Reactions of Ions in Aqueous solution

Question 1

Why can some metals dissolve?

Answer 1

becaue there is enough energy given out upon hydration to overcome the lattice enthalpy of the solid

Question 2

Why do metal (III) chlorides react more vigorously than any of the metal (II) salts with water?

Answer 2

because the metal (III) have a higher charge density (because they are 3+) so the enthalpy of hydration is much more exothermic

Question 3

What is the difference between a hydrolysis, substitution and redox reaction for metal- aqua cations?

Answer 3

• If the O-H bond within the water molecule is broken, then the reaction is called a hydrolysis reaction.
• If the Metal-O bond to the water ligand is broken, and a new ligand forms a bond with the metal ion, then the reaction is called a substitution reaction.
• ## A further reaction will be studied, in which neither bond is broken, but the metal changes oxidation state. This is a redox reaction.

Question 4

What are the two main factors which determines the acidity of a transition metal hexa-aqua ion?

Answer 4

• the size of the ion = the smaller the ion the higher the acidity
• the charge on the ion = the higher the charge the higher the acidity

Question 5

Why do small and highly charged ions show greater levels of acidity?

Answer 5

• small and highly charged cations are more polarising
• As a result, they attract the electron density away from the oxygen atoms in the water ligands → weakens O-H bond within molecule
• This makes it easier to break the O-H bond, so it is easier to release H+ ions to a water molecule which is not coordinated to the central metal ion

Question 6

What is the general equation for the equilibrium set up when metal aqua ions are placed in water?

Answer 6

Question 7

What happens when hexa-aqua iron (III) is added to water?

Answer 7

A hydrolysis reaction occurs

Question 8

What happens when metal-aqua ions react with alkali in a solution?

Answer 8

• The hydroxide ions react with the H3O+ ions present in the equilibrium which drives each hydrolysis equilibrium forward until the metal hydroxide is formed as a precipitate

Question 9

Describe the further hydrolysis of metal (III) ion. (the same process happens with metal (ii) ions)

Answer 9

Question 10

Why does further hydrolysis of metal ions only have two steps?

Answer 10

only two water ligands are needed to be deprotonated to form a neutral complex.

Question 11

How can hydrolysis of metal ions be reversed? Why is this possible?

Answer 11

• add a strong acid, forcing the equilibrium to the left
• the insoluble metal hydroxides accept the H+ ion due to being a Bronsted-Lowry base
• this is because they are amphoteric

Question 12

Write the hydrolysis equation and the reaction that reverses the hydrolysis for Aluminium hydroxide

Answer 12

b

Question 13

Why are metal 3+ aqua ions more acidic metal 2+ aqua ions?

Answer 13

+3 ions are smaller and therefore have a higher charge density than +2 ions

• The higher charge density pulls the water molecules more strongly, which weakens the O-H bond and results in more dissociation, producing a more acidic solution
• The metal ionpolarisesthe water molecules
• This results in hydrogen ions (protons) splitting from the complexes creating acidic solutions

Question 14

What happens when you add small amounts of NH3 to metal-aqua ions

Answer 14

adding small quantities of NH3 to a metal aqua ion produces the same metal hydroxides as adding a strong base, as this reaction produces OH- ions

Question 15

What happens when you add excess amounts of NH3 to metal-aqua ions (for some metal hydroxides)

Answer 15

• partial ligand substitution
• This forms a soluble charged complex = precipitate dissolves

Question 16

What happens when you add small amounts and excess amounts of NH3 to copper

Answer 16

Question 17

What happens when metal (II) ions react with sodium carbonate?

Answer 17

• complete substitution of the water ligands
• an insoluble metal carbonate is formed
• general equation:

Question 18

What happens when metal (III) ions react with sodium carbonate? Why does this happen?

Answer 18

• since metal (III) are stronger acids than metal (II) ions, there is a higher concentration of H3O+ ions in the solution
• This means instead of displacing water from the metal ions, the carbonate ions react with H3O+, removing them from the solution
• bubbles of co2 are formed
• this shifts the equilibria of the metal hexa ion solution to the right

Question 19

How do you identify the metal ion solutions with sodium hydroxide, ammonia and sodium carbonate?

Answer 19

Question 20

What does chelation mean?

Answer 20

The water molecules may be replaced by bi or multidentate ligands

Question 21

What happens when you react copper hexa-aqua ions with sodium cabronate solution?

Answer 21

Question 22

What happens when you react copper hexa-aqua ions with small amounts and excess amounts of OH-?

Answer 22

there is no change when excess OH is added (blue precipitate remains)

Question 23

What happens when you add small amounts and excess amounts of NH3 to iron (II)

Answer 23

No change for excess

Question 24

What happens when you react iron (II) hexa-aqua ions with sodium cabronate solution?

Answer 24

Question 25

What happens when you react iron (II) hexa-aqua ions with small amounts and excess amounts of sodium hydroxide solution?

Answer 25

No change in excess

Question 26

What happens when you add small amounts and excess amounts of NH3 to aluminium ions

Answer 26

Question 27

What happens when you react aluminium hexa-aqua ions with sodium cabronate solution?

Answer 27

Question 28

What happens when you react aluminium hexa-aqua ions with small amounts and excess amounts of sodium hydroxide solution?

Answer 28

aluminium hydroxide precipitate dissolves in excess of NaOH - ∵ it’s amphoteric - First equation: aluminium act as an acid by donating protons to the hydroxide ions to form 3 waters - Second equation: aluminium can also act as a base by accepting hydroxide ions to form the [Al(OH)6]3- complex ion (accepting hydroxide ions means its indirectly accepting protons = bronstead lowry base)

Question 29

What happens when you add small amounts and excess amounts of NH3 to iron (iii) ions

Answer 29

no change for excess

Question 30

What happens when you react iron (III) hexa-aqua ions with small amounts and excess amounts of sodium hydroxide solution?

Answer 30

Question 31

What happens when you react iron (III) hexa-aqua ions with sodium cabronate solution?

Answer 31