Reactivity Series

Reactivity series is the series of metals based on their reactivity from highest to lowest. So, the reactivity series of metals can be defined as a series of metals, in order of reactivity from highest to lowest. It is also known as activity series. The reactivity of metals is because of their incomplete outer orbitals or due to their electronic configuration. Metals form positively charged ions as they tend to lose electrons. Metals with high atomic numbers tend to be more reactive as their electrons are far from the positively charged nucleus, so, they can be removed easily. 

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Long Tabular Form of the Reactivity Series 

Metals from potassium to calcium are highly reactive and even react with water. While metals from magnesium to lead can react with acids. Metals from copper to platinum are highly unreactive and don’t react with any other substance in normal conditions. This is the reason why platinum and gold don’t get corrode easily and don’t form oxides. While metals such as zinc, aluminium, magnesium, calcium, etc. form oxides readily. Hydrogen is a non-metal but still, it has been included in the reactivity series as it helps in the comparison of reactivity of metals.

The reactivity of the metals is given below in another tabular format where it has been mentioned along with its ions. Here metals are segregated in terms of their reaction with cold water, hot water, acid, and steam and reaction with concentrated mineral acids. Here is the tabular format of the same.

Salient Features of reactivity series

• Metals present at the top of the reactivity series are highly electropositive metals. The electropositive character of metals decreases as we go down the series. 

• The reducing power of metals decreases as we go down the series. Thus, potassium is the strongest reducing agent. 

• As we go down the reactivity series, the ability of metals to remove hydrogen from hydrides decreases. 

• Metals present in the reactivity series above hydrogen can remove hydrogen ions from dilute HCl or Dilute sulphuric acid. 

• The metal which is more reactive than other metals can remove less reactive metal from its salt. Thus, metals placed at the top of the reactivity series can remove the metals which are present at the bottom of the series from their salts. 

• The metals which are placed above in the series can be extracted by electrolysis. While metals from Zinc to Hg can be extracted by simply reducing their oxides, which is an inexpensive method.  

• When we move down the series the electron-donating capacity of metals decreases.

Important Uses of Reactivity Series 

• In displacement reaction – Displacement reactions are those reactions in which more reactive metal displaces less reactive metal from its salt. So, by reactivity series, you can tell which metal will displace another metal. 

• The reaction between metals and water – Metals from potassium to calcium can react with cold water and release hydrogen gas. 

Chemical Equations for the reaction of K and Ca with cold water are:

Reaction 1:   

K (s) + H₂O (l) → KOH (aq) + ½ H₂ (g)

Potassium Cold Water Potassium Hydroxide Hydrogen

Note: Potassium reacts extremely violently with water to form a colourless aqueous solution of KOH with a release of12mole of H2 gas. The resultant solution is basic because of the dissolved hydroxide.

Reaction 2:

Ca + H₂O (l) → Ca(OH)₂ (aq) + ½ H₂ (g)

Calcium Cold Water Calcium Hydroxide Hydrogen 

Note: Ca virtually remains unreactive with cold water; however, it forms calcium hydroxide with a release of half a mole of H₂ gas.

• The reaction between metals and acids – Lead and other metals which are more reactive than lead in the reactivity series can react with hydrochloric acid and sulphuric acid and form salts. Thus, we can predict the reactions by reactivity series. Chemical Equations for the reaction of Pb with HCl and HSO₄ to form salts are: 

Reaction 1:   

 Pb (s) + 2HCl (aq) → PbCl₂ (aq) + H₂ (g)

Lead Hydrochloric Acid Lead Chloride Hydrogen

Note: Pb reacts slowly with acids like HCl and HNO₃ and releases bubbles of Hydrogen gas on reaction.

Reaction 2:   

Pb (s) + 2 H₂SO₄ → PbSO₄ + SO₂ + H₂O

Lead Sulphuric acid lead Sulphate (II) Sulphur Dioxide Water  

Note: Lead does not react with sulphuric acid, that’s why the reaction takes place in the boiling solution. Lead on reacting with 2 moles of HSO4, forms lead sulphate (II), sulphur dioxide with the release of water.

Single displacement reaction between metals: The high-ranking metals on the reactivity series readily reduce the ions of the low-ranking metals. Thus the high-ranking metal easily displaces the low-ranking metal in a single displacement reaction that occurs between them. One of the most common displacement reactions is the displacement of copper from copper sulphate by zinc the chemical equation for this reaction is given by:

Zn (s) + CuSO_{4 (}aq) → ZnSO₄(aq) + Cu (s)

This concept is used in various applications mostly for the extraction of metals. For example, with the help of the single displacement reaction with magnesium titanium can be extracted from titanium tetrachloride. Thus to predict the outcome of the single displacement reaction, the reactivity series becomes very useful.

Short Trick to Remember Reactivity Series

“Please send charlie’s monkeys and zebras in lead & hydrogen cages in mountains securely guarded by Plato.” 

In the above-given sentence, first alphabet of every word denotes the elements of the reactivity series in order of their reactivity from highest to lowest. You can understand this better by the table given below.