Which of the following is an example of a double replacement reaction?
A. 3Fe + 2O2 → Fe3O4
B. BaCl2 + K2CO3 → BaCO3 + 2KCl
C. NiCO3 → NiO + CO2
D. Cl2 + 2NaBr → 2NaCl + Br2
The Correct Answer and Explanation is :
The correct answer is B. BaCl2 + K2CO3 → BaCO3 + 2KCl, which is an example of a double replacement reaction.
Explanation:
A double replacement reaction (also known as a double displacement or metathesis reaction) occurs when parts of two compounds switch places to form two new compounds. The general form of this type of reaction is:
AB + CD → AD + CB
Here, the positive ion (cation) of one compound combines with the negative ion (anion) of another compound, and vice versa.
Breaking down the reaction:
- BaCl2 (Barium chloride) is composed of Ba²⁺ (barium ion) and Cl⁻ (chloride ions).
- K2CO3 (Potassium carbonate) is composed of K⁺ (potassium ions) and CO3²⁻ (carbonate ion).
In this reaction:
- The Ba²⁺ cation from BaCl2 pairs with the CO3²⁻ anion from K2CO3 to form BaCO3 (Barium carbonate).
- The K⁺ cations from K2CO3 pair with the Cl⁻ anions from BaCl2 to form 2KCl (Potassium chloride).
This swapping of ions is characteristic of a double replacement reaction.
Why Other Reactions Do Not Fit:
- Option A (3Fe + 2O2 → Fe3O4): This is a synthesis reaction, where iron (Fe) reacts with oxygen (O2) to form iron oxide (Fe3O4).
- Option C (NiCO3 → NiO + CO2): This is a decomposition reaction, where nickel carbonate (NiCO3) breaks down into nickel oxide (NiO) and carbon dioxide (CO2).
- Option D (Cl2 + 2NaBr → 2NaCl + Br2): This is a single replacement reaction, where chlorine (Cl2) replaces bromine (Br) in sodium bromide (NaBr) to form sodium chloride (NaCl) and bromine (Br2).
Thus, Option B clearly exemplifies a double replacement reaction, as two ionic compounds exchange ions to produce two new ionic compounds.