Question

Write the chemical equation representing the reaction of zinc with the following
dilute sulphuric acid.

Answer 1

Hint: The metals which are on the top of the activity series are more reactive than the metals
which are at the bottom. If any metal which is situated above hydrogen in the activity series
reacts with dilute acid, it forms a salt of the acid and liberates hydrogen. This is not possible for
the metals below hydrogen in the series. Find out if zinc in below or above hydrogen in the series
and write the reaction accordingly.

Complete step by step answer:
When a metal reacts with dilute acid it liberates hydrogen gas. This is only possible if the metal
is above hydrogen in the activity series. But let us first know more about the activity series.
The activity series is a series of metal and hydrogens which are placed from top to bottom with
decreasing reactivity. That is the topmost metal will be the most reactive. The activity series is
given below:

K Potassium
Na Sodium
Ca Calcium
Mg Magnesium
Al Aluminium
Fe Iron
Pb Lead
H Hydrogen
Cu Copper
Hg Mercury
Ag Silver
Au Gold

As we can see from this series that zinc is above hydrogen in this series. So it will react with
dilute acids to liberate hydrogen. These kinds of reactions are known as displacement reactions. In
these reactions, the metal reacts with dilute acid and displaces the hydrogen and bonds with the
anion present in the acid.
Thus, zinc will react with dilute sulphuric acid to form zinc sulphate and hydrogen gas. The
a balanced chemical reaction is given below.
\[\underset{\text{Zinc}}{\mathop{\text{Z}{{\text{n}}_{\left( \text{s}
\right)}}}}\,+\underset{\text{Sulphuric
Acid}}{\mathop{{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}_{\left(
\text{dil}\text{.} \right)}}}\,\to \underset{\text{Zinc
Sulphate}}{\mathop{\text{ZnS}{{\text{O}}_{\text{4}}}_{\left( \text{aq}
\right)}}}\,+\underset{\text{Hydrogen Gas}}{\mathop{{{\text{H}}_{2}}_{\left( g
\right)}\uparrow }}\,\]
Therefore, we can say that Zinc displaced hydrogen from the dilute sulphuric acid and hence zinc is more reactive than hydrogen.

Note: Remember that zinc only on reaction with dilute sulphuric acid produces hydrogen gas.
When zinc reacts with concentrated sulphuric acid it produces sulphur dioxide gas along with
zinc sulphate and water. This is because concentrated sulphuric acid is a strong oxidizing agent
and the hydrogen gas produced is oxidized into water and sulphuric acid itself gets reduced into
sulphur dioxide. This is an example of a redox reaction.
\[\underset{\text{Zinc}}{\mathop{\text{Z}{{\text{n}}_{\left( \text{s}
\right)}}}}\,+\underset{\text{Sulphuric
Acid}}{\mathop{\text{2}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}_{\left(
\text{conc}\text{.} \right)}}}\,\to \underset{\text{Zinc
Sulphate}}{\mathop{\text{ZnS}{{\text{O}}_{\text{4}}}_{\left( \text{aq}
\right)}}}\,+\underset{\text{Water}}{\mathop{\text{2}{{\text{H}}_{2}}{{O}_{\left( l
\right)}}}}\,+\underset{\text{Sulphur dioxide}}{\mathop{S{{O}_{2}}_{\left( g
\right)}\uparrow }}\,\]