Question

Explain the following:
(a) Double decomposition reaction
(b) Neutralization reaction

Hint:

Double decomposition involves ion exchange between two salts, while neutralization involves acid-base reaction forming salt and water.

Answer 1

(a) Double Decomposition Reaction:
Step 1: Definition.
A double decomposition reaction is a type of chemical reaction in which two compounds exchange their ions or radicals to form two new compounds. It generally occurs in aqueous solutions.
Step 2: General equation.
\[ AB + CD \rightarrow AD + CB \] Here, the positive and negative ions of the two reactants interchange their partners.
Step 3: Example.
\[ \text{Na}_2\text{SO}_4 + \text{BaCl}_2 \rightarrow 2\text{NaCl} + \text{BaSO}_4 \downarrow \] Observation: A white precipitate of barium sulphate (BaSO4) is formed.
Step 4: Conclusion.
This reaction shows ion exchange between reactants, producing a precipitate — hence it is a double decomposition (precipitation) reaction.
(b) Neutralization Reaction:
Step 1: Definition.
A neutralization reaction is the reaction between an acid and a base to form salt and water. The reaction neutralizes both the acid and the base.
Step 2: General equation.
\[ \text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water} \] Step 3: Example.
\[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \] Observation: The solution becomes neutral (pH = 7) after reaction.
Step 4: Conclusion.
In a neutralization reaction, hydronium ions (H+) from acid combine with hydroxide ions (OH–) from base to form water, leading to neutralization.