Electrolytes and Nonelectrolytes in Aqueous Solutions

Chapter 12: Solutions

12.2 Electrolytes and Nonelectrolytes

Understanding the behavior of solutes in water is essential for predicting the properties of solutions. Solutes can be classified based on their ability to conduct electricity when dissolved in water, which depends on whether they form ions in solution.

Classification of Solutes

• Electrolytes: Substances that produce ions in water, allowing the solution to conduct an electrical current.

• Nonelectrolytes: Substances that dissolve in water as molecules and do not produce ions; their solutions do not conduct electricity.

Testing for Electrolytes

• An apparatus with a battery, electrodes, and a light bulb can be used to test for the presence of ions in solution.

• The light bulb glows when ions are present, indicating that the solution conducts electricity (i.e., contains electrolytes).

Types of Electrolytes

Electrolytes are further classified based on the extent to which they dissociate in water.

Strong Electrolytes

• Completely dissociate into ions in water.

• Produce only ions in solution.

• Conduct electricity efficiently.

Example:

• Sodium chloride ($\mathrm{NaCl}$):

$\mathrm{NaCl}(s) \xrightarrow{H_2O} \mathrm{Na}^+(aq) + \mathrm{Cl}^-(aq)$

A strong electrolyte in an aqueous solution completely dissociates into ions.

Weak Electrolytes

• Dissolve mostly as molecules, with only a small fraction forming ions.

• Produce a few ions in solution.

• Conduct electricity weakly.

Example:

• Hydrofluoric acid ($\mathrm{HF}$):

$\mathrm{HF}(aq) \rightleftharpoons \mathrm{H}^+(aq) + \mathrm{F}^-(aq)$

A weak electrolyte forms mostly molecules and a few ions in an aqueous solution.

Nonelectrolytes

• Dissolve in water only as molecules.

• Do not produce ions.

• Do not conduct an electric current.

Example:

• Methanol ($\mathrm{CH_3OH}$):

$\mathrm{CH_3OH}(l) \xrightarrow{H_2O} \mathrm{CH_3OH}(aq)$

A nonelectrolyte dissolves in water only as molecules, which do not ionize.

Table: Classification of Solutes in Aqueous Solutions

Type of Solute	In Solution	Type(s) of Particles in Solution	Conducts Electricity?	Examples
Strong electrolyte	Dissociates completely	Only ions	Yes	Ionic compounds (NaCl, KBr, MgCl2, NaNO3); strong acids (HCl, HBr, HNO3, H2SO4)
Weak electrolyte	Dissociates partially	Mostly molecules and a few ions	Weakly	HF, H2O, NH3, HC2H3O2 (acetic acid)
Nonelectrolyte	No dissociation	Only molecules	No	Carbon compounds (CH3OH, C2H5OH, C12H22O11 (sucrose), CH4N2O (urea))

Sample Problem: Identifying Electrolytes and Nonelectrolytes

For each compound, determine the type of particles present in solution and write the equation for its dissolution:

1. Na2SO4(s) (strong electrolyte): Contains only ions in solution. $\mathrm{Na_2SO_4}(s) \xrightarrow{H_2O} 2\mathrm{Na}^+(aq) + \mathrm{SO_4}^{2-}(aq)$

2. Sucrose, C12H22O11(s) (nonelectrolyte): Contains only molecules in solution. $\mathrm{C_{12}H_{22}O_{11}}(s) \xrightarrow{H_2O} \mathrm{C_{12}H_{22}O_{11}}(aq)$

3. Acetic acid, HC2H3O2(l) (weak electrolyte): Contains mostly molecules and a few ions in solution. $\mathrm{HC_2H_3O_2}(l) \rightleftharpoons \mathrm{H}^+(aq) + \mathrm{C_2H_3O_2}^-(aq)$

Review: Key Points

• Electrolytes produce ions in water and conduct electricity; nonelectrolytes do not.

• Strong electrolytes dissociate completely; weak electrolytes dissociate partially.

• Nonelectrolytes dissolve as molecules and do not conduct electrical currents.