Question

The group reagent NH\(_4\)Cl (s) and aqueous NH\(_3\), will precipitate which of the following ion

• A. Al\(^{3+}\)
• B. Ba\(^{2+}\)
• C. Ca\(^{2+}\)
• D. NH\(_4^{+}\)

Hint:

To selectively precipitate ions in qualitative analysis, it's crucial to control the pH and the reagents used, as these factors determine which hydroxides will precipitate.

Answer 1

The Correct Option is A

When the group reagent NH\(_4\)Cl (ammonium chloride) and aqueous NH\(_3\) (ammonia) are added, a common ion effect is observed. The ammonia neutralizes the free H\(^+\) ions in the solution, creating a basic environment, and the NH\(_4\)Cl serves to provide ammonium ions (NH\(_4^{+}\)) that help precipitate metal hydroxides. This combination will precipitate the aluminum ion as aluminum hydroxide (Al(OH)\(_3\)). - For Al\(^{3+}\), ammonia creates a basic environment which results in the formation of Al(OH)\(_3\). - Ba\(^{2+}\) and Ca\(^{2+}\) would not precipitate under these conditions as their hydroxides are more soluble. - NH\(_4^{+}\) is already in its ionized form and will not precipitate. Thus, the correct answer is: \[ \text{(1) Al}^{3+} \text{ ppt as Al(OH)}_3 \text{ in presence of NH}_4\text{Cl and NH}_4\text{OH.} \]