Problem 37 - Chemistry: The Central Science

Question

Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water: (a) \(\mathrm{H}_{2} \mathrm{SO}_{3}\), (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (ethanol), (c) \(\mathrm{NH}_{3}\), (d) \(\mathrm{KClO}_{3}\), (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\).

Step-by-Step Solution

Answer

(a) \(\mathrm{H}_{2}\mathrm{SO}_{3}\) is a weak electrolyte, as it is a weak acid. (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (ethanol) is a nonelectrolyte, due to its covalent nature. (c) \(\mathrm{NH}_{3}\) (ammonia) is a weak electrolyte, since it is a weak base. (d) \(\mathrm{KClO}_{3}\) (potassium chlorate) is a strong electrolyte, as it is an ionic compound. (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (copper(II) nitrate) is a strong electrolyte, due to its ionic nature.

Step 1: (a) \(\mathrm{H}_{2}\mathrm{SO}_{3}\) (sulfurous acid)

Sulfurous acid is a weak acid; it does not completely dissociate in water. Therefore, it can be classified as a weak electrolyte.

Step 2: (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (ethanol)

Ethanol is a covalent compound, an alcohol, that does not ionize when it dissolves in water. Thus, it is a nonelectrolyte.

Step 3: (c) \(\mathrm{NH}_{3}\) (ammonia)

Ammonia is a weak base; it only partially ionizes in water to form a small amount of ammonium ions (\(\mathrm{NH}_{4}^{+}\)) and hydroxide ions (\(\mathrm{OH}^{-}\)). Therefore, it is a weak electrolyte.

Step 4: (d) \(\mathrm{KClO}_{3}\) (potassium chlorate)

Potassium chlorate is an ionic compound that dissociates completely in water, forming potassium ions (\(\mathrm{K}^{+}\)) and chlorate ions (\(\mathrm{ClO}_{3}^{-}\)). As a result, it is a strong electrolyte.

Step 5: (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (copper(II) nitrate)

Copper(II) nitrate is an ionic compound that dissociates completely in water, forming copper ions (\(\mathrm{Cu}^{2+}\)) and nitrate ions (\(\mathrm{NO}_{3}^{-}\)). Hence, it is a strong electrolyte.

Key Concepts

Nonelectrolytes

Nonelectrolytes are substances that do not conduct electricity when dissolved in water. This is because they do not dissociate into ions. When a nonelectrolyte dissolves, it remains intact as molecules. A classic example of a nonelectrolyte is ethanol (\(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)). Whether in pure form or dissolved, these molecules stay together without breaking into ions.

Here are some key features of nonelectrolytes:

• They form no ions in solution.
• They do not conduct electrical current.
• They are often covalent compounds, like sugars and alcohols.

Understanding nonelectrolytes helps us see why some solutions do not allow for electricity to flow through them. This too is why water, by itself, is typically not a good conductor until substances are added.

Weak Electrolytes

Weak electrolytes partially dissociate into ions in water. This means that only a small percentage of the substance breaks into ions, while the rest remains as molecules. As a result, they conduct electricity, but not very well. An example is ammonia (\(\mathrm{NH}_{3}\)), which in water becomes ammonium ions (\(\mathrm{NH}_{4}^{+}\)) and hydroxide ions (\(\mathrm{OH}^{-}\)).

Key characteristics of weak electrolytes include:

• Partial ionization in solution.
• Weak electrical conductivity compared to strong electrolytes.
• Includes weak acids like acetic acid and weak bases like ammonia.

Recognizing weak electrolytes helps in understanding reactions and behaviors of certain solutions in chemical processes.

Strong Electrolytes

Strong electrolytes completely dissociate into ions when dissolved in water. This means that the solution becomes fully saturated with ions, leading to excellent electrical conductivity. Common examples are ionic compounds like potassium chlorate (\(\mathrm{KClO}_{3}\)) and copper(II) nitrate (\(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\)).

Attributes of strong electrolytes include:

• Complete ionization in water.
• High electrical conductivity.
• Usually strong acids, strong bases, or fully soluble salts.

Understanding strong electrolytes is crucial for working with solutions that need robust electrical properties, such as battery solutions or electrolysis processes.

Dissociation in Water

Dissociation in water refers to the process where compounds break into their component ions when dissolved. This process is central to understanding how chemicals behave in aqueous solutions. Ionic compounds, like those often classed as strong electrolytes, typically dissociate completely.

Main points about dissociation:

• Affects a substance's ability to conduct electricity.
• Involves separation into positive and negative ions.
• Each type of compound—strong, weak, and non-electrolyte—dissociates differently.

This concept is fundamental in chemistry, as it explains why substances behave differently when added to water and how their ionic nature determines their electrolytic strength.