Question

The majority of ionic substances are solids at room temperature. Describe what you would observe if you placed a soluble ionic compound and an insoluble ionic compound in separate beakers of water.

Answer 1

Ionic compounds are formed when atoms of different charges (i.e. positive and negative ions) come together and form ionic bonds. These ionic bonds are typically very strong due to the high attractive forces holding the positively and negatively charged ions together (called electrostatic forces of attraction).

Because ionic compounds are formed by alternating positive and negative ions, and because they are all held together with these strong electrostatic forces, the oppositely charged ions pack tightly with each other and form a crystal lattice structure that is extremely hard to break. Thus, at normal room temperatures, the strength of these connections are much stronger than the kinetic energy of the ions, and so they cannot break away from each other! Instead, the ions are held rigidly together in their organized crystal lattice structure, and that is why they are a solid under normal conditions.

when a soluble ionic compound is placed in beaker , then the ionic compound dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process represents a physical change known as dissociation. example of this is common salt.

on the other hand when an insoluble ionic compound is placed in water,the electrostatic attractions between the ions are so large, or the ion-dipole attractive forces between the ions and water molecules are so weak, that the increase in disorder cannot compensate for the energy required to separate the ions, and the compound is insoluble. example for such a case is calcium carbonate (limestone), calcium phosphate (the inorganic component of bone), and iron oxide (rust).