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Chemistry A2 UNIT 5 > Inorganic Reactions > Flashcards

Inorganic Reactions Flashcards

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1
Q

METAL-AQUA IONS

A

When transition metal compounds dissolve in water, the water molecules form coordinate bonds with the metal ions. This forms metal aqua complex ions.

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2
Q

How many water molecules form coordinate bonds withe each metal ion in general?

A

6

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3
Q

How do water molecules form coordinate bonds?

A

They donate a non-bonding pair of electrons from their oxygen.

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4
Q

LEWIS ACID

A

electron pair acceptor

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5
Q

LEWIS BASE

A

electron pair donor

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6
Q

How do you tell if a reaction is a Lewis acid-base reaction?

A

If there is a coordinate bond- always involve one substance donating a pair of electrons to another.

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7
Q

Are metal ions Lewis acids or bases?

A

Metal ions are Lewis acids in aqueous solution because they accept electron pairs from the water molecules that surround them.

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8
Q

Are ligands Lewis acids or bases?

A

Lewis bases- electron pair donor

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9
Q

Why are solutions containing Metal-Aqua ions acidic?

A

In a solution containing metal aqua 2+ ions, there’s a reaction between the metal-aqua ion and the water- this is a hydrolysis or acidity reaction. e.g. [Fe(H2O)6]2+(aq) + H20(l) [Fe(H2O)5(OH)]+(aq) + H3O+(aq)

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10
Q

Why are solutions containing 2+ Metal-Aqua ions acidic?

A

In a solution containing metal aqua 2+ ions, there’s a reaction between the metal-aqua ion and the water- this is a hydrolysis or acidity reaction. e.g. [Fe(H2O)6]2+(aq) + H20(l) [Fe(H2O)5(OH)]+(aq) + H3O+(aq) The metal aqua 2+ ions release H+ ions, so an acidic solution is formed. There’s only slight dissociation though, so the solution is only weakly acidic. The metal aqua ion is acting as a Bronsted Lowry acid. It donates a proton from one of its water ligands to free a water molecule.

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11
Q

Why are solutions containing 3+ metal aqua ions more acidic than those with 2+ ions?

A

E.g. [Al(H2O)6]3+(aq) + H2O(l)[Al(H2O)5(OH)]2+ + H3O+(aq) Metal 3+ metal aqua ions are quite small but have a big charge- so they’ve got a high charge density (charge/size ratio). Metal 2+ ions have a much lower charge density. This makes the 3+ ions much more polarising than the 2+ ions. More polarising power means that they attract electrons from the oxygen atom of the coordinated water molecules more strongly, weakening the OH bond. So it’s more likely that hydrogen will be released. And more Hydrogen ions means a more acidic solution.

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12
Q

What does adding OH- ions to solutions of metal-aqua ions produce?

A

INSOLUBLE METAL HYDROXIDES

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13
Q

Why does adding OH- ions to a solution of metal-aqua ions produce insoluble metal hydroxides?

A

1) In water, metal-aqua 3+ ions form the equilibrium: [M(H2O)6]3+(aq) + H2O(l) [M(H2O)5(OH)]2+(aq) + H3O+(aq) If you add OH- ions to the equilibrium H3O+ ions are removed- shifts equilibrium to RIGHT. 2) Now another equilibrium is set up in the solution: [M(H2O)5(OH)]2+(aq) +H2O(l) [M(H2O)4(OH)2]+(aq) +H3O+(aq) Again the OH- ions remove H3O+ ions from the solution, pulling the equilibrium to the RIGHT.

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14
Q

What will the metal hydroxide precipitates dissolve in?

A

DISSOLVE IN ACID. They act as Bronsted Lowry bases and accept H+ions. This reverses hydrolysis reactions.

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15
Q

Some metal hydroxides are amphoteric, what does this mean and what does it allow them to do?

A

They act as both acids and bases. This means they will dissolve in an excess of base as well as in acids.

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16
Q

What are two examples of amphoteric metal hydroxides?

