Investigation of the oxidation states of vanadium

Chemicals :

0.1 M FeSO4 , 0.1 M Fe2(SO4)3 ,

0.1 M KI , 0.1 M KBr ,

0.1 M I2 in KI , aqueous SO2 ,

copper powder , zinc powder ,

1 M H2SO4

Procedure:

how did you make you solutions of V(II) , V(III) and V(IV) for the experiment

How did you make you solutions of V(II) , V(III) and V(IV) for the experiment?

Standard Electrode Potential

Zn2+ + 2 e− = Zn(s) −0.76

Fe2+ + 2 e− = Fe(s) −0.44

V3+ + e− = V2+ −0.26

SO42− + 4 H+ + 2 e− = SO2(aq) + 2 H2O +0.17

Cu2+ + 2 e− = Cu(s) +0.34

VO2+ + 2 H+ + e− = V3+ + H2O +0.34

I2(s) + 2 e− = 2 I− +0.54

Fe3+ + e− = Fe2+ +0.77

VO2 ++2H++e- =H2O + VO2+ +1.00

Br2(aq) + 2 e−= 2 Br− +1.07

2VO2^+(aq) + SO2(aq) → 2VO^2+(aq) + SO4^2-(aq)

according to　Standard Electrode Potential

VO^2+ will be reduced to V3+

### 1 個解答

• 1 十年前
最愛解答

Preparation of V(V) solution in a strongly acidic medium:

Place one spatula measure of solid ammonium vanadate(V), NH4VO3, in a beaker and added about 25 mL of 1 M sulphuric acid and about 5 mL of concentrated sulphuric acid. Stir until a yellow solution is obtained. This yellow solution is V(V) solution which contains dioxovanadium(V) ions.

VO3^-(aq) + 2H^+(aq) = VO2^+(aq) + H2O(l) .. (reversible)

Preparation of V(II) solution :

To a half of the V(V) solution obtained above, add zinc power, a little at a time with stirring. Heat if necessary. When the solution has become violet, filter the mixture. The violet solution obtained is the V(II) solution which contains vanadium(II) ions.

2VO2^+(aq) + 3Zn(s) + 8H^+(aq) → 2V^2+(aq) + 3Zn^2+(aq) + 4H2O(l)

Preparation of V(IV) solution :

To some of V(V) solution obtained above in a test tube, add equal volume of aqueous SO2 and shake. Then boil the solution carefully in a fume cupboard in order to remove excess sulphur dioxide. The blue solution obtained is the V(IV) solution which contains oxovanadium(IV) ions.

2VO2^+(aq) + SO2(aq) → 2VO^2+(aq) + SO4^2-(aq)

or 2VO2^+(aq) + SO3^2-(aq) + 2H^+ → 2VO^2+(aq) + SO4^2-(aq) + H2O(l)

Preparation of V(III) solution:

Mix equal volumes of V(IV) solution and V(II) solution both obtained above. The green solution obtained is the V(III) solution which contains vanadium(III) ions.

VO^2+(aq) + V^2+(aq) + 2H^+(aq) → 2V^3+(aq) + H2O(l)

2010-01-05 23:12:43 補充：

I've never used aqueous SO2 in laboratory, and it is not commercially available.

2010-01-05 23:14:06 補充：

In my experience, V(IV) solution is made by adding a spatula measure of Na2SO3 to V(V) solution, filtering if necessary, and then boiling the solution to remove excess SO2. This is a method of preparing V(IV) solution recommended by ILPAC (Independent Learning Project for Advanced Chemistry).

2010-01-05 23:27:29 補充：

V(IV) solution can also be made by reducing V(V) solution with KI(aq).

2VO^2+(aq) + 2I^-(aq) + 4H^+ → 2V^3+(aq) + I2(aq) + 2H2O(l)

The brown I2(aq) can be removed by added Na2S2O3(aq).

2S2O3^2-(aq) + I2(aq) → S4O6^2-(aq) + 2I^-(aq)

However, it is mixed with a reducing agent, I^- ions.

• 登入以回覆解答