Question

The compound insoluble in acetic acid is
(A) Calcium oxide
(B) Calcium carbonate
(C) Calcium hydroxide
(D) Calcium oxalate

Answer 1

Hint: We know that the solubility of a substance in a given solvent depends on the solute-solute and solvent-solvent interactions existing between them. As the temperature is increased, the solubility also gets increased. Lattice energy is defined as the amount of energy required to break an ionic lattice into its constituent ions.

Complete answer:
-We know that the solubility of salt depends on the lattice energy of the solid and hydration energy of the ions.
-From the definition of lattice energy we can conclude that the higher the lattice energy, the higher will be energy required to break the bonds between the ions in an ionic lattice and the higher the lattice energy, the lower will be the solubility.
-Here acetic acid is a polar solvent and it has a strong hydrogen bonding attraction force between them.
-For alkaline earth metal salts, solubility depends on the hydration energy of the ions and the lattice energy of the solid.
-So for the first option, calcium oxalate is insoluble in acetic acid due to its high lattice energy and low hydration energy.
-Calcium oxide is soluble in acetic acid as its hydration energy is more than its lattice energy.
-Calcium carbonate and calcium hydroxide are soluble in acetic acid as its hydration energy is greater than lattice energy.
-So the compound insoluble in acetic acid is calcium oxalate and the other three are soluble.
-Since acetic acid is an acid, it undergoes a chemical reaction with oxides, carbonates, and hydroxides and no reaction with oxalates.
So the correct answer is option D.

Note:The oxalic salts have not been decomposed by acetic acid as it is a stronger acid than acetic acid. Also, the solubilities of alkaline earth metal salts are dependent on hydration energy.