Question

Explain the reactions of water with metal with the help of example.

Answer 1

The reaction of water with metals: Metals react with water to form a metal oxide or metal hydroxide and hydrogen gas evolves. The reactivity of metals towards water depends upon the nature of the metals.

Some metals react even with cold water, some react with water only on heating while there are some metals that do not react even with steam. For example,

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

$\underset{\left(\mathrm{Pottasium}\right)}{2{\mathrm{K}}_{\left(\mathrm{s}\right)}}+\underset{(\mathrm{Cold}\mathrm{Water})}{2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}}\to \underset{(\mathrm{Pottasium}\mathrm{Hydroxide})}{2{\mathrm{KOH}}_{(\mathrm{aq}.)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}\uparrow }$
The reaction between sodium and water is so violent that the hydrogen evolved catches fire.

Calcium reacts with cold water to form calcium hydroxide and hydrogen gas. The reaction is less violent.

$\underset{\left(\mathrm{Calcium}\right)}{{\mathrm{Ca}}_{\left(\mathrm{s}\right)}}+\underset{(\mathrm{Cold}\mathrm{Water})}{2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}}\to \underset{(\mathrm{Calcium}\mathrm{Hydroxide})}{\mathrm{Ca}{{\left(\mathrm{OH}\right)}_2}_{(\mathrm{aq}.)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}\uparrow }$

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

$\underset{\left(\mathrm{Magnesium}\right)}{M{g}_{\left(\mathrm{s}\right)}}+\underset{(\mathrm{boil}\mathrm{Water})}{2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}}\to \underset{(\mathrm{Magnesium}\mathrm{Hydroxide})}{\mathrm{Mg}{{\left(\mathrm{OH}\right)}_2}_{(\mathrm{aq}.)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}\uparrow }$
Metals like zinc and aluminum react only with steam to form their respective oxides and hydrogen.

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

$\underset{\left(\mathrm{Aluminum}\right)}{2{\mathrm{Al}}_{\left(\mathrm{s}\right)}}+\underset{\left(\mathrm{steam}\right)}{3{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{g}\right)}}\to \underset{(\mathrm{Aluminum}\mathrm{oxide})}{{\mathrm{Al}}_2{{\mathrm{O}}_3}_{\left(\mathrm{s}\right)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{3{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}\uparrow }$

Iron metal does not react with water under ordinary conditions. The reaction occurs only when steam is passed over a red hot iron and the products are iron (II,III) oxide and hydrogen.

$\underset{(\mathrm{Red}\mathrm{hot}\mathrm{iron})}{{\mathrm{Fe}}_{\left(\mathrm{s}\right)}}+\underset{\left(\mathrm{steam}\right)}{2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{g}\right)}}\to \underset{(\mathrm{Iron}(\mathrm{ii},\mathrm{iii}\left)\mathrm{oxide}\right)}{{{\mathrm{Fe}}_2{\mathrm{O}}_3}_{\left(\mathrm{s}\right)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{{{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}\uparrow }$
Metals like copper, silver and gold do not react with water even under strong conditions.