Chemistry

Vanadium its Chemical Properties Explained



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This articles discusses the chemical properties of Vanadium, V only; the physical properties of this element can be found easily in any standard Chemistry textbook.

Vanadium, atomic number 23, is a typical transition metal (the transition metals are best represented by elements from Sc through Zn). Because of the fact that their 3d and 4s level electrons exist in similar energy states, transition metals exhibit variable oxidation states as the atoms lose electrons forming cations (positively charged ions) of approximately the same stability.

As all chemistry students are aware, the chemical properties of an element is primarily the function of the electronic configuration of its atom - in this case, Vanadium, V has the following electronic structure: [ Ar ] 3d34s2. And, as noted above, Vanadium loses 2 to a possible 5 electrons of its sub-shells, resulting in the fact that Vanadium forms compounds in which its oxidation states are +2, +3, +4 and +5.

However, if V forms compounds with its highest oxidation of +5, this will result in ions of high charge density and therefore compounds in which V exhibits +5 oxidation state are usually covalently bonded as in V2O5 or contain complex ions ( what are commonly known as the 'transition metal complexes' ) as in VO3 - .

The chemical properties of Vanadium are a reflection of the variable oxidation states of this element and the best way to illustrate this is by carrying out an experiment which will show vividly the various chemical compounds formed with Vanadium exhibiting its 4 possible oxidation states.

EXPERIMENT TO SHOW THE VARIOUS OXIDATION STATES OF Vanadium, V

Aim and object: to demonstrate that V can exist in all its oxidation states, +2 through +5

Chemicals required: a compound of Vanadium, viz ammonium vanadate (V) and zinc granules, Zn, plus molar solutions of NaOH, sodium hydroxide, and molar solution of sulphuric acid, H2SO4.

Method and procedure:

1. About 2-3 g of ammonium vanadate, NH4VO3, are dissolved in 80 cm3 (cm cubed) of molar solution of NaOH and then 100 cm3 of molar solution of sulphuric acid is added thereto and shaken well. The resulting aqueous solution is yellow in colour, displaying the colour of VO2+ in which Vanadium exhibits +5 oxidation state:

VO3- (aq) + 2 H+ (aq) VO2+ (aq) + H2O (l)

2. The resulting yellow solution is then shaken with granulated zinc and the changes in colour are to be observed carefully. You would notice that the yellow colour changes progressively through green to blue, and finally the solution assumes a violet colour. This is explained by the fact that the original yellow VO2+ ion changes to green V 3+ ion, in which Vanadium takes on the oxidation state of +3, and then to blue VO2+ ions showing the oxidation state of +4 and it then reverts to green V3+ ions again before finally turning to a violet colour, exhibiting vanadium (II) ions or oxidation state of +2.

OTHER IMPORTANT CHEMICAL PROPERTIES OF VANADIUM, V

Although Vanadium is among the transition elements, it does not, like most of its counter-parts in this grouping of elements, readily form many complex ions as in the case of elements like Titanium, Ti, or Chromium, Cr, which form many colourful complexes with ligands like Cl- ions and H2O molecules.

One of the most important chemical properties of Vanadium is the use of its compounds, specifically V2O5 or Vanadium (V) oxide, as a catalyst in the important Contact Process in the manufacture of sulphuric acid and other related products.

In the Contact Process, sulphur dioxide is oxidized to sulphur (VI) oxide with the help of the catalyst V2O5:

SO2 + 1/2 O2 SO3, with V2O5 as catalyst, which speeds up the process by reducing the activation energy required for the conversion.

I do not propose here to elaborate on the actual chemistry involved; we just need to know that in catalyzing the conversion, V2O5 converts initially SO2 to SO3 while it itself is reduced from V (5+) to V (4+) and thence it is re-oxidized from the +4 state to + 5 state in the second stage of the catalysis process.

Vanadium is a precious transition element which is useful industrially as well as playing an important role in other chemical reactions in both organic and inorganic chemistry, a direct consequence of its variable oxidation state arising from the electronic structure of its atom.

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