Question

In order for sodium chloride to dissolve in water, a small amount of energy must be added during solution formation. This is not energetically favorable. Why is NaCl so soluble in water?

Short answer

Sodium chloride (NaCl) is highly soluble in water due to the strong interaction between its ions (Na+ and Cl-) and the polar water molecules. When NaCl is added to water, the partial positive charges (hydrogen) of water molecules are attracted to the negative chloride ions, and the partial negative charges (oxygen) of water molecules are attracted to the positive sodium ions. This creates a strong hydration shell around the separated ions, compensating for the energy needed to overcome the lattice energy, making the dissolution process energetically favorable. Thus, the strong attraction between water molecules and NaCl ions results in the high solubility of NaCl in water.

Step-by-step solution

Understand the structure of Sodium Chloride (NaCl)

Sodium Chloride, commonly known as table salt, is an ionic compound with the chemical formula NaCl. It consists of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). In its solid state, the ions are arranged in a crystal lattice structure that maintains a strong electrostatic attraction between the ions.

Understand the process of solvation

Solvation is the process wherein solvent molecules surround and interact with solute particles, which in our case is water as the solvent and sodium chloride as the solute. For ionic compounds like NaCl, the solvent molecules (water) must overcome the strong electrostatic attraction between the ions in the crystal lattice. As the solvent molecules approach the ions, they form an electrostatic attraction with the ions and ultimately pull the ions away from the crystal lattice. This dissolving process is called dissociation.

Relate energy requirement to the dissolution process

The process of dissociation requires energy input, known as the lattice energy, to overcome the electrostatic attraction between the ions in the crystal lattice. However, energy is released when the water molecules attach to the separated ions, known as the hydration energy. In order for an ionic compound to dissolve, the energy released during hydration must be greater than or equal to the energy required to separate the ions (lattice energy).

Explain the reasons behind the high solubility of NaCl in water

Sodium chloride is highly soluble in water due to the strong interaction between its ions and the water molecules. Water is a polar molecule that can form hydrogen bonds; the oxygen atom has a partial negative charge, and the hydrogen atoms have partial positive charges. When NaCl is added to water, the positive ends (hydrogen) of water molecules are attracted to the negative chloride ions, while the negative ends (oxygen) of water molecules are attracted to the positive sodium ions. This creates a strong hydration shell around the separated ions, which compensates for the energy required to overcome the lattice energy, making the dissolution process energetically favorable. The strong attraction between water molecules and NaCl ions results in the high solubility of NaCl in water.