One Element by Another Activity Series

Displacing One Element by Another Activity Series As we said, displacement reactions have the same number of reactants as products. We mentioned doubledisplacement (metathesis) reactions in discussing precipitation and acid-base reactions. The other type, single-displacement reactions, are all oxidation-reduction processes. They occur when one atom displaces the ion of a different atom from solution. When the reaction involves metals, the atom reduces the ion when it involves nonmetals (specifically halogens), the atom oxidizes the ion. Chemists rank various elements into activity series—one for metals and one for halogens— in order of their ability to displace one another. 

The activity series of the metals. Metals can be ranked by their ability to displace H2 (actually reduce H ) from various sources or by their ability to displace one another from solution. 

Still less reactive metals, such as nickel and tin, do not react with water but do react with acids. Because the concentration of is higher in acid solutions than in water, H2 is displaced more easily. Here is the net ionic equation  

Notice that in all such reactions, the metal is the reducing agent (O.N. of metal increases), and water or acid is the oxidizing agent (O.N. of H decreases). The least reactive metals, such as silver and gold, cannot displace H2 from any source. 

A metal displaces another metal ion from solution. Direct comparisons of metal reactivity are clearest in these reactions. For example, zinc metal displaces copper(II) ion from (actually reduces Cu in) copper(II) sulfate solution, as the total ionic equation shows  

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