Final answer:
Certain sodium salts exhibit low solubility due to factors like stable crystalline structures, which require more energy to break apart than is provided by hydration. Additional factors such as the common ion effect, solution pH, and complex ion formation also influence the solubility of these salts.
Step-by-step explanation:
Almost all salts with sodium as a cation are indeed water-soluble due to their ability to be dissociated into ions in a watery solution. However, there are exceptions to this solubility rule. For example, certain sodium salts such as sodium bismuthate and sodium fluorosilicate show low solubility.
The insolubility of these specific salts may be due to several factors including the ionic character of the salt, the lattice energy of the salt crystal, and the hydration energy of the ions.
When salts dissolve, they dissociate into their constituent ions which are then surrounded and stabilized by water molecules in a process called hydration. Some ions, like those in sodium bismuthate or sodium fluorosilicate, form very stable crystalline structures that require a large amount of energy to break apart; this energy may not be sufficiently offset by the hydration energy provided by water molecules.
Other factors influencing solubility include the common ion effect, pH of the solution, and the presence of complex ions or compounds that can form between the constituents of the dissolved substance and ions in water. These factors can sometimes create circumstances where even salts with typically soluble cations like sodium become less soluble.