
Q

what’s an example of an amphoteric metal hydroxide

A

Aluminium hydroxide Al(H2O)3(OH)3

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14
Q

what happens when we add a base to aluminium hydroxide (amphoteric molecule)

A

It acts as a bronsted lowry acid and donates H+ ions to react with the OH- and it dissolves

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15
Q

what’s the reaction of adding a base to aluminium hydroxide (amphoteric)

A

Al(H2O)3(OH)3 (s) + OH- (aq) => [Al(H2O)2(OH)4]- (aq) + H2O(aq)

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16
Q

what happens when we add an acid to aluminium hydroxide (amphoteric)

A

It acts as a bronsted lowry base by accepting H+ ions to form H3O+ in solution and dissolves

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17
Q

what’s the reaction of adding an acid to aluminium hydroxide (amphoteric )

A

Al(H2O)3(OH)3 (s) + 3H+ (aq) => [Al(H2O)6] 3+ (aq)

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18
Q

what happens when we add ammonia to metal aqua ions

A

They form metal hydroxide precipitates

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19
Q

what happens when we add excess ammonia to metal aqua ions

A

A ligand substitution reaction occurs

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20
Q

what’s the reaction of Cu(OH)2(H2O)4 when excess ammonia is added

A

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

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21
Q

whats the reaction when you add a 2+ metal aqua ion complex with a small amount of ammonia

A

[M(H2O)6]2+ (aq) + 2NH3(aq) => M(H2O)4 (OH2) (s) + 2NH4+ (aq)

22
Q

whats the reaction when you add a small amount of ammonia to a 3+ metal aqua complex

A

[M(H2O)6]3+ (aq) + 3NH3(aq) => Fe(H2O)3(OH)3 (s) + 3NH4+ (aq)

23
Q

what happens when you add sodium carbonate to a 2+ metal aqua ion

A

forms metal carbonates precipitates

24
Q

what’s the reaction of adding carbonates to a 2+ metal aqua ions

A

[M(H2O)6]2+ (aq) + CO2 3- (aq) (reverse sign) MCO3(s) + 6H2O(l)

25
Q

what’s the reaction with carbonates and a 3+ metal aqua ions

A

2 [M(H2O)6]3+ (aq) + 3CO3 2- (aq) (reverse sign) 2M(OH)3(H2O)3 (s) + 3CO2 (g) + 3 H2O (l)

26
Q

How do we perform test tube reactions to identify metal ion solutions

A

1) add a sample of the unknown metal ion solution into 3 test tubes
2) Drop by drop add NaOH to tube 1 and observe any changes .
Then add more to see if excess NaOH results in a further change .
3) Repeat step 2 except use ammonia solution in test tube 2
4) In tube 3 add sodium carbonate solution Na2CO3

27
Q

what is the observation when you add NaOH and excess NaOH to aluminium hydroxide

A

Al3+ ions in solution + NaOH = Precipitate formed
Add excess NaOH = precipitate dissolves

28
Q

what’s the observation when you add NH3 and NH3 in excess to copper hydroxide

A

Cu2+ ions in solution + NH3 = precipitate formed
Add excess NH3 = precipitate dissolves dark blue colour formed

29
Q

What is the observation with Al3+ and Fe3+ (3+ metal ions) reacting with carbonates

A

Form a precipitate and carbon dioxide so bubbles will be observed

30
Q

what’s the observation with Cu2+ and Fe2+ (2+ metal ions) reacting with carbonates

A

forms a precipitate only

31
Q

why do solutions of Fe2+ forming Fe3+ need to be made fresh

A

Because Fe2+ oxidises readily with air to form Fe3+

32
Q

what’s the colour of Cu2+ in aqueous solution

A

Blue

33
Q

what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Cu2+

A

Pale blue precipitate

34
Q

what’s the colour when you add excess NH3 to the precipitate of Cu2+

A

Dark blue solution

35
Q

what’s the colour when you add Na2CO3 to Cu2+

A

Green blue precipitate

36
Q

what’s the colour when you add excess OH- to the precipitate of Cu2+

A

Insoluble in excess NaOH
(no change )

37
Q

what’s the colour of Fe2+ in aqueous solution

A

Pale green

38
Q

what’s the colour of Fe3+ in aqueous solution

A

Yellow

39
Q

what’s the colour of Al3+ in aqueous solution

A

Colourless

40
Q

what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Fe2+

A

Dirty Green precipitate

41
Q

what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Fe3+

A

Orange precipitate

42
Q

what’s the colour when you add small amount of OH- or NH3 to aqueous solution of Al3+

A

White precipitate

43
Q

what’s the colour when you add excess OH- to the precipitate of Fe2+

A

Insoluble in excess NaOH
(No change)

44
Q

what’s the colour when you add excess OH- to the precipitate of Fe3+

A

Insoluble in excess NaOH
(No change)

45
Q

what’s the colour when you add excess OH- to the precipitate of Al3+

A

Colourless solution

46
Q

what’s the colour when you add excess NH3 to the precipitate of Fe2+

A

Insoluble in excess NH3
(No change)

47
Q

what’s the colour when you add excess NH3 to the precipitate of Fe3+

A

Insoluble in excess NH3
(no change)

48
Q

what’s the colour when you add excess NH3 to the precipitate of Al3+

A

No change

49
Q

what’s the colour when you add Na2CO3 to Fe2+

A

Green precipitate

50
Q

what’s the colour when you add Na2CO3 to Fe3+

A

Brown precipitate

51
Q

what’s the colour when you add Na2CO3 to Al3+

A

white precipitate

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