In each case, indicate which of these pairs of compounds is more likely to form ion pairs in water: (a) \(\mathrm{NaCl}\) or \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{MgCl}_{2}\) or \(\mathrm{MgSO}_{4},\) (c) \(\mathrm{LiBr}\) or \(\mathrm{KBr}\)

Understanding the solubility of ionic compounds is essential when predicting their behavior in solutions like water. Solubility refers to the ability of a substance to dissolve in a solvent, creating a homogeneous mixture. In the context of ionic compounds, which are made up of positively and negatively charged ions, their solubility in water depends on the attractive forces between the ions themselves and the water molecules.

Water, being a polar solvent, is very effective at disrupting the ionic lattice of a compound due to its own partial charges. Ions that can become surrounded by water molecules, a process known as hydration, will generally have higher solubility. In our exercise, NaCl and Na₂SO₄ both dissolve in water, but Na₂SO₄, having more ions, tends to show a greater degree of ion pairing due to the likelihood of its ions to find each other in solution.

When we look at the dissociation of salts, such as MgCl₂ and MgSO₄, we're referring to the process where solid ionic compounds dissolve in water and separate into their constituent ions. The strength of the ionic bond and the structure of the crystal lattice influences how readily a salt dissociates.

Dissociation Processes

For example, MgCl₂ splits into one magnesium ion and two chloride ions, resulting in three total ions. Conversely, MgSO₄ produces one magnesium ion and one sulfate ion, which still contributes to a higher number of overall particles in solution. This increase can lead to an increased likelihood of forming ion pairs, where the separate ions come back together momentarily in solution, especially at higher concentrations, even though the overall compound remains dissolved.

The concept of ionization energy is significant in understanding why certain ions form more readily in water. Ionization energy is the amount of energy required to remove an electron from an atom or ion in its gaseous state. It represents the strength of the electron's attachment to the atom.

As we compare LiBr to KBr, lithium has a higher ionization energy than potassium, which means that lithium holds onto its electrons more tightly and, when forming ions, it does so with more energy release. This energy release helps with the dispersal and hydration of ions in water, making LiBr more predisposed to forming ion pairs in aqueous solution due to its higher tendency to dissociate as compared to KBr.