Question

Classify each of the following aqueous solutions as a nonelectrolyte, weak electrolyte, or strong electrolyte: (a) \(\mathrm{HClO}_{4}\) (b) \(\mathrm{HNO}_{3}\), (c) \(\mathrm{NH}_{4} \mathrm{Cl}\), (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) (acetone), (e) \(\operatorname{CoSO}_{4}\), (f) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) (sucrose).

Short answer

(a) HClO4: strong electrolyte, (b) HNO3: strong electrolyte, (c) NH4Cl: strong electrolyte, (d) CH3COCH3 (acetone): nonelectrolyte, (e) CoSO4: strong electrolyte, (f) C12H22O11 (sucrose): nonelectrolyte.

Step-by-step solution

(a) HClO4:

HClO4 (perchloric acid) is a strong acid, which means it completely ionizes in water. Therefore, HClO4 is a strong electrolyte.

(b) HNO3:

HNO3 (nitric acid) is another strong acid and dissociates completely when dissolved in water. HNO3 is classified as a strong electrolyte.

(c) NH4Cl:

NH4Cl (ammonium chloride) is a salt that dissolves and dissociates completely into ions in water. Therefore, NH4Cl is a strong electrolyte.

(d) CH3COCH3 (acetone):

Acetone (CH3COCH3) is an organic compound that does not dissociate into ions when dissolved in water. As it doesn't produce ions, it is a nonelectrolyte.

(e) CoSO4:

CoSO4 (cobalt(II) sulfate) is a salt that dissociates into ions when dissolved in water. CoSO4 is considered a strong electrolyte.

(f) C12H22O11 (sucrose):

Sucrose (C12H22O11) is a sugar molecule that does not dissociate into ions when dissolved in water. Thus, it is categorized as a nonelectrolyte.

Key concepts

Strong Electrolytes

Substances that fully dissociate into ions when dissolved in water are classified as strong electrolytes. This complete ionic dissociation allows the solution to conduct electricity very efficiently, hence the term 'electrolyte'. Examples of strong electrolytes include strong acids like hydrochloric acid (\r\(HCl\)) and perchloric acid (\r\(HClO_4\)), strong bases like sodium hydroxide (\r\(NaOH\)), and most salts such as sodium chloride (\r\(NaCl\)) and ammonium chloride (\r\(NH_4Cl\)). These substances break apart into their respective cations and anions fully, resulting in a solution teeming with charge carriers. A simple rule of thumb is that any compound that is a strong acid, strong base, or a soluble salt is likely a strong electrolyte.

Weak Electrolytes

Weak electrolytes partially dissociate into ions in an aqueous solution, which means they only generate a small amount of ions. As a result, weak electrolytes conduct electricity, but not as well as strong electrolytes. Examples of weak electrolytes are weak acids like acetic acid (\r\(CH_3COOH\)) and weak bases such as ammonia (\r\(NH_3\)). The presence of undissociated molecules alongside the ions is a hallmark feature of weak electrolyte solutions. For instance, when they dissolve in water, only some of the molecules ionize, while the rest remain intact. This incomplete ionization is what imparts these solutions with their 'weak' conductivity characteristics.

Nonelectrolytes

In contrast to electrolytes, nonelectrolytes do not produce ions at all in aqueous solutions. Because of this, nonelectrolyte solutions do not conduct electricity. Common examples of nonelectrolytes are most organic compounds like sugars (e.g., sucrose \r\(C_{12}H_{22}O_{11}\)) and solvents like ethanol (\r\(C_2H_5OH\)). If you dissolve sucrose in water, the solution remains non-conductive because the sucrose molecules do not break into ions; they simply dissolve due to the polar nature of water, which allows these molecules to disperse uniformly within the solution.

Aqueous Solutions

An aqueous solution is created when a substance (solvent) is dissolved in water (solvent). Water, being a polar molecule, is capable of dissolving a wide range of substances due to its ability to stabilize ions and polar molecules. The 'aqueous' part of the term signifies that water is the medium of the solution. Understanding the polarity and the resultant solvation processes helps clarify why certain ionic compounds dissociate to a greater extent, why some substances only partially dissociate, and why others do not dissociate at all. When discussing the solubility of various compounds, the focus is on how they behave in aqueous solutions, as this information is critical in chemical reactions and applications, including electrolytes.

Ionic Dissociation

Ionic dissociation is the process where an ionic compound separates into its constituent ions when dissolved in a solvent like water. This process is fundamental to understand electrolytes because it explains how the conductivity of a solution arises. Ionic compounds such as salts, when placed in water, can dissociate to release cations (positively charged ions) and anions (negatively charged ions) that freely move in the solution. For example, table salt (\r\(NaCl\)) dissociates into \r\(Na^+\) and \r\(Cl^-\) ions in water. The extent of ionic dissociation varies from complete (in strong electrolytes) to partial (in weak electrolytes), and it's this characteristic that influences the electrical conductivity and chemical reactions of the solution.