redox reactions

Question 1

How can Fe3+ be reduced to Fe2+? Include the chemical equation and colour change

Answer 1

Reducing agent: Fe3+ ( pale green)
Oxidising agent Fe2+ ( yellow)
2Fe3+ + 2I- –> 2Fe2+ + I2
solution changes from yellow to pale green but appears brown because of I2

Question 2

What are the key redox reactions and color changes involving manganese, particularly with MnO4- and Mn2+?

Answer 2

• reduction of MnO4- = in acidic conditions MnO4- (purple) reduces to Mn2+ (pale pink)
  Mno4- + 8H+ +5e- –> Mn2+ + 4H2O

Question 3

How do you combine the half-equations for the oxidation of Fe2+ and the reduction of MnO4- in acidic conditions?

Answer 3

Fe2+ –> Fe3+ + e-
Mno4- + 8H+ +5e- –> Mn2+ + 4H2O
combined: 5Fe2+ + MnO4- + 8H+ –> 5Fe3+ + Mn2+ + 4H2O

Question 4

what is the balanced equation for the reduction of Cr2O7 2- using Fe2+ in acidic conditions? include colour changes

Answer 4

Cr2O7 2- +14H+ + 6Fe2+ –> 2Cr3+ + 7H2O + 6Fe3+
orange dichromate to green Cr3+

Question 5

how can Cr3+ be oxidised to chromate? include reagents and colour changes

Answer 5

• reagents = use hydrogen peroxide H2O2 in the presence of a base OH-
• Cr3+ green is oxidsed to Cro42- yellow
• 2Cr3+ + 10 OH- + 3H2O2 –> 8H2O + 2CrO4 2-

Question 6

What is the disproportionation reaction of copper(I) ions in aqueous solution, and what are the observations?

Answer 6

2Cu+ –> Cu2+ + Cu
solution turns blue and the solid copper is a ppt