Question

Why is \( La(OH)_3 \) a stronger base than \( Lu(OH)_3 \)?

Hint:

Lanthanoid contraction reduces atomic size across the series, affecting basicity trends.

Answer 1

Step 1: Basicity and Lanthanoid Contraction: - As we move across the lanthanide series, atomic size decreases due to lanthanoid contraction.
- \( La(OH)_3 \) has a larger ionic radius, making it more basic than \( Lu(OH)_3 \). 

Step 2: Explanation: - Larger ionic size in \( La^{3+} \) leads to weaker bond strength in \( La(OH)_3 \), making hydroxide ions (\( OH^- \)) more available.
- \( Lu^{3+} \) has a smaller radius, leading to a stronger attraction between \( Lu^{3+} \) and \( OH^- \), reducing basicity.