Question

La(OH)3 is more basic than Lu(OH)3 because
La has high ionisation enthalpy than Lu
La3+ is larger in size than Lu3+
lonic character of bond in Lu(OH)3 is high
O All of these

Answer 1

Explanation:

Due to lanthanide contraction, the size of Lu3+ is decreased and therefore Lu(OH)3 shows more covalent character (Small cation, more is covalent character - Fajan's rule). Thus La(OH)3 is more ionic and thus more basic.

Answer 2

$\[La{(OH)_3}\]$ is more basic than $\[Lu{(OH)_3}\]$ because $\[L{a^{3 + }}\]$ is larger in size than $\[L{u^{3 + }}\]$.

Explanation:

• The size of lanthanides decreases from $\[L{a^{3 + }}\]$ to $\[L{u^{3 + }}\]$ due to lanthanide contraction.
• With the decrease in size of the lanthanides, the covalent character of the hydroxides of lanthanides increases.
• More the covalent character of the hydroxide, less basic is the hydroxide.
• It means basicity decreases from $\[L{a^{3 + }}\]$ to $\[L{u^{3 + }}\]$.
• Therefore, $\[Lu{(OH)_3}\]$ has less ionic character than $\[La{(OH)_3}\]$.
• Hence, $\[La{(OH)_3}\]$ is more basic than $\[Lu{(OH)_3}\]$ due to larger size of $\[L{a^{3 + }}\]$ than $\[L{u^{3 + }}\]$.