24 - Reactions of Inorganic Compounds in Aqueous Solutions

Question 1

How are hexaaqua ions formed?

Answer 1

If a salt of a transition metal is dissolved in water the aqueous metal ions attract the water molecules and six water molecules surround it. The water acts as a Lewis base and forms a coordinate bond to the metal ion which accepts the lone pair.

Question 2

What is a Lewis base?

Answer 2

Lone pair donor

Question 3

What is a Lewis acid?

Answer 3

Lone pair acceptor.

Question 4

Are transition metals acidic or alkaline in water?

Answer 4

Acidic

Question 5

Why are transition metals acidic in water?

Answer 5

The transition metal ion pulls the electron density from the oxygen towards itself (polarising it), so it is easier for another water molecule from the solution to remove a H+ from a water ligand to form H3O+.

Question 6

Why are some transition metals in water more acidic than others?

Answer 6

Transition metals with a greater charge are more polarising, so it is easier for a water molecule to remove a H+ so the solution becomes more acidic.

Question 7

Is water a weak or strong base and how many protons can it remove during hydrolysis?

Answer 7

Weak
1 proton

Question 8

Are NH3 and CO3 2- a weak or strong base sand how many protons can they remove during hydrolysis?

Answer 8

Medium strength
Removes protons until precipitation

Question 9

Is OH- a weak or strong base and how many protons can it remove during hydrolysis?

Answer 9

Strong
Can remove all protons.

Question 10

When does precipitation occur during hydrolysis of a transition metal ion?

Answer 10

When sufficient electrons have been removed the complex ion becomes neutral and a precipitate of a hydroxide or carbonate forms.

Question 11

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

Answer 11

Light blue

Question 12

What is the formula for the reaction between [Cu(H2O)6]2+ and a little OH-?

Answer 12

[Cu(H2O)6]2+(aq) + 2OH-(aq) –> [Cu(H2O)4(OH)2] (s) + 2H2O(l)

Question 13

What is the formula for the reaction between [Cu(H2O)6]2+ and excess OH-?

Answer 13

[Cu(H2O)4(OH)2] (s) is insoluble in excess NaOH.

Question 14

What is the formula for the reaction between [Cu(H2O)6]2+ and a little NH3?

Answer 14

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

Question 15

What is the formula for the reaction between [Cu(H2O)6]2+ and a CO3 2-?

Answer 15

[Cu(H2O)6]2+(aq) + CO3 2-(aq) –> CuCO3(s) + 6H2O(l)

Question 16

What colour is [Cu(H2O)4(OH)2] (s)?

Answer 16

Blue

Question 17

What colour is CuCO3(s)?

Answer 17

Blue-green

Question 18

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

Answer 18

Pale green

Question 19

What is the formula for the reaction between [Fe(H2O)6]2+ and a little OH-?

Answer 19

[Fe(H2O)6]2+(aq) + 2OH-(aq) –> [Fe(H2O)4(OH)2] (s) + 2H2O(l)

Question 20

What colour is [Fe(H2O)4(OH)2] (s) when it is first formed?

Answer 20

Dirty green

Question 21

What colour is [Fe(H2O)4(OH)2] (s) in air?

Answer 21

Rusty brown, as it is oxidised by the air to Fe(III).

Question 22

What is the formula for the reaction between [Fe(H2O)6]2+ and excess OH-?

Answer 22

Insoluble in excess NaOH.

Question 23

What is the formula for the reaction between [Fe(H2O)6]2+ and a little NH3?

Answer 23

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

Question 24

What is the formula for the reaction between [Fe(H2O)6]2+ and excess NH3?

Answer 24

Insoluble in excess NH3.

Question 25

What is the formula for the reaction between [Fe(H2O)6]2+ and CO3 2-?

Answer 25

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

Question 26

What colour is FeCO3(s)?

Answer 26

Off-white

Question 27

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

Answer 27

Pale yellow

Question 28

What is the formula for the reaction between [Fe(H2O)6]3+ and a little OH-?

Answer 28

[Fe(H2O)6]3+(aq) + 3OH-(aq) --> [Fe(H2O)3(OH)3] (s) + 3H2O(l)

Question 29

What is the formula for the reaction between [Fe(H2O)6]3+ and excess OH-?

Answer 29

Insoluble in excess OH-.

Question 30

What colour is [Fe(H2O)3(OH)3] (s)?

Answer 30

Rusty brown

Question 31

What is the formula for the reaction between [Fe(H2O)6]3+ and a little NH3?

