Question

The order of solubility in water for sodium phosphate, sodium sulphate and sodium chloride is:

• A. sulphate > phosphate > chloride
• B. chloride > sulphate > phosphate
• C. chloride > phosphate > sulphate
• D. phosphate > chloride > sulphate

Answer 1

The correct option is B chloride > sulphate > phosphate

A compound is soluble in water if its lattice energy is less than hydration energy. Lattice energy depends on the product of the charges of the cation and the anion and inversely proportional to the internuclear distance between them.
Here, Charge on the anion increases as $C{l}^{-}<S{O}_4^{2-}<P{O}_4^{3-}$ and the size increases in the same order $C{l}^{-}<S{O}_4^{2-}<P{O}_4^{3-}$. As a result, the net lattice energy increases as follows: $NaCl<N{a}_{2}S{O}_4<N{a}_{3}P{O}_4$ as charge is dominating factor here.

Hence, the order of solubility is $NaCl>N{a}_{2}S{O}_4>N{a}_{3}P{O}_4$.