Question

Which of the following options is the correct order for the basic strength of metallic hydroxides ?
(A) \[Ca{(OH)_2} < Al{(OH)_3} < Lu{(OH)_3} < Ce{(OH)_3}\]
(B) \[Al{(OH)_3} < Lu{(OH)_3} < Ce{(OH)_3} < Ca{(OH)_2}\]
(C) \[Lu{(OH)_3} < Ce{(OH)_3} < Al{(OH)_3} < Ca{(OH)_2}\]
(D) \[Lu{(OH)_3} < Ce{(OH)_3} < Ca{(OH)_2} < Al{(OH)_3}\]

Answer 1

Hint: The basicity of metal hydroxide increases as we move down the group. Group \[II\] metal hydroxides become more soluble in water as we move from left to right in a periodic table. The decrease in the lattice energy of the hydroxide salt and by the increase in the coordination number of the metal ion. And the covalent character of the hydroxides often increases and thus the basic strength decreases.

Complete Step by Step Solution:
The lanthanides, also known as lanthanons are a group of \[15\] elements of atomic numbers starting from \[57\] to \[71\] in which scandium (atomic number \[21\]) and yttrium (atomic number \[39\]) are sometimes included. Due to lanthanide contraction, the size of \[L{u^{3 + }},E{u^{3 + }},Y{b^{3 + }},C{e^{3 + }}\] decreases and thus, the basic strength of their hydroxides decreases.

Here all the given options containing hydroxides are from the group second also. These metals are called alkaline earth metal. As they go down in the group, the basic nature of hydroxide increases down in the group. The order of size is given \[Ce > Lu > Al\]. Generally the basic strength of hydroxides decreases as we move from left to right in a periodic table. So, alkali metal hydroxides are the most basic strength. The size of metal atoms increases, \[M - O\] bond length increases and the tendency to lose \[ - O{H^ - }\] group increases, that means basicity increases.

As we know, the order of basic strength of hydroxides from the least basic hydroxide to the most basic is \[Ca > Ce > Lu > Al\].
Thus, the order of basic strength is: \[Al{(OH)_3} < Lu{(OH)_3} < Ce{(OH)_3} < Ca{(OH)_2}\]
The correct option is: (B)\[Al{(OH)_3} < Lu{(OH)_3} < Ce{(OH)_3} < Ca{(OH)_2}\].

Note: Lanthanides are difficult to separate from each other because of similarities in their physical and chemical properties. Many of the separation processes take the advantage of a small decrease in the ionic radius that happens across the lanthanide series. The extracted liquid contains arms, called ligands, that grab the lanthanide. And calcium hydroxide and Aluminium hydroxide are Polyacid bases. calcium hydroxide \[(Ca{(OH)_2})\] has two ionizable \[O{H^ - }\] while aluminium hydroxide \[(Al{(OH)_3})\] has three ionizable.