Problem 38 - Chemistry: The Central Science in SI Units, Global Edition

Question

Classify each of the following aqueous solutions as a nonelectrolyte, weak electrolyte, or strong electrolyte: (a) \(\mathrm{PbCl}_{2}\), (b) \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\) (c) \(\mathrm{CsOH}\), (d) \(\mathrm{H}_{2} \mathrm{~S},\) (e) \(\mathrm{CrCl}_{2}\) (f) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{PbCl}_{2}\): weak electrolyte; (b) \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\): nonelectrolyte; (c) \(\mathrm{CsOH}\): strong electrolyte; (d) \(\mathrm{H}_{2} \mathrm{~S}\): weak electrolyte; (e) \(\mathrm{CrCl}_{2}\): strong electrolyte; (f) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\): strong electrolyte.

Step 1: (a) Classify \(\mathrm{PbCl}_{2}\)

: \(\mathrm{PbCl}_{2}\) is an ionic compound (lead(II) chloride), and ionic compounds are usually strong electrolytes. However, \(\mathrm{PbCl}_{2}\) is not very soluble in water, so it dissociates slightly, making it a weak electrolyte.

Step 2: (b) Classify \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\)

: \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\), trimethylamine, is a covalent compound that does not dissociate into ions when dissolved in water. Therefore, it is a nonelectrolyte.

Step 3: (c) Classify \(\mathrm{CsOH}\)

: \(\mathrm{CsOH}\), cesium hydroxide, is an ionic compound and it dissociates completely in water. Alkali metal hydroxides are strong electrolytes, so \(\mathrm{CsOH}\) is a strong electrolyte.

Step 4: (d) Classify \(\mathrm{H}_{2} \mathrm{~S}\)

: \(\mathrm{H}_{2} \mathrm{S}\), hydrogen sulfide, is a covalent compound. It is a weak acid that ionizes slightly in water, producing hydrogen ions (\(H^+\)) and sulfide ions (\(S^{2-}\)). Therefore, \(\mathrm{H}_{2}\mathrm{S}\) is a weak electrolyte.

Step 5: (e) Classify \(\mathrm{CrCl}_{2}\)

: \(\mathrm{CrCl}_{2}\), chromium(II) chloride, is an ionic compound that dissociates completely in water, producing chromium ions (\(Cr^{2+}\)) and chloride ions (\(Cl^-\)). Therefore, \(\mathrm{CrCl}_{2}\) is a strong electrolyte.

Step 6: (f) Classify \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\)

: \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\), nickel(II) acetate, is an ionic compound that dissociates completely in water, producing nickel ions (\(Ni^{2+}\)) and acetate ions (\(CH_{3}COO^-\)). Therefore, \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) is a strong electrolyte.

Key Concepts

Nonelectrolyte

Nonelectrolytes are compounds that do not produce ions when dissolved in water. This means they do not conduct electricity because there are no charged particles available to carry the current. Nonelectrolytes typically consist of molecules, rather than ions. Most covalent compounds fall into this category, which includes many organic substances like sugars and alcohols.
One example is trimethylamine, ext{N(CH}_3)_3, which can dissolve in water but remains as whole molecules. Since these molecules do not dissociate into ions, no electricity is conducted.

• Do not dissociate into ions.
• Do not conduct electricity.
• Often covalent compounds like organic substances.

Weak Electrolyte

Weak electrolytes partially dissociate into ions when dissolved in water. This incomplete ionization means that only a fraction of the solute exists as ions, resulting in a weak ability to conduct electricity. Weak acids and weak bases are common examples of weak electrolytes.
Consider the case of ext{H}_2 ext{S}, or hydrogen sulfide. It ionizes slightly in water, producing some hydrogen ions ( ext{H}^+ ) and sulfide ions ( ext{S}^{2-} ), but not enough to conduct electricity strongly.

• Partial ionization in water.
• Weak electrical conductivity.
• Includes weak acids like hydrogen sulfide.

Strong Electrolyte

Strong electrolytes dissociate completely into ions when added to water, yielding solutions that conduct electricity very well. Because of this full ionization, strong electrolytes are often ionic compounds or strong acids.
Examples include ionic compounds like cesium hydroxide ( ext{CsOH} ) and chromium(II) chloride ( ext{CrCl}_2 ). Both dissociate fully in solution, ensuring maximum conductivity.

• Complete dissociation into ions.
• Excellent electrical conductivity.
• Usually ionic compounds or strong acids/bases.