Question

Classify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte: (a) Hydrogen chloride (HCl) (b) Potassium nitrate \(\left(\mathrm{KNO}_{3}\right)\) (c) Glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) (d) Ammonia \(\left(\mathrm{NH}_{3}\right)\)

Short answer

(a) Strong electrolyte (b) Strong electrolyte (c) Nonelectrolyte (d) Weak electrolyte

Step-by-step solution

Define electrolytes

Electrolytes are substances that dissolve in water to produce a solution that conducts electricity. They can be classified into strong, weak, and nonelectrolytes based on their ability to dissociate in water.

Identify strong electrolytes

Strong electrolytes completely dissociate into ions in water. Examples include most salts, strong acids, and strong bases. For (a) HCl and (b) KNO3: HCl is a strong acid and KNO3 is a salt, both of which dissociate completely in water.

Identify weak electrolytes

Weak electrolytes partially dissociate into ions in water. Examples include weak acids and weak bases. For (d) NH3: NH3 is a weak base and does not dissociate completely in water.

Identify nonelectrolytes

Nonelectrolytes do not dissociate into ions in water and do not conduct electricity. They often include most covalent compounds, particularly organic molecules. For (c) C6H12O6 (glucose): Glucose is a covalent compound that does not ionize in water.

Classify each substance

(a) HCl is a strong electrolyte because it is a strong acid. (b) KNO3 is a strong electrolyte because it is a salt that dissociates completely in water. (c) C6H12O6 (glucose) is a nonelectrolyte because it does not dissociate in water. (d) NH3 is a weak electrolyte because it is a weak base and only partially dissociates in water.

Key concepts

strong electrolyte

Strong electrolytes are substances that completely dissociate into ions when they dissolve in water. This means they break apart into positive and negative ions, allowing the solution to conduct electricity very efficiently. Examples of strong electrolytes include:

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Strong acids like hydrochloric acid (HCl)

Strong bases like sodium hydroxide (NaOH)

Salts like potassium nitrate (KNO3)

When these substances dissolve in water, they fully ionize, resulting in a solution that can easily carry an electric current. Because of this complete dissociation, strong electrolytes are great conductors of electricity. For instance, when HCl is dissolved in water, it separates into H+ ions and Cl- ions, making the solution highly conductive.

weak electrolyte

Weak electrolytes are substances that only partially dissociate into ions in water. Unlike strong electrolytes, they do not completely break apart, so the solution they form is not as good at conducting electricity. Examples include:

• Weak acids like acetic acid (CH3COOH)
• Weak bases like ammonia (NH3)

When weak electrolytes dissolve in water, only a small fraction of the molecules ionize, resulting in fewer ions present in the solution. This limited ionization means that weak electrolytes only allow a small amount of electric current to pass through the solution. For example, NH3 in water partially dissociates into NH4+ and OH- ions, but most of the NH3 remains as molecules, so the solution is only a weak conductor.

nonelectrolyte

Nonelectrolytes are substances that do not dissociate into ions at all when they dissolve in water. As a result, they do not produce a solution that conducts electricity. Common examples include:

• Sugar molecules like glucose (C6H12O6)
• Covalent compounds like ethanol (C2H5OH)

When nonelectrolytes dissolve in water, their molecules disperse throughout the solution, but they remain intact and do not form ions. Because there are no charged particles to carry an electric current, nonelectrolyte solutions are non-conductive. For instance, when glucose dissolves in water, it stays as C6H12O6 molecules, making the solution unable to conduct electricity.

dissociation in water

Dissociation in water refers to the process by which ionic substances separate into ions when they dissolve in water. This process is crucial for the conductivity of electrolyte solutions. Here's how it works:

• When an ionic compound dissolves, the positive and negative ions are surrounded by water molecules.
• Water molecules have partial charges that help to pull the ions apart, allowing them to move freely in the solution.

For instance, when potassium nitrate (KNO3) dissolves, it dissociates into K+ and NO3- ions. This free movement of ions in the water is what enables the solution to conduct electricity.

conductivity in solutions

The conductivity of a solution depends on the presence of free-moving ions. Solutions that conduct electricity well have high concentrations of free ions, while non-conductive solutions lack these ions. The types of substances dissolved in the water play a key role in determining conductivity:

• Strong electrolytes produce high concentrations of ions, making their solutions highly conductive.
• Weak electrolytes produce lower concentrations of ions, resulting in weak conductivity.
• Nonelectrolytes do not produce ions, so their solutions do not conduct electricity at all.

This is why solutions of strong acids, strong bases, and salts (strong electrolytes) are much better at conducting electricity compared to solutions of weak acids, weak bases (weak electrolytes), and non-ionic substances (nonelectrolytes).