REACTIONS WITH CHANGE OF VALENCY OXIDATION AND REDUCTION

REACTIONS WITH CHANGE OF VALENCY OXIDATION AND REDUCTION 

In the double decompositions just considered, the valencies of the reacting atoms remained unchanged. This is not always so, and a reaction can lead to the formation of an unstable compound which decomposes with a valency change to a lower value. If KI is added to CuCI2, the reaction is 

However, Cul2 is unstable and decomposes into Gul and iodine, the complete reaction therefore being 

If the reaction takes place in aqueous solution, then it can be written as an ionic one in which the K+, Cl- and some of the 1 ions remain unchanged, so that the ionic reaction is 

This electron transfer is even more general with highly-charged positive ions thus, if 0rO3, containing a hexavalent Cr ion, reacts with H2S, sulphur and a lower oxide of chromium are formed according to the equation 

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