A

Act as Bronsted Lowry acids and donate H+ ions to the OH- ions, forming soluble compounds. ALUMINIUM HYDROXIDE: Al(H2O)3(OH)3(s) + OH-(aq) [Al(H2O)2(OH)4]-(aq) + H2O(l) CHROMIUM (III) HYDROXIDE: Cr(H2O)3(OH)3(s) +3OH- (aq) [Cr(OH)6]3-(aq) + 3H2O(l)

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17
Q

Describe how metal hydroxide precipitates are formed when ammonia is added.

A

Obvious way is using strong alkalis like NaOH- but you can use NH3 as well. When ammonia dissolves in water: NH3 + H2O NH4+ + OH- Because hydroxide ions are formed, adding a small amount of ammonia solution gives the same results a sNaOH

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18
Q

Describe how metal hydroxide precipitates are formed when ammonia is added.

A

Obvious way is using strong alkalis like NaOH- but you can use NH3 as well. When ammonia dissolves in water: NH3 + H2O NH4+ + OH- Because hydroxide ions are formed, adding a small amount of ammonia solution gives the same results as NaOH.

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19
Q

What happens if you add excess ammonia solution to a solution of metal aqua ions?

A

The H2O and OH- ligands are displaced by NH3 ligands.

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20
Q

What happens when metal 2+ ions react with sodium carbonate?

A

Form insoluble metal carbonates: [M(H2O)6]2+(aq) + CO32+(aq) MCO3(s) + 6H2O(l)

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21
Q

What happens when metal 3+ ions react with sodium carbonate?

A

Metal 3+ ions are stronger acids so they always form hydroxide precipitates when you add sodium carbonate. The carbonate ions react with the H3O+ ions, removing them from the solution.

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22
Q

What colour is [Co(H2O)6]2+?

A

PINK SOLUTION

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23
Q

What happens when OH- or NH3 is added to [Co(H2O)6]2+? Colou change and product.

A

Co(H2O)4(OH)2

BLUE GREEN PRECIPITATE

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24
Q

What happens when you add excess OH- to [Co(H2O)6]2+?

A

NO CHANGE FROM ADDING OH- or NH3

Blue green precipitate

Co(H2O)4(OH)2

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25
Q

What happens when you add excess NH3 to [Co(H2O)6]2+?

A

[Co(NH3)6]2+

STRAW COLOURED SOLUTION

26
Q

What happens when you react [Co(H2O)6]2+ with NaCO3?

A

CoCO3

PINK PRECIPITATE

27
Q

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

A

BLUE SOLUTION

28
Q

What happens to [Cu(H2O)6]2+ when you add OH- or NH3?

A

Cu(H2O)4(OH)2

BLUE PRECIPITATE

29
Q

What happens when you add ecess OH- to [Cu(H2O)6]2+?

A

Cu(H2O)4(OH)2

BLUE PRECIPITATE

30
Q

What happens when you add excess NH3 to [Cu(H2O)6]2+?

A

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

DEEP BLUE SOLUTION

31
Q

What happens when you add Na2CO3 to [Cu(H2O)6]2+?

A

CuCO3

GREEN BLUE PRECIPITATE

32
Q

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

A

GREEN SOLUTION

33
Q

What happens when you add OH- or NH3 to [Fe(H2O)6]2+?

A

Fe(H2O)4(OH)2

GREEN PRECIPITATE

34
Q

WHat happens when you add excess OH- to [Fe(H2O)6]2+?

A

Fe(H2O)4(OH)2

GREEN PRECIPITATE

35
Q

What happens when you add excess NH3 to [Fe(H2O)6]2+?

A

Fe(H2O)4(OH)2

GREEN PRECIPITATE

36
Q

What happens when you add Na2CO3 to [Fe(H2O)6]2+?

A

FeCO3

GREEN PRECIPITATE

37
Q

What colour is [Al(H2O)6]3+?

A

COLOURLESS SOLUTION

38
Q

What happens when you add OH- or NH3 to [Al(H2O)6]2+?

A

Al(H2O)3(OH)3

WHITE PRECIPITATE

39
Q

What happens when you add excess OH- to [Al(H2O)6]2+?

