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Chemistry A2 > Reactions of Inorganic Compounds in Aqueous Solution > Flashcards

Reactions of Inorganic Compounds in Aqueous Solution Flashcards

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1
Q

Explain why aqueous solution for M3+ is more acidic than M2+

A
  • higher charge density
  • more strongly polarising so attracts electrons from oxygen on water ligand
  • weakens OH bonds
  • increases tendency of complex ion to release H+
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2
Q

Give an equation to show hydrolysis of [Fe(H2O)6]3+

A

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

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

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3
Q

Lewis Acid

A

electron pair acceptor

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4
Q

Lewis Base

A

electron pair donor

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5
Q

Colour of [Fe(H2O)6]2+

A

pale green solution

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6
Q

Colour of [Fe(H2O)6]3+

A

pale purple solution

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7
Q

Explain why [Fe(H2O)6]3+ can appear yellow/brown

A
  • hydrolysis of [Fe(H2O)6]3+

- presence of [Fe(H2O)5OH]2+

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8
Q

Describe how to distinguish between Fe2+ (aq) and Fe3+ (aq) since they are both pale in colour

A
  • addition of base (NaOH)

- form coloured precipitates which are easily distinguishable

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9
Q

Give equation to show addition of base to M2+ (aq) to form metal hydroxide precipitate

A

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

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10
Q

Give equation to show addition of base to M3+ (aq) to form metal hydroxide precipitate

A

[M(H2O)6]3+ + 3OH- -> [M(H2O)3(OH)3] + 3H2O

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11
Q

Give colour of [Fe(H2O)4(OH)2] and explain why it turns brown on standing

A
  • green ppt

- some Fe2+ (aq) oxidises to Fe3+ (aq) which forms brown ppt of [Fe(H2O)3(OH)3]

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12
Q

Give equation to show acid-base reaction between M2+ (aq) and NH3 at low concentrations

A

[M(H2O)6]2+ + 2NH3 -> [M(H2O)4(OH)2] + 2NH4+

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13
Q

Give equation to show acid-base reaction between M3+ (aq) and NH3 at low concentrations

A

[M(H2O)6]3+ + 3NH3 -> [M(H2O)3(OH)3] + 3NH4+

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14
Q

Explain how acid-base reactions with CO32- can demonstrate relative acidity of M2+ (aq) and M3+ (aq)

A
  • M2+ produces metal carbonate only

- M3+ is acidic enough to produce CO2 gas from CO32-

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15
Q

Explain why carbonates of transition metals have an oxidation state of +2 but not +3

A
  • metal with oxidation state of +3 is acidic enough to liberate CO2 from CO32- so will not form carbonate with M3+
  • M2+ will form metal carbonate since it is less acidic
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16
Q

Give the intermediate stage and overall equation for reaction between M3+ (aq) and CO32-

A

[M(H2O)6]3+ + 3CO32- -> [M(H2O)3(OH)3] + 3HCO3-

2[M(H2O)6]3+ + 3CO32- -> 2[M(H2O)3(OH)3] + 3CO2 + 3H2O

17
Q

Give equation to show reaction between M2+ (aq) and CO32-

A

[M(H2O)6]2+ + CO32- -> MCO3 + 6H2O

18
Q

Colour of FeCO3 precipitate

A

green ppt

19
Q

Colour of [Al(H2O)6]3+

A

colourless solution

20
Q

Give equation to show addition of base to Al3+ (aq) and observations

A

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

white ppt of aluminium oxide formed

21
Q

Give equations to show how [Al(H2O)3(OH)3] behaves as an amphoteric hydroxide

A

[Al(H2O)3(OH)3] + 3H+ -> [Al(H2O)6]3+

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

22
Q

Give equation to show reaction between Al3+ (aq) and NH3 in low concentrations

A

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

23
Q

Explain why addition of base to Al3+ (aq) results in formation of white aluminium hydroxide precipitate but colourless solution in excess

A
  • formation of [Al(H2O)3(OH)3] to begin with which is white precipitate
  • [Al(H2O)3(OH)3] reacts with base to form [Al(OH)4]- which is colourless solution
24
Q

Explain why ligand substitution of H2O with NH3 occurs in transition metal complexes and why it occurs without a change in charge or oxidation number

A
  • NH3 is stronger ligand than H2O
  • N is more electronegative than O so more likely to donate electron pair to central metal ion
  • NH3 is same size and charge to H2O
25
Q

Give equation to show ligand substitution of H2O with NH3 in transition metal complex

A

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

26
Q

Give equations for two stage reaction of concentrated ammonia with M2+ (aq) and explain why this occurs

A

[M(H2O)6]2+ + 2OH- -> [M(H2O)4(OH)2] + 2H2O
[M(H2O)4(OH)2] + 6NH3 -> [M(NH3)6]2+ + 4H2O + 2OH-
- NH3- acts as a base so M2+ (aq) reacts with OH- from OH- in NH3 (aq) solution (NH3 + H2O -> NH4+ + OH-)
- excess NH3 acts as ligand and substitutes H2O

27
Q

Give equation to show (partial) ligand substitution of H2O with NH3 in Cu2+ (aq)

A

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

28
Q

Colour of [Cu(H2O)6]2+

A

pale blue solution

29
Q

Use equations to explain why Cu2+ forms a pale blue precipitate before a deep blue solution on addition of excess NH3

A
  • NH3 acts as base initially
    [Cu(H2O)6]2+ + 2OH- -> [Cu(H2O)4(OH)2] + 2H2O
  • NH3 acts ligand and partially substitutes H2O and OH- in excess
    [Cu(H2O)4(OH)2] + 4NH3 -> [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
30
Q

Describe structure of complex formed when Cu2+ (aq) reacts with excess NH3

A
  • distorted octahedral with 4 NH3 and 2 H2O ligands
  • NH3 form square planar arrangement
  • OH above and below plane
  • Cu-O bond is longer than Cu-N bond since H2O weaker ligand
31
Q

Colour of CuCO3

A

blue-green ppt

32
Q

Give equation and observations for reaction between Cu2+ (aq) and concentrated HCl

A

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

- pale blue solution changes colour to yellow-green solution

33
Q

Explain why there is a change in charge and coordination number for complex formed from reaction between Cu2+ (aq) and concentrated HCl

A
  • Cl- ligand has -1 charge where H2O ligand is neutral
  • Cl- ligand is larger than H2O so fewer can fit around Cu2+ ion
  • only four coordinate bonds form rather than six
34
Q

Explain why when NH4VO3 reacts with zinc under acidic conditions only two colour changes are observed

A

yellow>green>purple

  • VO2^+ (yellow) > VO2+ (blue) which appears green
  • remains green when reduced to V3+
  • then to purple when reduced to V2+

Chemistry A2 (12 decks)

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