Question

Give the reason why metals are arranged in a series called “activity series of metal”. Name a metal that reacts with cold water, boiling water, and steam to liberate hydrogen in each case.

Answer 1

“ACTIVITY SERIES OF METALS”
On the basis of the reactivity of different metals with oxygen, water, and acids as well as displacement reactions, the metals have been arranged in the decreasing order of their reactivities.
The arrangement of metals in order of decreasing reactivities is called the “activity series of metals”.

Characteristics of reactivity series:

• The metal which is higher in the activity series is more reactive than the others. Lithium is the most reactive and platinum is the least reactive metal.
• The metals which have been placed above hydrogen are more reactive than hydrogen and these can displace hydrogen from its compounds like water and acids to liberate hydrogen gas.
• The metals which are placed below hydrogen are less reactive than hydrogen and these cannot displace hydrogen from its compounds like water and acids.
• A more reactive metal (placed higher in the activity series) can displace the less reactive metal from its salt solution.
• Metals at the top of the series are very reactive and, therefore, do not occur free in nature. The metals at the bottom of the series are least reactive and, therefore, they normally occur free in nature. For example, gold, present in the reactivity series is found in the free state of nature.

Part 1: Metal reacts with cold water

• Sodium and potassium metals react vigorously with cold water to form their respective hydroxides and hydrogen gas is liberated.
  $\underset{\left(\mathrm{Sodium}\right)}{2\mathrm{Na}\left(\mathrm{s}\right)}+\underset{(\mathrm{Cold}\mathrm{Water})}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{Sodium}\mathrm{Hydroxide})}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{\mathrm{H}}_2\left(\mathrm{g}\right)\uparrow }$

Part 2: Metal reacts with hot water

• Magnesium does not react with cold water but reacts rapidly with hot boiling water forming magnesium oxide and hydrogen.

$\underset{\left(\mathrm{Magnesium}\right)}{\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{(\mathrm{boil}\mathrm{Water})}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{Magnesium}\mathrm{Hydroxide})}{\mathrm{Mg}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{\mathrm{H}}_2\left(\mathrm{g}\right)\uparrow }$

Part 3: Metal reacts with cold steam

• Metals like zinc and aluminum react only with steam to form their respective oxides and hydrogen.

$\underset{\left(\mathrm{Zinc}\right)}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Steam}\right)}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{Zinc}\mathrm{oxide})}{\mathrm{ZnO}}+\underset{\left(\mathrm{Hydrogen}\right)}{{\mathrm{H}}_2\uparrow }$