Question

The following aqueous solutions were tested with a light bulb conductivity apparatus, as shown in Figure \(4.3 .\) What resultdark, dim, or bright - do you expect from each? (a) \(0.10 \mathrm{M}\) hydrofluoric acid (b) \(0.10 \mathrm{M}\) sodium chloride (c) \(0.10 \mathrm{M}\) glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\)

Short answer

(a) Dim, (b) Bright, (c) Dark.

Step-by-step solution

Understand the Concept of Conductivity

In a light bulb conductivity apparatus, the brightness of the light bulb indicates the electrical conductivity of the solution. Conductivity depends on the presence of ions in solution. Electrolytes, which dissolve to produce ions, can produce a bright or dim light, while non-electrolytes, which do not produce ions, result in no light.

Evaluate Hydrofluoric Acid

Hydrofluoric acid (HF) is a weak acid, which means it only partially ionizes in solution. Due to the presence of some ions, a solution of 0.10 M HF will conduct electricity but with limited conductivity. Therefore, the light bulb would glow dimly.

Evaluate Sodium Chloride

Sodium chloride (NaCl) is a strong electrolyte. It dissociates completely in water, producing a large number of ions (Na⁺ and Cl⁻). This complete dissociation results in high conductivity, so a solution of 0.10 M NaCl will cause the light bulb to glow brightly.

Evaluate Glucose

Glucose (C₆H₁₂O₆) is a non-electrolyte. It dissolves in water but does not dissociate into ions. Because no ions are produced, the solution does not conduct electricity, so the light bulb will remain dark.

Key concepts

Electrolytes

To understand electrical conductivity in solutions, it's important to differentiate between electrolytes and non-electrolytes. **Electrolytes** are substances that dissolve in water to release ions. When these ions move freely in aqueous solutions, they allow the solution to conduct electricity. Common examples of electrolytes include salts, acids, and bases.

Electrolytes can be further classified into strong and weak based on their ability to dissociate into ions in water.

• Strong electrolytes: These are substances that completely dissolve or dissociate into ions. An example is sodium chloride (NaCl), which we know dissolves to produce Na⁺ and Cl⁻ ions, leading to high conductivity. The light bulb in a conductivity apparatus would glow brightly due to the full ionization.
• Weak electrolytes: These partially dissociate into ions, yielding fewer free ions in solution. An example is hydrofluoric acid (HF), which leads to dim light because fewer ions are present.

Recognizing the type of electrolyte in a solution helps predict the level of conductivity and the light bulb's brightness.

Ionization

Ionization is the process by which molecules or compounds form ions in a solution. Let's break it down. When certain compounds dissolve in water, they either fully or partly separate into ions. These ions are charged particles, essential for conducting electricity in water-based (aqueous) solutions.

**Importance of Ionization:**

• The degree of ionization directly affects the solution's electrical conductivity. Strong electrolytes like NaCl ionize fully, introducing plenty of ions and hence, making the light bulb glow brightly.
• Conversely, weak ionization leads to fewer ions. Weak electrolytes like HF only produce some ions, resulting in less conductivity and a dim bulb.

Understanding ionization helps explain why some solutions conduct electricity well while others do not. It's a foundational concept for working with solutions and predicting their behaviors.

Aqueous Solutions

Aqueous solutions are at the heart of many chemical reactions and processes. Simply put, an aqueous solution is a solution where water is the solvent. This makes water an essential carrier for dissolved substances.

**Role in Conductivity:**

• In an aqueous solution, water molecules help dissolve electrolytes by surrounding ion particles and separating them. This process enables ions to spread freely, crucial for conductivity.
• The solution's conductivity depends on the quantity and movement of these ions. A solution of glucose, a non-electrolyte, lacks ions despite being dissolved in water, hence it does not conduct electricity.

By knowing whether a solution is aqueous and whether it contains electrolytes or non-electrolytes, one can predict its ability to conduct an electrical current.

Non-Electrolytes

While discussing solutions and conductivity, non-electrolytes stand out as substances that do not create ions when dissolved. Unlike electrolytes, non-electrolytes dissolve in water without forming charged particles.

This is why solutions of non-electrolytes, such as glucose, do not conduct electricity and why the respective light bulb will not light up at all.

**Characteristics of Non-Electrolytes:**

• They dissolve in water but do not dissociate into ions. This means the molecules remain intact and no free ions are present to carry charge.
• Such solutions' conductivity is practically non-existent, exemplified by glucose (C₆H₁₂O₆). When dissolved, glucose molecules stay whole, non-ionic, leading to no light in a conductivity test.

Understanding these distinctions is crucial for students learning about conductivity in solutions. Recognizing non-electrolytes and their behaviors aids in significant comprehension of how certain substances interact in water.