vanadium and its variable oxidation states

learn how to complete and combine redox reactions and then don't bother learning the eqns !! but they're here for completion's sake

how many oxidation states does vanadium exist in? give the oxidation state, formulae and colour of the species:

4 oxidation states:

• +5: VO₂⁺ - yellow

• +4: VO²⁺ - blue

• +3: V³⁺ - green

• +2: V²⁺ - violet

give the eqn for the conversion of VO₂⁺ → VO²⁺ - is this oxidation or reduction?

oxidation: 2H⁺ + e^- + VO₂⁺ → VO²⁺ + H₂O

give the eqn for the conversion of VO²⁺ to V³⁺ - is this oxidation or reduction?

oxidation: VO²⁺ + 2H⁺ + e^- → V³⁺ + H₂O

give the eqn for the conversion of V³⁺ to V²⁺ - is this oxidation or reduction?

V³⁺ + e^- → V²⁺

how are the V species in different oxidation states formed? what is the role of this substance? give the half eqn:

• add Zn metal in acidic solution

• acts as the reducing agent

• Zn → Zn²⁺ + e^-

give the eqn for the conversion of VO₂⁺ to VO²⁺ using Zn:

2VO₂⁺ + Zn + 4H⁺ → 2VO²⁺ + Zn²⁺ + 2H₂O

give the eqn for the conversion of VO²⁺ to V³⁺ using Zn:

2VO²⁺ + Zn + 4H⁺→ 2V³⁺ + Zn²⁺ + 2H₂O

give the eqn for the conversion of V³⁺ to V²⁺ using Zn:

2V³⁺ + Zn → 2V²⁺ + Zn²⁺

what is Tollens’ reagent for?

to distinguish between aldehydes and ketones

what oxidation state is silver usually found in? give the ½ eqn for its reduction:

• +1 oxidation state

• Ag⁺ + e^- → Ag

what is the complex ion present in Tollens’ reagent? describe the process that occurs when an aldehyde is added:

• [Ag(NH₃)₂]⁺

• when an aldehyde is added - oxidised to a carboxylate anion - RCOO^- - and Ag⁺ ions reduced to Ag metal