Question

Which of the following is/are incorrect about the solubility trend in group I and II?
(a)The solubility of the alkali metal fluorides increases on moving down the group
(b)The solubility of alkali metal hydroxides decreases on moving down the group
(c)The solubility of hydroxides, fluorides and oxalates decreases from calcium to barium.
(d)The solubility of carbonates, sulphates and chromates decreases on moving down the group.

Answer 1

Hint: For some compounds solubility depends on the size of the cation moving down the group. Solubility for some compounds depends on hydration energy and lattice energy. This can cause variation in its trends.

Complete step by step answer:
Solubility of a compound is directly proportional to atomic size of the metals. So, in a group, the atomic size increases, so the solubility of the metal salt will increase moving down the group.
Let us consider all the options,
-In metal fluorides of group 1 and 2 , they have a common element fluorine, so the solubility depends on the size of the cation. On going down the group, the size of the cation increases and the salt becomes more ionic in nature. So, the solubility also increases down the group. Thus, the solubility of fluorides of alkali metals increases down the group. Option (a) is correct.
-Even alkali metal hydroxides, the cations of the group increases while going down the group. So, as size increases solubility increases. So, the solubility of alkali metal hydroxides increases down the group. Hence, the option (b) is incorrect.
-Elements from calcium to barium belong to group 2. The hydroxides, fluorides and oxalates of these elements solubility increases down the group. This is due to the decrease in lattice energy of the hydroxide salt(in case of hydroxides) and the size of the cation increases down the group. Hence, option (c) is incorrect.
-Sulphates of this group, their solubility decreases down the group. Also carbonates and chromates of group 2 become less soluble while moving down the group. This is due to the hydration energy decreasing as the cation size increases. So, the option (d) is correct.

Hence, the correct options are (a) and (d).

Note:
Alkaline metal carbonates are more stable than the alkaline earth metal carbonates. This is because of the hydration energy difference between the two groups. Hydration energy for group 2 metals is more than that of group 1 metals. This is because the size of alkaline earth metals is smaller and its increased charged ion when compared with alkaline metals.