Question

Classify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte: (a) Sodium permanganate \(\left(\mathrm{NaMnO}_{4}\right)\) (b) Acetic acid \(\left(\mathrm{CH}_{3} \mathrm{COOH}\right)\) (c) Methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\) (d) Calcium acetate \(\left[\mathrm{Ca}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\right]\)

Short answer

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

Step-by-step solution

Understanding Electrolytes

Electrolytes are substances that dissociate into ions when dissolved in water. Strong electrolytes completely dissociate, weak electrolytes partially dissociate, and nonelectrolytes do not dissociate at all.

Classify Sodium Permanganate \(\textbf{\left(\mathrm{NaMnO_{4}}\right)}\)

Sodium permanganate \(\left(\mathrm{NaMnO_{4}}\right)\) is a salt composed of a metal (sodium) and a polyatomic anion (permanganate). Salts of alkali metals and polyatomic ions are typically strong electrolytes because they completely dissociate in water. \[ \mathrm{NaMnO_{4}} (s) \rightarrow \mathrm{Na^{+}} (aq) + \mathrm{MnO_{4}^{-}} (aq) \]

Classify Acetic Acid \(\textbf{\left(\mathrm{CH_{3}COOH}\right)}\)

Acetic acid \(\left(\mathrm{CH_{3}COOH}\right)\) is a weak acid that partially dissociates in water. This partial dissociation means that it is a weak electrolyte. \[ \mathrm{CH_{3}COOH} (aq) \rightleftharpoons \mathrm{CH_{3}COO^{-}} (aq) + \mathrm{H^{+}} (aq) \]

Classify Methanol \(\textbf{\left(\mathrm{CH_{3}OH}\right)}\)

Methanol \(\left(\mathrm{CH_{3}OH}\right)\) is an alcohol and does not dissociate into ions when dissolved in water. Therefore, it is a nonelectrolyte.

Classify Calcium Acetate \(\textbf{\left[\mathrm{Ca}\right(\mathrm{C_{2}H_{3}O_{2}}\right)_{2}\right]}\)

Calcium acetate \(\left[\mathrm{Ca}\right(\mathrm{C_{2}H_{3}O_{2}}\right)_{2}\right]\) is a salt composed of calcium, a metal, and acetate, a polyatomic ion. Salts like these dissociate completely into ions in water, classifying them as strong electrolytes. \[ \mathrm{Ca(C_{2}H_{3}O_{2})_{2}} (s) \rightarrow \mathrm{Ca^{2+}} (aq) + 2 \mathrm{C_{2}H_{3}O_{2}^{-}} (aq) \]

Key concepts

Strong Electrolyte

A strong electrolyte is a substance that completely dissociates into ions when dissolved in water. This means that almost all the substance breaks apart into its constituent ions. Strong electrolytes are usually ionic compounds, such as salts and strong acids or bases. For example, sodium permanganate \((\mathrm{NaMnO_4})\) when dissolved in water yields sodium ions \((\mathrm{Na^+})\) and permanganate ions \((\mathrm{MnO_4^-})\), fully breaking into these ions.

Weak Electrolyte

Unlike strong electrolytes, weak electrolytes only partially dissociate in water. This means that only a fraction of the electrolyte molecules break into ions, leaving the rest intact. Weak acids and bases typically fall under this category. For example, acetic acid \((\mathrm{CH_3COOH})\) in water partially dissociates into acetate ions \((\mathrm{CH_3COO^-})\) and hydrogen ions \((\mathrm{H^+})\). The dissociation is represented by a double arrow \(\rightleftharpoons\) indicating that it is not complete.

Nonelectrolyte

Nonelectrolytes are substances that do not dissociate into ions at all when dissolved in water. This means that they stay as whole molecules and do not produce charged particles. Most organic compounds, such as alcohols and sugars, are nonelectrolytes. For example, methanol \((\mathrm{CH_3OH})\), when dissolved in water, remains as whole methanol molecules and thus does not conduct electricity.

Dissociation of Ions

Dissociation is the process where molecules, especially electrolytes, break apart into ions when they dissolve in water. The extent of dissociation determines whether the substance is a strong, weak, or non-electrolyte. Strong electrolytes dissociate completely, weak electrolytes only partially, and nonelectrolytes do not dissociate at all. Dissociation allows the ions to be free in the solution, which can then conduct electricity.

Chemical Compounds

Chemical compounds are substances formed from two or more elements chemically bonded together. There are different types of chemical compounds, such as ionic compounds and covalent compounds. Ionic compounds, like sodium permanganate \((\mathrm{NaMnO_4})\), tend to dissociate into ions when dissolved in water, forming electrolytes. On the other hand, covalent compounds, such as methanol \((\mathrm{CH_3OH})\), do not dissociate into ions, thus acting as nonelectrolytes. Understanding the nature of these compounds helps in predicting their behavior as electrolytes in solutions.