Problem 47 - Chemistry The Molecular Science

Question

Identify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte. (a) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (c) \(\mathrm{HNO}_{3}\) (d) \(\mathrm{KOH}\)

Step-by-Step Solution

Answer

(a) Strong electrolyte, (b) Weak electrolyte, (c) Strong electrolyte, (d) Strong electrolyte.

Step 1: Understand Electrolytes Types

An electrolyte is a compound that dissociates into ions when dissolved in water. Strong electrolytes completely dissociate into ions, while weak electrolytes partially dissociate. Nonelectrolytes do not dissociate into ions.

Step 2: Analyze (a) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\)

\(\mathrm{Na}_{2} \mathrm{CO}_{3}\) (sodium carbonate) is an ionic compound that dissociates completely in water to form \(\mathrm{Na}^{+}\) and \(\mathrm{CO}_{3}^{2-}\) ions. Hence, it is a strong electrolyte.

Step 3: Analyze (b) \(\mathrm{H}_{2} \mathrm{CO}_{3}\)

\(\mathrm{H}_{2} \mathrm{CO}_{3}\) (carbonic acid) is a weak acid that only partially dissociates into \(\mathrm{H}^{+}\) and \(\mathrm{HCO}_{3}^{-}\) ions in water. Therefore, it is a weak electrolyte.

Step 4: Analyze (c) \(\mathrm{HNO}_{3}\)

\(\mathrm{HNO}_{3}\) (nitric acid) is a strong acid that completely dissociates into \(\mathrm{H}^{+}\) and \(\mathrm{NO}_{3}^{-}\) ions when dissolved in water. Thus, it is a strong electrolyte.

Step 5: Analyze (d) \(\mathrm{KOH}\)

\(\mathrm{KOH}\) (potassium hydroxide) is a strong base and an ionic compound that completely dissociates into \(\mathrm{K}^{+}\) and \(\mathrm{OH}^{-}\) ions in water. Therefore, it is a strong electrolyte.

Key Concepts

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when they dissolve in water. This full dissociation means that the compound breaks apart entirely, resulting in a solution that presents a high concentration of ions. These ions are excellent conductors of electricity, making the solution electrically conductive.

Several types of compounds are typically strong electrolytes:

• Ionic Compounds: These include many salts, such as sodium chloride (NaCl) and sodium carbonate (Na₂CO₃). Upon dissolving, these compounds separate into cations and anions, their ionic components.
• Strong Acids and Bases: Examples include hydrochloric acid (HCl) and potassium hydroxide (KOH). These substances also completely ionize in water, providing free ions.

Strong electrolytes are crucial in many chemical reactions and industrial processes because of their efficient conductivity and dissociation properties.

Weak Electrolytes

Weak electrolytes are compounds that only partially dissociate into ions in water. This partial dissociation means that in solution, only a small fraction of the solute exists as ions, while the remainder remains as undissociated molecules.

Characteristics and examples include:

• Weak Acids: A classic example is carbonic acid (H₂CO₃). In water, it dissociates slightly to form a small amount of hydrogen ( H⁺ ) and bicarbonate ( HCO₃⁻ ) ions.
• Weak Bases: Ammonia (NH₃) in water forms a limited number of ammonium (NH₄⁺) and hydroxide (OH⁻) ions.

Weak electrolytes lead to solutions with lower electrical conductivity compared to strong electrolytes. These substances are vital when gradual pH changes or specific ion balances are required in a solution.

Nonelectrolytes

Nonelectrolytes are substances that do not dissociate into ions at all when dissolved in water. As a result, these compounds remain as intact molecules in the solution, meaning that they do not conduct electricity because no free ions are present.

Examples of nonelectrolytes include:

• Common Organic Compounds: Many organic compounds, like glucose (C₆H₁₂O₆) and ethanol (C₂H₅OH), dissolve in water but don't produce ions.
• Covalent Compounds: Unlike ionic compounds, covalent compounds typically do not form ions when dissolved. Water itself is a covalent molecule and acts as a nonelectrolyte under standard conditions.

Nonelectrolytes are important in biological systems and various chemical applications where non-conductive solutions are needed. Understanding these compounds helps clarify why some solutions conduct electricity, while others do not.