AIM To make samples of the less common oxidation states of vanadium with different colours

by zulhilmiazmi7777 (student)

Mohamad Zulhilmi bin Azmi

930813-05-5385

Chemistry HL

INTRODUCTION

Vanadium's ground state electron configuration is [Ar] 3d34s2. When transition elements ionize, they lose their valence s electrons before losing their d electrons. Vanadium has 5 valence electrons that one of the characteristics of transition metal is their ability to adopt multiple oxidation states. Vanadium exhibits four common oxidation states +5, +4, +3, and +2 each of which can be distinguished by its colour.

AIM

To make samples of the less common oxidation states of vanadium with different colours

HYPOTHESIS

Different oxidation states of vanadium show distinct colours. One of the special characteristics of transition elements is its ability to form coloured complexes like vanadium. This is because it has variable oxidation numbers. The colours formed are predominantly due to the splitting of the d shell orbitals into slightly different energy levels. As a result, certain wavelengths of energy can be absorbed by the d-block elements (with electrons jumping between these slightly different energy levels), resulting in the complement color being visible.

VARIABLE

APPARATUS AND MATERIALS

PROCEDURE

A spatula of measured ammonium metavanadate(V) was placed in a conical flask and then followed by 25 ml of dilute sulphuric acid. 5 ml of concentrated sulphuric acid was added into the conical flask. The flask was then swirled until a clear yellow solution was formed.
2 ml of this vanadium (V) solution was poured into two test tubes ready for later tests
A spatula of zinc powder was added into the conical flask a little each time. The flask was then swirled with intervals. The data was recorded.
2 ml of the product was filtered ...

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PROCEDURE

A spatula of measured ammonium metavanadate(V) was placed in a conical flask and then followed by 25 ml of dilute sulphuric acid. 5 ml of concentrated sulphuric acid was added into the conical flask. The flask was then swirled until a clear yellow solution was formed.
2 ml of this vanadium (V) solution was poured into two test tubes ready for later tests
A spatula of zinc powder was added into the conical flask a little each time. The flask was then swirled with intervals. The data was recorded.
2 ml of the product was filtered into two test tubes after the solution has turned violet
An excess acidified potassium manganete was added a little each time into one of the test tube in step 4 and then shake until no further change was observed.
A little sodium sulphite was added into one of the test tube from step 2 and filtered. The product was then boiled to remove excess sulphur dioxide and then was added by the same volume of vanadium(II) solution. The result was recorded.
2 ml of potassium iodide was added into other test tube from step 2. After that, potassium thiosulphate was added. The result was recorded.

SAFETY MEASURES

Concentrated sulphuric acid solution is corrosive and reacts violently with water. Below action is compulsory:

wear safety goggles and gloves;
when diluting, add acid to water, not water to acid;
mop up small spillages with excess water.

TABULATION OF DATA

Raw data:

Processed data :

CONCLUSION

All of the oxidation states of vanadium showed distinct coloured complexes. V+5 shows yellow colour, V+4 shows blue, V+3 shows green while V+2 shows violet. Vanadium is one of the transition elements which have variable oxidation numbers. This is because 4s and 3d sub shells are close in energy, and there are no big jumps in the successive ionisation energies when the 4s and 3d electrons are removed; therefore the number of electrons lost will depend on a variety of factors, such as lattice enthalpy. Due to this fact, each complexes formed by this different oxidation states show different colours. The colours formed are predominantly due to the splitting of the d shell orbitals into slightly different energy levels. As a result, certain wavelengths of energy can be absorbed by the d-block elements (with electrons jumping between these slightly different energy levels), resulting in the complement color being visible. So, hypothesis is accepted.

At the beginning of the experiment, Ammonium metavanadate(V) was mixed with dilute and concentrated sulphuric acid to reduced VO3- ion and became hydrated V2+. The yellow colour can only be observed with the presence of this year. Despite that, both ions have the same oxidation state that is +5.

The process of reduction from oxidation state +5 to +2 was done by the addition of zinc metal. The oxidation states of vanadium subsequently reduced from +5 to +4 followed by +3 and finally +2. The changes in colour explain the reduction process. However, the yellow colour turn green first instead of blue. Actually, the green colour is not the new oxidation state that is +3. It is just a mixture of the original yellow and the blue that is being produced.

Acidified potassium manganete (VII) is an oxidising agent which oxidise vanadium(II) to become vanadium(III). The colour change from violet to green explained the increment of oxidation number of vanadium from +2 to +3.

EVALUATION

A weakness was discovered throughout the experiment regarding the procedure. Firstly, all the apparatus containing vanadium solution was not closed using cotton wool. There is always a possibility for the vanadium solution especially with oxidation states below than +5 to be oxidised by oxygen in the air. To solve this problem, every apparatus containing any oxidation states of vanadium should be close with cotton wool. By using this method, we can avoid or reduce the possibility of re-oxidation of the oxidation states which may affect the colour formed.

All in all, this experiment has succeeded to show different colour of distinct oxidation states of vanadium which is one of the special characteristics of transition elements.

REFERENCES

[1] n.a. (n.d.) Retrieved from: