Question

Which of the following is least soluble?
A.\[Be{F_2}\]
B.\[Sr{F_2}\]
C.\[Ca{F_2}\]
D.\[Mg{F_2}\]

Answer 1

Hint: We must know the maximum amount of substance which is soluble in a definite amount of solvent at a specific temperature. Mainly two factors will affect the solubility and that is, temperature and pressure. The temperature will affect the solubility of both gases as well as solid. The solubility will increase with increase in temperature. But in the case of pressure, it will affect only the solubility of gases. Polarity, molecular size and stirring also affect the solubility.

Complete answer:
The beryllium fluoride is not having least solubility. Hence, option (A) is incorrect.
Among the following compounds, the strontium fluoride has the least solubility. Because, the hydration energy will affect the solubility of the compounds. The hydration energy is equal to the liberated energy when any compound is soluble in water. If the hydration energy is higher than lattice energy, then the compound will soluble. Here, the hydration energy decreases when moving down the group. Then the solubility also decreases when moving down the group. Therefore, strontium fluoride has the least solubility. Hence, option (B) is correct.
The calcium fluoride is not having least solubility. Hence, option (C) is incorrect.
The magnesium is not having least solubility. Hence, option (D) is incorrect.

Hence, option (B) is correct.

Note:
The hydration energy will affect the solubility. The solubility decreases with decrease in solubility. Therefore, we can say that the hydration energy is directly proportional to the solubility. But the lattice energy is inversely proportional to the hydration energy. And both hydration energy and lattice energy decrease down the group.