Question

In the group analysis of cations, Ba$^{2+}$ & Ca$^{2+}$ are precipitated respectively as 
 

• A. hydroxide & carbonate
• B. sulphide & sulphide
• C. chromate & sulphide
• D. carbonate & carbonate

Hint:

Carbonate precipitation is a key step in identifying alkaline earth metal ions like Ba$^{2+}$ and Ca$^{2+}$ during qualitative inorganic analysis.

Answer 1

The Correct Option is D

The question asks about the precipitation of barium ions (Ba²⁺) and calcium ions (Ca²⁺) in the group analysis of cations. Their specific anionic partners will determine how they form precipitates.

Let’s analyze the reactions:

1. Ba²⁺ Precipitation: In the presence of carbonate ions (CO₃^2-), barium carbonate (BaCO₃) is formed as a white precipitate. \(\mathrm{Ba^{2+} + CO_3^{2-} \rightarrow BaCO_3 \, (precipitate)}\)
2. Ca²⁺ Precipitation: Similarly, calcium ions react with carbonate ions to form calcium carbonate (CaCO₃), which also precipitates as a white solid. \(\mathrm{Ca^{2+} + CO_3^{2-} \rightarrow CaCO_3 \, (precipitate)}\)

Thus, both Ba²⁺ and Ca²⁺ are precipitated as carbonates, leading to the conclusion that the respective precipitate for each cation is a carbonate.

Therefore, the correct answer is:

Carbonate & Carbonate

Justification of Other Options:

• Hydroxide & Carbonate: Barium and calcium both form carbonates as precipitates; hydroxides are not the typical precipitates in this scenario.
• Sulphide & Sulphide: Barium and calcium do not typically form sulphide precipitates in standard analysis.
• Chromate & Sulphide: Chromate is not applicable for Ca²⁺ precipitation, and sulphide is not the precipitate for Ca²⁺ either.

The focus in qualitative analysis is to correctly identify and differentiate ions based on their specific reactions and typical precipitates, which in this case are carbonates for both barium and calcium.