Question

Many ionic compounds dissolve in water, but not all. For example, NaCl is very soluble in water, but CaO is only alrighty soluble. Explain in terms of both internal and external forces

Answer 1

answer : CaO form Ca(OH)₂ with water which is insoluble in water or very less soluble

reaction : CaO + H₂O Ca(OH)₂

both NaCl and CaO are ionic solid and

Ionic solid solubility depends following factors

(i) the ability to break the bonds of the solid and

(ii) the stability of the ions in solution.

In CaO ,Ca is in +2 and O is in -2 oxidation state respectively, attraction between them is extremely strong

whereas in case of NaCl , Na is in +1 and Cl is in -1 oxidation state respectively

CaO enthalpy of formation is −635 kJ·mol^-1

enthalpy of formation is -411.12 kJmol^-1 for NaCl

so it is extremely hard to separate the two ions of CaO compare to NaCl

In dissolving most salts, a cation and an anion are separated in solution. For CaO, the anion is O₂^-

O₂^- is an extremely reactive species. It will quickly react with water take its hydrogen to form two OH^-

The more acidic the water, the more protons, and this is why CaO dissolves in acids. The acid also reduces the concentration of hydroxide ions that are available to react with calcium to form Ca(OH)_2..