Variable oxd states

Question 1

How do transition metal have variable oxd states?

Answer 1

• can use 3d electrons as well as 4s in bonding
• therefore it can have a greater variety of oxd states in compounds

Question 2

What does potassium manganate do?

Answer 2

• oxidising agent
• will oxidise Fe(II) to Fe(III)

Question 3

How is titration of Fe(II) carried out?

Answer 3

• used to measure conc of oxd or reducing agent
• Fe₂⁺ reacts with MnO₄^- (in potassium manganate(VII)) in ratio of 5:1
  
  • does not need indicator
• add potassium manganate(VII) soln to soln containing Fe²⁺ w/ excess dilute sulfurice acid
• purple colour disappears as the MnO₄^- ions are converted from purple to pale pink to leave a virtually colourless soln
• once enough MnO₄^- added, one more drop will turn the soln purple
  
  • this is the end pints

Question 4

Why can’t HCl be used instead of sulfuric acid in titration of iron?

Answer 4

• Cl^- oxideised by MnO₄^- ions

Question 5

What is the difference between the oxidation of TM metals w differnet oxd state?

Answer 5

• high oxd state
  
  • in acidic, e.g. Mn(VII) and Cr(VI)
• lower states happens in alkaline soln

Question 6

why does oxd of lower states happen in alkaline conditions?

Answer 6

• tendency to form -ve ions
• since oxd is electron loss, this is easier from -vely charged species that positively or neutral ones
• e.g. metal hydroxides

Question 7

What is the equation for the reaction of manganate ions with iron(II)?

Answer 7

5Fe²⁺ + MnO₄^- + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O