Reactions of Ions in Aqueous solution Flashcards
Why can some metals dissolve?
becaue there is enough energy given out upon hydration to overcome the lattice enthalpy of the solid
Why do metal (III) chlorides react more vigorously than any of the metal (II) salts with water?
because the metal (III) have a higher charge density (because they are 3+) so the enthalpy of hydration is much more exothermic
What is the difference between a hydrolysis, substitution and redox reaction for metal- aqua cations?
- 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.
What are the two main factors which determines the acidity of a transition metal hexa-aqua ion?
- 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
Why do small and highly charged ions show greater levels of acidity?
- 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
What is the general equation for the equilibrium set up when metal aqua ions are placed in water?
What happens when hexa-aqua iron (III) is added to water?
A hydrolysis reaction occurs
What happens when metal-aqua ions react with alkali in a solution?
- 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
Describe the further hydrolysis of metal (III) ion. (the same process happens with metal (ii) ions)
Why does further hydrolysis of metal ions only have two steps?
only two water ligands are needed to be deprotonated to form a neutral complex.
How can hydrolysis of metal ions be reversed? Why is this possible?
- 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
Write the hydrolysis equation and the reaction that reverses the hydrolysis for Aluminium hydroxide
b
Why are metal 3+ aqua ions more acidic metal 2+ aqua ions?
+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
What happens when you add small amounts of NH3 to metal-aqua ions
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
What happens when you add excess amounts of NH3 to metal-aqua ions (for some metal hydroxides)
- partial ligand substitution
- This forms a soluble charged complex = precipitate dissolves
What happens when you add small amounts and excess amounts of NH3 to copper
What happens when metal (II) ions react with sodium carbonate?
- complete substitution of the water ligands
- an insoluble metal carbonate is formed
- general equation:
What happens when metal (III) ions react with sodium carbonate? Why does this happen?
- 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
How do you identify the metal ion solutions with sodium hydroxide, ammonia and sodium carbonate?
What does chelation mean?
The water molecules may be replaced by bi or multidentate ligands
What happens when you react copper hexa-aqua ions with sodium cabronate solution?
What happens when you react copper hexa-aqua ions with small amounts and excess amounts of OH-?
there is no change when excess OH is added (blue precipitate remains)
What happens when you add small amounts and excess amounts of NH3 to iron (II)
No change for excess
What happens when you react iron (II) hexa-aqua ions with sodium cabronate solution?
What happens when you react iron (II) hexa-aqua ions with small amounts and excess amounts of sodium hydroxide solution?
No change in excess
What happens when you add small amounts and excess amounts of NH3 to aluminium ions
What happens when you react aluminium hexa-aqua ions with sodium cabronate solution?
What happens when you react aluminium hexa-aqua ions with small amounts and excess amounts of sodium hydroxide solution?
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)
What happens when you add small amounts and excess amounts of NH3 to iron (iii) ions
no change for excess
What happens when you react iron (III) hexa-aqua ions with small amounts and excess amounts of sodium hydroxide solution?
What happens when you react iron (III) hexa-aqua ions with sodium cabronate solution?
