Acid-base chemsitry of aqueous transition metals

Question 1

What are aqua ions?

Answer 1

• dissolve a salt of a transition metal in water
• water cluster around the transition metal ion
• exists as aqua ion in an octahedral arrangement

Question 2

How is charge distributed in a aqua ion?

Answer 2

• electrons pair in coordinate bond between metal ion and the oxygen are pulled towards the +ve metal ion
• that cause the electron pairs in the O-H bonds to be pulled closer to the oxygen than normal
• that makes the hydrogen atoms even more +ve than they normally are when attached to oxygen
  
  • nucleus more exposed

Question 3

How do hexaaqua ions act as acids?

Answer 3

• complex ion releases H+ as the O-H bond is more likely to break as it is weakend

Question 4

Why is Fe²⁺ less acidic than Fe³⁺

Answer 4

• Fe3+ has a higher charge density
  
  • smaller and more highly charged
• more strongly polarising
• this weakens of the O-H bond smaller
  *

Question 5

Why are the reactions hydrolysis reaction?

Answer 5

• react with water to form H₃O⁺
• This pulls off the H+
  
  • can also be written as H+ as a product (simplified version)
• water acts as a base

Question 6

How is a neutral complex formed?

Answer 6

• further loss of hydrogen results in a neutral complex
  
  • no charge
• doesn’t dissolve in water to any extent, and a precipitate is formed

[M(H₂O)₆]³⁺ (aq) + 3H₂O (l) ⇌ [M(H₂O)₃(OH)₃] (s) + 3H₃O⁺ (aq)

Question 7

Why does pH depend on conc?

Answer 7

• Le chatelier principle
• shift equilibrium to right if there is a high conc of the hexaqua ion