Question

This chapter opens with a discussion of ocean acidification. a. Seawater contains many salts, including sodium chloride. Write its chemical formula. b. Sodium chloride is soluble in water. What chemical process takes place when solid sodium chloride dissolves?

Short answer

a) NaCl; b) Dissociation into Na^+ and Cl^- ions in water.

Step-by-step solution

Chemical Formula for Sodium Chloride

The chemical formula for sodium chloride is derived from its constituent elements: sodium (Na) and chloride (Cl). When these elements form an ionic compound, one sodium ion ( ext{Na}^+) combines with one chloride ion ( ext{Cl}^-) to create the neutral compound sodium chloride. Thus, the chemical formula for sodium chloride is written as NaCl.

Dissolution Process of Sodium Chloride

When sodium chloride dissolves in water, it undergoes a process called dissociation. In this process, the ionic bonds between Na^+ and Cl^- ions are broken by the interaction with the solvent water molecules. Water is a polar solvent, and its molecules surround individual Na^+ and Cl^- ions in a process known as hydration. As a result, the solid structure of NaCl is disrupted, and the ions become solvated, dispersing uniformly throughout the solution. Therefore, the chemical equation representing this dissolution is \[ \text{NaCl}(s) \rightarrow \text{Na}^+(aq) + \text{Cl}^-(aq) \].

Key concepts

Sodium Chloride

Sodium chloride is commonly known as table salt. It plays a significant role in everyday life as well as in various scientific processes.
It is composed of two essential elements, sodium and chlorine, that combine to form the compound. Sodium is a soft, highly reactive metal, while chlorine is a greenish-yellow gas.

• When these elements combine, they form a stable, neutral compound known as sodium chloride, or NaCl.
• This compound is crucial to life on Earth, affecting everything from human health to ocean chemistry.

Chemical Formula

A chemical formula is a way of expressing the components of a chemical compound. It indicates the elements involved and their respective proportions.
For sodium chloride, the chemical formula is NaCl.
This formula tells us several things:

• It consists of one sodium (Na) atom for every one chlorine (Cl) atom.
• The formula reflects the ionic nature of the compound, as sodium and chloride ions form an electrostatic bond to balance their charges.

Understanding chemical formulas is essential for studying chemistry, as they provide information about the composition and structure of molecules.

Dissolution Process

Dissolution is the process through which a solute dissolves in a solvent, forming a solution. When sodium chloride enters water, it undergoes a specific type of dissolution called dissociation.
This refers to the separation of ions that originally formed a solid compound.

• When NaCl dissolves in water, the ionic bonds between sodium ions (\( ext{Na}^+ \)) and chloride ions (\( ext{Cl}^- \)) break.
• Water, being a polar molecule, interacts with these ions, surrounding them in a process known as hydration.

The dissolution of NaCl can be represented by the chemical equation:\[ ext{NaCl}(s) \rightarrow ext{Na}^+(aq) + ext{Cl}^-(aq) \] The ions then evenly disperse in water, creating a homogeneous solution. This is why salt can no longer be seen in the water but the solution will taste salty, reflecting the sodium chloride's presence.

Ionic Bonds

Ionic bonds are strong, attractive forces that hold ions together in a compound. These bonds form when one atom donates an electron to another, resulting in charged particles.

• In sodium chloride, sodium donates an electron to chlorine, resulting in a positive sodium ion (\( ext{Na}^+ \)) and a negative chloride ion (\( ext{Cl}^- \)).
• The opposite charges attract, creating a stable ionic bond.

These forces are why ionic compounds like sodium chloride form crystal structures, where the ions stack neatly and regularly.
Even though ionic bonds are strong, they can be broken in the presence of water, a polar solvent. Water molecules surround and interact with the ions, eventually overcoming the ionic attractions and causing the compound to dissolve.