Question

The correct trend of acidity of the ions is

• A. \( [Fe(H_2O)_6]^{2+} \)>\( [Fe(H_2O)_6]^{3+} \)>\( [Al(H_2O)_6]^{3+} \)
• B. \( [Al(H_2O)_6]^{3+} \)>\( [Fe(H_2O)_6]^{3+} \)>\( [Fe(H_2O)_6]^{2+} \)
• C. \( [Fe(H_2O)_6]^{2+} \)>\( [Al(H_2O)_6]^{3+} \)>\( [Fe(H_2O)_6]^{3+} \)
• D. \( [Fe(H_2O)_6]^{3+} \)>\( [Fe(H_2O)_6]^{2+} \)>\( [Al(H_2O)_6]^{3+} \)

Hint:

Higher charge and smaller ionic radius increase the polarization of water molecules, leading to higher acidity of the ion.

Answer 1

The Correct Option is B

Step 1: Acidity and ionization.
The acidity of the ions is directly related to the charge on the metal ion and its size. A higher charge and smaller size lead to greater polarization of the water molecules, making the ion more acidic.
Step 2: Understanding each ion's acidity.
- \( [Al(H_2O)_6]^{3+} \): Aluminum has a higher charge and smaller size compared to iron, making it the most acidic.
- \( [Fe(H_2O)_6]^{3+} \): Iron with a +3 charge is highly acidic, but slightly less than \( [Al(H_2O)_6]^{3+} \).
- \( [Fe(H_2O)_6]^{2+} \): Iron with a +2 charge is less acidic because the smaller charge leads to lower polarization.
Step 3: Conclusion.
The trend in acidity is \( [Al(H_2O)_6]^{3+} \)>\( [Fe(H_2O)_6]^{3+} \)>\( [Fe(H_2O)_6]^{2+} \).
Final Answer: \[ \boxed{[Al(H_2O)_6]^{3+}>[Fe(H_2O)_6]^{3+}>[Fe(H_2O)_6]^{2+}} \]