Answer 31

[Fe(H2O)6]3+(aq) + 3NH3(aq) --> [Fe(H2O)3(OH)3] (s) + 3NH4+(l)

Question 32

What is the formula for the reaction between [Fe(H2O)6]3+ and excess NH3?

Answer 32

Insoluble in excess NH3.

Question 33

What is the formula for the reaction between [Fe(H2O)6]3+ and CO3 2-?

Answer 33

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

Question 34

Why does Fe(III) not form a carbonate when reacting with CO3 2-?

Answer 34

The high charge density of the Fe3+ makes the solution too acidic to form a carbonate.

Question 35

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

Answer 35

Colourless

Question 36

Why can aluminium form hexaaqua complex ions?

Answer 36

Although aluminium isn't a transition metal as it doesn't use the d-orbital its high charge density means the Al3+ ions behave as 3+ transition metals.

Question 37

What does amphoteric nature mean?

Answer 37

The substance can act as both an acid and base.

Question 38

What metal ions are amphoteric?

Answer 38

Metal ions of 3+ charge have a high charge density, so their hydroxides can dissolve in both acid and alkali.

Question 39

What is the formula for the reaction between [Al(H2O)6]3+ and a little OH-?

Answer 39

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

Question 40

What is the formula for the reaction between [Al(H2O)6]3+ and excess OH-?

Answer 40

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

Question 41

What colour is [Al(H2O)3(OH)3] (s)?

Answer 41

White

Question 42

What is the formula for the reaction between [Al(H2O)6]3+ and a little NH3?

Answer 42

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

Question 43

What is the formula for the reaction between [Al(H2O)6]3+ and excess NH3?

Answer 43

Insoluble in excess NH3

Question 44

What is the formula for the reaction between [Al(H2O)3(OH)3] and H+?

Answer 44

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

Question 45

What is the formula for the reaction between [Al(H2O)3(OH)3] and OH-?

Answer 45

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

Question 46

When can ligand substitution occur?

Answer 46

If other ligand form stronger co-ordination bonds (better Lewis Bases) If other ligands are present in higher concentration, so equilibrium is displaced.

Question 47

What determines if partial of complete ligand substitution occurs?

Answer 47

Gibbs free energy Entropy

Question 48

What are the possible ligands that could substitute water ligands?

Answer 48

Neutral ligands (e.g. NH3) Negatively charged ligands (e.g. Cl-) Bi or multidentate ligands (chelation)

Question 49

Why is NH3 a better ligand than water?

Answer 49

The nitrogen is less electronegative than the oxygen, so the lone pair of electrons are held less strongly so they are more readily donated (better Lewis base).

Question 50

What effect does ligand substitution of NH3 have on the complex ion?

Answer 50

Co-ordination number stays the same, as both H2O and NH3 are neutral and similar in size.

Question 51

What is the formula for the reaction of [Co(H2O)4(OH)2] and excess NH3?

Answer 51

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

Question 52

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

Answer 52

Pink

Question 53

What is the colour of [Co(NH3)6]2+(aq)?

Answer 53

Yellow

Question 54

What is the colour of [Co(H2O)4(OH)2] (s)?

Answer 54

Blue

Question 55

What is the formula for the reaction of [Cu(H2O)4(OH)2] and excess NH3?

Answer 55

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

Question 56

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

Answer 56

Distorted octahedron - the four NH3 molecules exist in a square planar arrangement with the H2O molecules above and below. Its distorted as Cu-O bonds are longer than Cu-N.

Question 57

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

Answer 57

Deep royal blue.

Question 58

How does ligand substitution of Cl- ions affect the complex ion?

Answer 58

As chloride ions are larger than water molecules fewer ligands can fit around the transition metal ion so there is a decrease in co-ordination number.

Question 59

What is the formula for the reaction between [Cu(H2O)6]2+ and Cl-?

Answer 59

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

Question 60

What is required for ligand substitution with chlorine?

Answer 60

A high concentration of chloride ions.

Question 61

What is the colour of [CuCl4]2-(aq)?

Answer 61

Yellow

Question 62

What is the shape of [CuCl4]2-(aq)?

Answer 62

Tetrahedral

Question 63

What is chelation?

Answer 63

The substitution of unidentate ligands with bi or multidentate ligands to form more stable complexes.

Question 64

Why are chelation reactions more favourable?

Answer 64

There will be more species on the right, leading to a big increase in entropy, this increases Gibbs free energy, favouring the formation of chelates.

Question 65

What is a chelate?

Answer 65

A polydentate ligand bonded to a transition metal.

Question 66

What is chelation used for?

Answer 66

To remove heavy metals from the blood.