Transition Metals: Variable Oxidation States

Question 1

Colours of vanadium ions

Answer 1

+5- yellow
+4- blue
+3- green
+2- violet

Question 2

Manganate ions

Answer 2

MnO4,- strong reducing agent in acid, weak in base
Due to lowering of oxidation state

Question 3

Redox with potassium manganate

Answer 3

Colour change purple to pale pink
With iron, 1:5 ratio
With oxaloactetate, 2:5 ratio
For ironoxaloacetate 3:5 ratio

Question 4

Homogenous catalyst

Answer 4

Catalyst in same phase as reactants

Question 5

Heterogeneous catalyst

Answer 5

Catalyst in a different phase to reactants
Reactants adsorbed onto catalyst surface
Bonds in reactants are weakened
Reactants held in a more favourable configuration
Products desorbed from surface

Question 6

Catalyst poisoning

Answer 6

Heterogeneous catalyst
Poisoned by impurities
Coated to become passive and inactive

Question 7

Peroxodisulfate ions and iodide ions with Fe catalyst

Answer 7

2Fe2+ + S2O8,2- -> 2SO4,2- + 2Fe3+
2Fe3+ + 2I- -> I2 + 2Fe2+
Overall: S2O8,2- + 2I- -> I2 + 2SO4
Slow due to repulsion of like charges
Positive iron allows speedier reaction

Question 8

Autocatalysis of manganate with ethanedioate

Answer 8

5C2O4,2- + 2MnO4,- + 16H+ -> 10CO2 + 2Mn2+ + 8H2O
Initially slow as like charges repel
4Mn2+ + MnO4,- + 8H+ -> 5Mn3+ + 4H2O
2Mn3+ + C2O4,2- -> 2Mn2+ + 2CO2
Positive Mn2+ attracted to manganate increasing rate
Monitored using colorimeter