Question

Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute \[{{\text{H}}_{2}}S{{O}_{4}}.\]

Answer 1

Hint: We know that not all metals can displace hydrogen from an acid, when the metal reacts with acid. Only those metals which are above hydrogen in the activity series can undergo a single displacement reaction with an acid to give hydrogen gas.

Complete answer: As we know the chemical reaction, when one or more elements replace one or more elements in a compound, the reaction is called a single displacement reaction. When hydrochloric acid is added to iron fillings such a displacement occurs. Metals can displace hydrogen from an acid and form a salt and release hydrogen gas. It does not give salt and water like the reaction between acid and a base. Therefore, when dilute hydrochloric acid reacts with iron filling, the salt iron (II) chloride and hydrogen gas is produced. The single displacement reaction is represented as: $A+B-C\to A-C+B.$
Here A is more reactive than B, and C represents an anion or could be any halogen. In this reaction C is spectator ion, when AC and BC are aqueous compounds. Sometimes, displacement reactions can also act as redox reactions. Here are two types of such reaction, cation replacement reaction and anion replacement reaction. In cation replacement reactions, cation is replaced and is reduced whereas in anion replacement reaction an element in its reduced form is converted to its anion.
When dilute HCl react with reactive metal like alkali metal or alkali earth metal, Hydrogen gas is liberated example; \[Mg+2HCl\to MgC{{l}_{2}}+{{H}_{2}}\uparrow \]
Reaction when Iron reacts with dilute \[{{\text{H}}_{2}}S{{O}_{4}}\] ; ${{\overset{\left( 0 \right)}{\mathop{Fe}}\,}_{\left( s \right)}}+{{H}_{2}}S{{O}_{4\left( aq \right)}}\to \overset{\left( +2 \right)}{\mathop{Fe}}\,S{{O}_{4\left( aq \right)}}+{{H}_{2\left( g \right)}}$

Note:
Remember that the single displacement reaction is a chemical reaction in which one element replaces another element in a compound. Sometimes a single displacement reaction is also called a single replacement reaction. When an acid reacts with metals hydrogen gas is evolved in the form of bubbles and reaction is an exothermic reaction.