Question

The solubility in water of sulphates down the Be group is $Be > Mg > Ca > Sr > Ba$. This is due to
A. High heat of solvation for smaller ions like $B{e^{2 + }}$
B. Increasing molecular weight
C. Decreasing lattice energy
D. Increase in melting points

Answer 1

Hint: The elements Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra) belong to group 2 of the periodic table. Out of the group 2 elements radium is radioactive (half-life $ = $1590 years). These elements are called alkaline earth metals since their oxides are alkaline like alkali metal oxides and the oxides of calcium, strontium, and barium are found on earth’s surface.

Complete step by step answer:
The solubility of an ionic compound depends upon two factors: Lattice energy and Hydration energy.
Lattice energy as well as hydration energy values decrease with an increase in the size of ions and increases with an increase in charge of ions.
The solubility of the sulphates of alkaline earth metals decreases down the group. For example $BeS{O_4}$ and $MgS{O_4}$ are highly soluble in water but $BaS{O_4}$ is insoluble in water. This is because the size of the cation (metal ion) being much smaller than the size of the anion$\left( {SO_4^{2 - }} \right)$, the lattice energy remains practically constant and the solubility of the salt is mainly dependent on hydration energy. It is because the hydration energy decreases down the group, the solubility of sulphates is also decreased down the group.
So we can say that the solubility in water of sulphates down the Be group $Be > Mg > Ca > Sr > Ba$ is due to the high heat solvation for smaller ions like $B{e^{2 + }}$.

So, the correct answer is Option A.

Note: All the alkaline earth metals have two electrons in their outermost shell, s-orbital i.e. all these elements have $n{s^2}$ configuration.
Since all the alkaline earth metals possess identical $n{s^2}$ configuration these elements resemble closely in their physical and chemical properties.
Alkaline earth metals do not occur in a free state because of their highly reactive nature.
Beryllium is an unfamiliar metal because it does not occur in abundance and is difficult to extract. Magnesium and Calcium occur in definite amounts in the earth’s crust. Strontium and Barium are familiar elements and are easy to extract but do not occur in concentrated ores.
Since Radium is radioactive, it is very rarely found.