Question

Molten sodium chloride conducts electricity due to the presence of: (a) Free ions (b) Free molecules (c) Free electrons (d) Atoms of sodium and chlorine

Short answer

Molten sodium chloride conducts electricity due to the presence of free ions.

Step-by-step solution

Understand the Concept

First, let's understand why molten sodium chloride can conduct electricity. Sodium chloride (NaCl) is an ionic compound which, when in solid form, consists of ions that are fixed in a crystalline structure. Solid NaCl cannot conduct electricity because these ions cannot move.

Analyze the Effect of Melting

When NaCl is melted, it transitions into a liquid state. In this state, the rigid ionic structure breaks down, and the ions are free to move.

Identify the Conducting Particles

The free-moving particles that can carry an electrical charge are the ions that were part of the NaCl structure. Specifically, these are the positive sodium ions (Na⁺) and the negative chloride ions (Cl⁻).

Select the Correct Option

Given that molten NaCl conducts electricity due to the presence of ions that can move freely, we conclude that the correct answer is (a) Free ions.

Key concepts

Molten Sodium Chloride

When sodium chloride, commonly known as table salt, is heated to a high temperature, it transforms from a solid to a molten, or liquid, state. In its solid form, the sodium (Na) and chlorine (Cl) atoms are bonded together in a strong ionic lattice, making it a typical example of an ionic compound. However, as heat is applied and it becomes molten, this rigid lattice structure breaks down. This breaking down of the structure allows the ions, which were previously held in place, to move freely within the liquid.

This transition is crucial because it is the freedom of these particles that enables the flow of electrical current. It demonstrates how the physical state of a compound can influence its ability to conduct electricity.

Free Ions

The concept of free ions is central to understanding how molten sodium chloride conducts electricity. In the liquid state, the sodium chloride separates into its constituent ions: sodium ions (Na⁺) and chloride ions (Cl⁻). These ions are no longer held in a fixed structure, allowing them to move independently throughout the molten substance.

The ability of these ions to move freely is critical for conduction.

• The positive sodium ions drift towards a negative electrode.
• Meanwhile, the negative chloride ions move towards a positive electrode.

This movement of charged particles is what constitutes an electric current in the molten salt. It's important to understand that it is this flow of ions, rather than electrons, that allows molten sodium chloride to conduct electricity.

Electrical Conductivity

Conductivity refers to a material's ability to allow the flow of electrical current. In the context of ionic compounds such as sodium chloride, conductivity relies on the presence of charged particles that are free to move. In their solid form, ionic compounds do not conduct electricity because their ions are locked in place within the crystal lattice. However, once the compound is melted, these ions become mobile.

This means:

• Molten ionic compounds, like molten NaCl, can conduct electricity due to the movement of ions.
• Free electrons are not involved in this process; instead, it is the ions that carry the charge.

The transition from solid to liquid significantly affects how these compounds interact with an electrical field, thus highlighting the importance of ionic mobility in conducting electricity.

Ionic Compounds

Ionic compounds are formed from the chemical bonding of metals and non-metals. In these compounds, atoms transfer electrons to each other, creating ions: positively charged cations and negatively charged anions. For example, in sodium chloride, sodium gives up an electron to chlorine, resulting in a positive sodium ion (Na⁺) and a negative chloride ion (Cl⁻). These oppositely charged ions are held together by strong electrostatic forces, forming an ionic bond.

Ionic compounds have distinct properties:

• They form crystal lattices in the solid state.
• They are generally hard and have high melting points due to strong ionic bonds.
• They conduct electricity only when melted or dissolved in water, as their ions become free to move and carry charge.

Understanding how the behavior of ionic compounds changes between solid and liquid forms is key to grasping their role in processes like electrical conduction.