A

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

COLOURLESS SOLUTION

40
Q

What happens when you add excess NH3 to [Al(H2O)6]3+?

A

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

COLOURLESS SOLUTION

41
Q

What happen when you add Na2CO3 to [Al(H2O)6]3+?

A

Al(H2O)3(OH)3

WHITE PRECIPITATE

42
Q

What colour is [Cr(H2O)6]2+?

A

VIOLET SOLUTION

43
Q

What happens when you add OH- or NH3 to [Cr(H2O)6]3+?

A

Cr(H2O)3(OH)3

GREEN PRECIPITATE

44
Q

What happens when you add excess OH- to [Cr(H2O)6]2+?

A

[Cr(OH)6]3-

GREEN SOLUTION

45
Q

What happens when you add excess NH3 to [Cr(H2O)6]3+?

A

[Cr(NH3)6]3+

PURPLE SOLUTION

46
Q

What happens when you add Na2CO3 to [Cr(H2O)6]3+?

A

Cr(H2O)3(OH)3

GREEN PRECIPITATE

47
Q

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

A

YELLOW SOLUTION

48
Q

What happens when you add OH- or NH3 to [Fe(H2O)6]3+?

A

Fe(H2O)3(OH)3

BROWN PRECIPITATE

49
Q

What happens when you add excess OH- to [Fe(H2O)6]3+?

A

Fe(H2O)3(OH)3

BROWN PRECIPITATE

50
Q

What happens when you add excess NH3 to [Fe(H2O)6]3+?

A

Fe(H2O)3(OH)3

BROWN PRECIPITATE

51
Q

What happens when you add Na2CO3 to [Fe(H2O)6]3+?

A

Fe(H2O)3(OH)3

BROWN PRECIPITATE

52
Q

LIGAND EXCHANGE

A

One ligand can be swapped for another ligand, almost always causes a colour change.

53
Q

What happens if a ligand is swapped with one of a similar size? Examples.

A

If the ligands are of similare size, e.g. H2O and NH3, then the coordinaton number of the complex ion doesn’t change, and neither does the shape.

[Co(H2O)6]2+(PINK octahedral) + 6NH3 -> [Co(NH3)6]2+ (OCTAHEDRAL STRAW COLOUR)+6H2O

Cr(H2O)6]3+(Octahedral violet) + 6OH- -> [Cr(OH)6]3- (Octahedral green) + 6H2O

54
Q

What happens if the ligands are different sizes? EXAMPLES

A

E.g. H2O and Cl-. there’s a change of coordination number and a change of shape.

[Cu(H2O)6]2+ (octahedral blue) + 4Cl- [CuCl4]2- (tetrahedral yellow) +6H2O

[Co(H2O)6]2+ (Octahedral pink) + 4Cl- [CoCl4]2- (tetrahedrl blue) +6H2O

55
Q

Give two examples of partial substitution.

A

[Cu(H2O)6]2+ (octahedral pale blue) + 4NH3 -> [Cu(NH3)4(H2O)2]2+(elongated octahedral deep blue) + 4H2O

[Fe(H2O)6]3+(octahedral pale violet when pure) + SCN- -> [Fe(H2O)5SCN]2+(destorted octahedral blood red) +H2O

56
Q

When can ligand exchange reactions not be easily reversed?

A

Unless the new complex ion is much more stable than the old one.

57
Q

What complexes are stronger?

A

Multidentate ligands form more stable complexes then unidentate ligands.

58
Q

What happens when a ligand exchange reaction occurs?

A

Bonds are broken and formed.

The strength of the bonds being broken is often very similar to the strength of the new bonds beng made.

So the enthalpy change for a ligand exchange is usually very small.

59
Q

What happens when unidentate ligands are substituted with bidentate or multidentate ligands? (CHELATE EFFECT)

A

The number of particles increases- the more particles, the greater the entropy. Reactions that result in an increase in entropy are more likely to occur. This is known as the chelate effect.

60
Q

Why is it diffiult to reverse reactions when unidentate ligand is substituted with a multidentate ligand?

A

Decrease in entropy.

Chemistry A2 UNIT 5 (5 decks)

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