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) H2SO3 is a weak electrolyte, as it is a weak acid that partially dissociates in water. (b) C2H5OH (ethanol) is a nonelectrolyte, as it does not dissociate into ions when dissolved in water. (c) NH3 (ammonia) is a weak electrolyte, as it is a weak base and partially ionizes in water. (d) KClO3 (potassium chlorate) is a strong electrolyte, as it is an ionic compound that completely dissociates in water. (e) Cu(NO3)2 (copper(II) nitrate) is a strong electrolyte, as it is an ionic compound that completely dissociates in water.

Step 1: (a) Classifying H2SO3

H2SO3 is sulfurous acid. Acids tend to dissociate in water releasing H+ ions. Sulfurous acid is a weak acid, meaning it only partially dissociates in water. Therefore, H2SO3 is a weak electrolyte.

Step 2: (b) Classifying C2H5OH (ethanol)

Ethanol (C2H5OH) is an organic compound that does not dissociate into ions when dissolved in water. Ethanol molecules remain intact upon dissolution in water and hence, it does not conduct electricity. Therefore, ethanol is a nonelectrolyte.

Step 3: (c) Classifying NH3

NH3, ammonia, is a weak base. When dissolved in water, it reacts with water to form a small amount of ammonium ions (NH4+) and hydroxide ions (OH-). Since it only partially ionizes in water, ammonia is a weak electrolyte.

Step 4: (d) Classifying KClO3

KClO3, potassium chlorate, is an ionic compound. Upon dissolution in water, it completely dissociates into potassium ions (K+) and chlorate ions (ClO3-). Since it completely ionizes in water, KClO3 is a strong electrolyte.

Step 5: (e) Classifying Cu(NO3)2

Cu(NO3)2, copper(II) nitrate, is an ionic compound. When dissolved in water, it completely dissociates into copper(II) ions (Cu2+) and nitrate ions (NO3-). Due to its complete ionization in water, Cu(NO3)2 is a strong electrolyte.

Key Concepts

Nonelectrolyte

A nonelectrolyte is a substance that does not produce ions when dissolved in water. This means it does not conduct electricity because electricity in solutions is conducted through the movement of ions.
Examples of nonelectrolytes typically include organic compounds such as sugars, fats, and alcohols like ethanol (C2H5OH). When ethanol is mixed with water, it remains intact without releasing or taking in ions from the water.
This can be a puzzling concept, because many nonelectrolytes are still soluble in water; they just don't break down into charged particles necessary for electrical conductivity.

Weak Electrolyte

Substances that only partially dissociate into ions in water are known as weak electrolytes. They release ions into the solution but not completely, resulting in a small degree of electrical conductivity.
Weak acids like sulfurous acid (H2SO3) and weak bases such as ammonia (NH3) are prime examples of weak electrolytes. With weak acids, only a few of the molecules release H+ ions into the solution. Meanwhile, ammonia reacts with water to form a limited amount of ammonium (NH4+) and hydroxide ions (OH-).
The key takeaway here is that weak electrolytes result in a solution where there are intact molecules as well as ions. Understanding the balance between the unchanged substances and the ions they form is essential for predicting the behavior of weak electrolytes.

Strong Electrolyte

The term 'strong electrolyte' describes substances that completely dissociate into ions when dissolved in water. This total dissociation allows the solution to conduct electricity well.
Strong electrolytes include most ionic compounds, such as salts, strong acids, and strong bases. Potassium chlorate (KClO3) and copper(II) nitrate (Cu(NO3)2) represent strong electrolytes. When these compounds are encountered in a solution, they break apart fully into ions—potassium ions (K+) and chlorate ions (ClO3-) in the case of KClO3, and copper(II) ions (Cu2+) and nitrate ions (NO3-) for Cu(NO3)2.
It's important for students to recognize that these substances are not present in the solution as molecules but rather as separate positively and negatively charged ions. This fundamental understanding is crucial when making predictions about conductivity and the outcomes of chemical reactions.

Dissociation in Water

Dissociation in water refers to the process of breaking down a compound into its component ions. This process is fundamental to the concept of electrolytes and their ability to conduct electricity.
The degree of dissociation determines whether a substance is a strong, weak, or nonelectrolyte. For example, strong electrolytes dissociate completely, weak electrolytes partially, and nonelectrolytes not at all.
It's also worth noting that the nature of the substance, the temperature of the water, and the presence of other substances can influence the dissociation process. Understanding this topic is essential because many chemical reactions, including reactions crucial to biological processes or industrial operations, occur in aqueous solutions.

Ionic Compounds

Ionic compounds are formed by the chemical bonding of positively charged ions, known as cations, and negatively charged ions, called anions. These compounds have high melting points and conduct electricity when dissolved in water or in a molten state.
The reason for their ability to conduct electricity lies in their structure: in solid form, ions are held together in a lattice, but when dissolved in water, the ionic bonds break and the ions become free to move. This ability to produce free-moving ions makes them strong electrolytes.
A common misconception is that all ionic compounds are strong electrolytes. However, certain ionic compounds do not dissolve well in water, and their conductivity might be lower as a result. Understanding ionic compounds and their behavior in water helps students in predicting outcomes in reactions and understanding properties like boiling points and electrical conductivity.