Reactions of aqueous ions Flashcards

1
Q

What is meant by enthalpy of hydration?

A
  • standard enthalpy change
  • when one mole of gaseous ions
  • covered into one mole of aqueous ions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

enthalpy of hydration is…

A
  • always exothermic
  • bonds made with water molecules
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a co-ordinate bond?

A
  • shared pair of electrons
  • that have come from the same atom
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a ligand?

A
  • ion/molecule with lone pair of electrons
  • forms co-ordinate bond with transition metal ion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a complex ion?

A

central atom/ion surrounded by ligands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the co-ordination number?

A

number of co-ordinate bonds formed by transition metal ion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the 4 hexa aqua ions?

A

[Fe(H2O)6] 2+

[Fe(H2O)6] 3+

[Cu(H2O)6] 2+

[Al(H2O)6] 3+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What colour solution does Cu 2+ give when hydrated?

A

[Cu(H2O)6] 2+ (aq)
Blue solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What colour solution does Fe 2+ give when hydrated?

A

[Fe(H2O)6] 2+ (aq)
Pale green solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What colour solution does Fe 3+ give when hydrated?

A

[Fe(H2O)6] 3+ (aq)
Purple solution
may look yellow/brown

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What colour solution does Al 3+ give when hydrated?

A

[Al(H2O)6] 3+ (aq)
Colourless solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why are the 3+ ions more acidic?

A
  • Fe3+ smaller and more highly charged than Fe2+
  • so Fe3+ more polarising
  • Fe3+ attracts LP on oxygen of water ligands more strongly
  • weakens O-H bond strength
  • Fe3+ complex more easily releases H+
  • Fe2+ does not release H+
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the equation which represents [Fe(H2O)6] 3+ acting as an acid?

A

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

OR

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the equation which represents [Al(H2O)6] 3+ acting as an acid?

A

[Al(H2O)6] 3+ —> [Al(H2O)5(OH)] 2+ + H+

OR

[Al(H2O)6] 3+ + H2O —> [Al(H2O)5(OH)] 2+ + H3O+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Reaction of [Fe(H2O)6] 2+ with Na2CO3

A

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

green solution becomes green ppt FeCO3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Reaction of [Fe(H2O)6] 2+ with NaOH

A

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

green solution becomes green ppt [Fe(H2O)4(OH)2] (s)

  • green ppt goes brown on standing in air
  • oxygen oxidises Fe2+ to Fe3+
17
Q

Reaction of [Fe(H2O)6] 2+ with NH3

A

[Fe(H2O)6] 2+ + 2NH3 —> [Fe(H2O)4(OH)2] (s) + 2NH4+

  • green solution becomes green ppt [Fe(H2O)4(OH)2] (s)
  • green ppt goes brown on standing in air
  • oxygen oxidises Fe2+ to Fe3+
18
Q

Reaction of [Cu(H2O)6] 2+ with Na2CO3

A

[Cu(H2O)6] 2+ + CO3 2- —> CuCO3 (s) + 6H2O

  • blue solution becomes blue/green ppt
19
Q

Reaction of [Cu(H2O)6] 2+ with NaOH

A

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

  • blue solution becomes blue ppt [Cu(H2O)4(OH)2] (s)
20
Q

Reaction of [Cu(H2O)6] 2+ with NH3

A

[Cu(H2O)6] 2+ + 2NH3 —> [Cu(H2O)4(OH)2] (s) + 2NH4+

  • blue solution becomes blue ppt
21
Q

Reaction of [Cu(H2O)6] 2+ in excess NH3

A

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

  • blue solution becomes deep blue solution [Cu(H2O)2(NH3)4] 2+ (aq)

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

  • blue solution becomes deep blue solution [Cu(H2O)2(NH3)4] (aq)
22
Q

Reaction of [Cu(H2O)6] 2+ with HCl

A

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

  • blue solution —> yellow solution [CuCl4] 2- (aq)
  • complex changes from octahedral to tetrahedral
23
Q

Reaction of [Fe(H2O)6] 3+ with Na2CO3

A

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

yellow/brown solution —> brown ppt and effervescence
- CO2 gas evolved

24
Q

Reaction of [Fe(H2O)6] 3+ with NaOH

A

[Fe(H2O)6] 3+ + 3OH- —> Fe(H2O)3(OH)3] (s) + 3H2O
yellow/brown solution —> brown ppt

25
Q

Reaction of [Fe(H2O)6] 3+ with NH3

A

[Fe(H2O)6] 3+ + 3NH3 —> [Fe(H2O)3(OH)3] + 3NH4+
yellow/brown solution —> brown ppt

26
Q

Reaction of [Al(H2O)6] 3+ with Na2CO3

A

2 [Al(H2O)6] 3+ + 3CO3 2- —> 2[Al(H2O)3(OH)3] (s) + 3CO2 + 3H2O

colourless solution —> white ppt and effervescence

27
Q

Reaction of [Al(H2O)6] 3+ with NaOH

A

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

colourless solution —> white ppt [Al(H2O)3(OH)3] (s)

28
Q

Reaction of [Al(H2O)6] 3+ with excess NaOH

A

[Al(H2O)6] 3+ + OH- —> [Al(H2O)2(OH)4] - (s) + H2O

white ppt dissolves to colourless solution

29
Q

Reaction of [Al(H2O)6] 3+ with NH3

A

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

colourless solution —> white ppt

30
Q

Show how aluminium hydroxide is amphoteric when HCl is added

A

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

acts as a base

31
Q

Show how aluminium hydroxide is amphoteric when NaOH is added

A

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

acts as an acid

32
Q

Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has
a pH ˂7

A

[Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)] 2+ + H+

  • Al 3+ has small size and high charge
  • weakens OH bond releasing H+ ions
33
Q

Reaction of [Fe(H2O)6] 2+ with excess NH3

A

No further change

34
Q

Reaction of [Fe(H2O)6] 3+ with excess NH3

A

No further change

35
Q

Explain why an aqueous solution containing
[Fe(H2O)6]3+ ions has a lower pH than
an aqueous solution containing [Fe(H2O)6]2+ ions.

A
  • Fe3+ is smaller (than Fe2+)
  • Fe3+ ions are more polarising
  • weaken O-H bonds in ligands more (in the Fe3+ solution) / more H+ released
36
Q

Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has
a pH ˂ 7

A

[Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)]2+ + H+
M2 Al3+ has a small size and high charge
M3 Weakens the OH bond (in water) releasing H+ ions