Reactions of inorganic compounds in aqueous solutions - Chapter 24

Question 1

Why are solutions of Fe3+ more acidic than solutions of Fe2+?

Answer 1

Fe3+ is both a smaller ion and more positively charged
Makes it more strongly polarising
So when forming an aqua ion the Fe3+ more strongly attracts the electrons from the oxygens on the water ligands
This weakens the O-H bond in the water ligands, and breaks some of them
This causes the H+ ion to be released, making the water more acidic
Because Fe2+ is less polarising fewer O-H bonds will break in solution

Question 2

Fe3+ aqua ion reaction with water equation

Name the type of reaction

Answer 2

[Fe (H20)6] 3+ (aq) + H20 (l) ⇌ [Fe (H20)5 (OH)] 2+ (aq) + H30+ (aq)
Hydrolysis

Question 3

M (H20)3 (OH)3 properties

Answer 3

Neutral (uncharged)

Insoluble (forms a precipitate)

Question 4

M2+ aqa ion plus ammonia equation

Answer 4

[M (H20)6] 2+ (aq) + 2NH3 (aq) —-> M (H20)4 (OH)2] (s) + 2NH4+

Question 5

Carbonates of transition metal ions rule

Answer 5

In general, carbonates of transition metal ions exist in oxidation states of 2+ but not in states of 3+.

Question 6

What is the carbonate ion?

Answer 6

CO3 2-

Question 7

Reaction of Fe3+ aqua ion with carbonate ions

Answer 7

2[Fe (H20)6] 3+ (aq) + 3CO3 2- (aq) —-> 2[Fe (H2O)3 (OH)3] (aq) + 3CO2 (g) + 3H20 (l)

Question 8

What can you add to Fe3+ and Fe2+ aqua ions to better distinguish between them, and how does this work?

Answer 8

Add a dilute alkali (OH-)
The colours of the iron aqua ions are more difficult to tell apart when they are in their aqueous forms. Adding OH- causes them to form a coloured precipitate, and these have more distinct looking colours.

Question 9

What can replace water as a ligand, and is replacement of water ligands complete or partial?

Answer 9

• Other neutral ligands, such as ammonia
• Negatively charged ligands, such as Cl- ions
• Replaced by multidentate ligands such as [EDTA] 4- (Chelation)
• Replacement of water ligands can be either complete or partial

Question 10

When water is replaced by other neutral ligands, what change is seen in the co-ordination number?

Answer 10

None

Question 11

Adding concentrated ammonia to [Co (H20)4 (OH)2] (s)
Write the equation and explain why this reaction occurs in the way it does
Give the colour changes

Answer 11

[Co (H20)4 (OH)2] (s) + 6NH3 (aq) ⇌ [Co (NH3)6] 2+ (aq) + 4H20 (l) + 2OH- (aq)

1. Because ammonia is a better ligand than water
2. The high ammonia concentration displaces equilibria, which displaces water and OH-

Blue precipitate to pale yellow solution

Question 12

[X (H20)4 (OH)2] is called ion Y
When ion Y reacts with ammonia the water and hydroxide ion ligands are completely replaced by the ammonia
Give examples of what X could be

Answer 12

Magnesium

Cobalt

Question 13

How many ethylene diamine ligands replace 6 water ligands? And what kind of ligand is ethylene diamine?

Answer 13

Three

Bidentate ligand

Question 14

How many [EDTA]4- molecules replace six water ligands?

Answer 14

One

Question 15

What is a chelate?

Answer 15

A complex with a polydentate ligand

Question 16

Why are the formation of chelates favoured?

Answer 16

Because a large number of entities on the right side of the reaction means that there is a large entropy increase from the left side of the reaction to the right.

Question 17

[Fe (H2O)6] 2+ colour and colours after adding bases

Answer 17

[Fe (H2O)6] 2+ = Pale green

OH- little Green gelatinous ppt of [Fe (H20)4 (OH)2]
OH- excess Green gelatinous ppt of [Fe (H20)4 (OH)2]
NH3 little Green gelatinous ppt of [Fe (H20)4 (OH)2]
NH3 excess Green gelatinous ppt of [Fe (H20)4 (OH)2]
CO3 2- Green ppt of FeCO3

Question 18

[Cu (H2O)6] 2+ colour and colours after adding bases

Answer 18

[Cu (H2O)6] 2+ = Pale blue

OH- little Pale blue ppt of [Cu (H20)4 (OH)2]
OH- excess Pale blue ppt of [Cu (H20)4 (OH)2]
NH3 little Pale blue ppt of [Cu (H20)4 (OH)2]
NH3 excess Pale blue ppt of [Cu (NH3]4 (OH)2]
CO3 2- Blue-green ppt of CuCO3

Question 19

[Fe (H2O)6] 3+ colour and colours after adding bases

Answer 19

[Fe (H2O)6] 3+ = yellow

OH- little Brown gelatinous ppt of [Fe (H20)3 (OH)3]
OH- excess Brown gelatinous ppt of [Fe (H20)3 (OH)3]
NH3 little Brown gelatinous ppt of [Fe (H20)3 (OH)3]
NH3 excess Brown gelatinous ppt of [Fe (H20)3 (OH)3]
CO3 2- Brown gelatinous ppt of [Fe (H20)3 (OH)3] and bubbles of CO2

Question 20

[Al (H2O)6] 3+ colour and colours after adding bases

Answer 20

[Al (H2O)6] 3+ = Colourless

OH- little White ppt of [Al (H2O)3 (OH)3]
OH- excess Colourless solution of [Al (OH)4]-
NH3 little White ppt of [Al (H2O)3 (OH)3]
NHS excess White ppt of [Al (H2O)3 (OH)3]
CO3 2- White ppt of [Al (H2O)3 (OH)3] and bubbles of CO2

Question 21

What shows the greater acidity of [M (H20)6] 3+ in comparison to [M (H20)6] 2+

Answer 21

When carbonate ions are added to M2+ ions, precipitates of the metal carbonate forms. When carbonate ions are added to M3+ ions, CO2 is produced instead.