Question

Correct order for solubility of alkaline earth metal fluorides in water is:

• A. \(MgF_2>CaF_2>SrF_2>BaF_2\)
• B. \(MgF_2<CaF_2<SrF_2<BaF_2\)
• C. \(MgF_2 BaF_2\)
• D. \(BaF_2>MgF_2>SrF_2>CaF_2\)

Hint:

Alkaline earth fluorides: Solubility decreases down the group (MgF\(_2\) > BaF\(_2\)).

Answer 1

The Correct Option is A

The question asks for the correct order of solubility of alkaline earth metal fluorides in water. The compounds in question are magnesium fluoride (\(MgF_2\)), calcium fluoride (\(CaF_2\)), strontium fluoride (\(SrF_2\)), and barium fluoride (\(BaF_2\)).

The solubility behavior of alkaline earth metal fluorides in water generally decreases as we move down the group in the periodic table. This property is influenced by the lattice energy and the hydration energy of the compounds.

1. Lattice Energy: It is the energy required to separate one mole of an ionic solid into gaseous ions. It increases with the charge on the ions and decreases with the size of the ions. In fluoride compounds, the lattice energy decreases down the group as the size of cations increases. This makes lighter cations (like Mg²⁺) form stronger and less soluble compounds.
2. Hydration Energy: It is the energy released when gaseous ions dissolve in water. It also decreases down the group as the radius of the ions increases.

The interplay between decreasing lattice energy and hydration energy results in the solubility trend. In the case of alkaline earth metal fluorides, the effect of decreasing lattice energy is more pronounced in terms of affecting solubility trends. As a result, solubility decreases as we move down the group from magnesium to barium:

• \(MgF_2\) is the most soluble.
• \(CaF_2\) follows.
• \(SrF_2\) is less soluble than calcium fluoride.
• \(BaF_2\) is the least soluble.

Thus, the correct order for solubility of alkaline earth metal fluorides in water is:

\(MgF_2 > CaF_2 > SrF_2 > BaF_2\)

Conclusion: The correct answer is \(MgF_2 > CaF_2 > SrF_2 > BaF_2\).