COMMON REDOX REACTIONS

5.2 SOME COMMON REDOX REACTIONS

Reaction of (left to right)lithium with water, calciumwith water, zinc withsulfuric acid, magnesiumwith hydrochloric acid

These reactions are called displacement reactions. Common reactive metals,Mg, Al, Zn, Fe, will displace both copper and silver from solutions of theirions and copper will displace silver. The more reactive metals, sodium, lithium,calcium and barium, cannot be used in such displacement reactions becausethey would react with the water of the aqueous solution (part (b) above).

Two displacementreactions: (a) a granuleof zinc dropped into acopper sulfate solution;(b) copper wire dippedinto a silver nitratesolution. For each casethe left-hand test tubeshows the metal just afterbeing dropped into thesolution: in the right-handtest tube the metal hasbeen in the solution forten to twenty minutes

In these reactions the negative bromide and iodide ions lose electrons to formthe neutral bromine and iodine molecules; hence the bromide and iodide areoxidised. The neutral molecules, chlorine and bromine, gain electrons (that is,get reduced) to form the negative chloride and bromide ions.The reverses of these reactions are not possible: bromine cannot oxidisechloride; iodine cannot oxidise chloride or bromide.Fluorine has been omitted from this discussion because it is so reactive thatit oxidises water to oxygen and thus cannot be used in the type of aqueoushalogen–halide reactions described here.