Problem 218 - Introductory Chemistry Atoms First

Question

Classify each substance as strong electrolyte, weak electrolyte, or nonelectrolyte: (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) (b) \(\mathrm{KCH}_{3} \mathrm{COO}\) (c) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (e) \(\mathrm{NH}_{3}\) (f) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (g) \(\mathrm{ZnSO}_{4}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{CH}_{3} \mathrm{COOH}\): weak electrolyte (b) \(\mathrm{KCH}_{3} \mathrm{COO}\): strong electrolyte (c) \(\mathrm{H}_{2} \mathrm{SO}_{4}\): strong electrolyte (d) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\): nonelectrolyte (e) \(\mathrm{NH}_{3}\): weak electrolyte (f) \(\mathrm{H}_{3} \mathrm{PO}_{4}\): weak electrolyte (g) \(\mathrm{ZnSO}_{4}\): strong electrolyte

Step 1: (a) Classify \(\mathrm{CH}_{3} \mathrm{COOH}\)

This is acetic acid, which is a weak acid. Hence it is a weak electrolyte.

Step 2: (b) Classify \(\mathrm{KCH}_{3} \mathrm{COO}\)

This is potassium acetate, which is a salt of potassium and acetate ions. Soluble salts are strong electrolytes. Hence this is a strong electrolyte.

Step 3: (c) Classify \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

This is sulfuric acid, which is a strong acid. Strong acids are strong electrolytes. Hence this is a strong electrolyte.

Step 4: (d) Classify \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\)

This is Dichloromethane, a compound which does not ionise in water. Hence it is a nonelectrolyte.

Step 5: (e) Classify \(\mathrm{NH}_{3}\)

This is ammonia, which is a weak base. Weak bases are weak electrolytes. Hence, it is a weak electrolyte.

Step 6: (f) Classify \(\mathrm{H}_{3} \mathrm{PO}_{4}\)

This is phosphoric acid, which is a weak acid. Hence, it is a weak electrolyte.

Step 7: (g) Classify \(\mathrm{ZnSO}_{4}\)

This is zinc sulfate, which is a salt and soluble in water. Hence it is a strong electrolyte.

Key Concepts

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in water. This means they are very efficient at conducting electricity.
For example, when you dissolve potassium acetate ( KCH_{3}COO ) or sulfuric acid ( H_{2}SO_{4} ) in water, they break apart entirely into potassium ions and acetate ions, or hydrogen ions and sulfate ions, respectively. This complete dissociation allows them to carry electrical current effectively, making them strong electrolytes.

• Common strong electrolytes include strong acids, strong bases, and most salts.
• Examples include hydrochloric acid ( HCl ), sodium hydroxide ( NaOH ), and zinc sulfate ( ZnSO_{4} ).

Understanding strong electrolytes is fundamental in chemistry, as they are key players in many reactions and processes.

Weak Electrolytes

Weak electrolytes only partially dissociate into ions in water, which means they do not conduct electricity as efficiently as strong electrolytes.
An example of a weak electrolyte is acetic acid ( CH_{3}COOH ), commonly found in vinegar. When acetic acid is dissolved in water, it splits into ions, but not completely. The result is a solution with fewer free ions, limiting its electrical conductivity.

• Besides acetic acid, weak bases like ammonia ( NH_{3} ) are also weak electrolytes.
• Weak electrolytes typically exhibit equilibrium between the dissociated ions and the undissociated molecules in solution.

This partial ionization is crucial for understanding reactions involving weak acids and bases.

Nonelectrolytes

Nonelectrolytes are substances that do not produce ions when dissolved in water. As a result, they do not conduct electricity at all.
Dichloromethane ( CH_{2}Cl_{2} ) is an excellent example of a nonelectrolyte because it retains its molecular structure in solution, without breaking into ions.

• Typically, most covalent compounds, such as sugars and alcohols, are nonelectrolytes.
• Nonelectrolytes remain unchanged when mixed with water, maintaining their molecular form.

Understanding nonelectrolytes is important to distinguish between substances that can and cannot conduct electricity when dissolved, impacting their use in various chemical and industrial processes.

Chemical Classification

Chemical classification of substances helps us understand their behavior in solutions.
Substances are divided into categories like strong electrolytes, weak electrolytes, and nonelectrolytes based on their ability to dissociate into ions. This classification is based on their physical and chemical properties and how they interact with water.

• Strong electrolytes include many salts, strong acids, and bases because they completely ionize in solution.
• Weak electrolytes include substances that only partially ionize, like acetic acid and ammonia.
• Nonelectrolytes remain intact in solution and do not ionize, like ethanol.

Recognizing these classifications allows chemists and students to predict how substances will behave in different environments, especially aqueous solutions.

Acids and Bases

Acids and bases play a crucial role in chemistry, and their classification into strong and weak categories helps predict their behavior in solutions.
Strong acids, like sulfuric acid ( H_{2}SO_{4} ), and strong bases dissociate completely in water, making them strong electrolytes.
Weak acids, like phosphoric acid ( H_{3}PO_{4} ), and weak bases, like ammonia ( NH_{3} ), only partially ionize, categorizing them as weak electrolytes.

• Acids are substances that donate hydrogen ions ( H^{+} ) in solution.
• Bases are substances that accept hydrogen ions or donate hydroxide ions ( OH^{-} ).

This understanding is foundational for studies in chemistry as it impacts principles like reaction pH, buffer solutions, and titration curves.