Aqueous Solutions: Classification, Solubility, and Electrolytes

Aqueous Solutions

Classification of Compounds: Molecules, Acids, and Bases

In chemistry, substances that dissolve in water (aqueous solutions) can be classified based on their composition and properties. Understanding these classifications is essential for predicting chemical behavior in solution.

• Ionic Compounds: Contain a metal and a nonmetal or a polyatomic ion (e.g., NaCl, CuCl2, NH4OH).

• Covalent Compounds: Contain only nonmetals and no polyatomic ions (e.g., H2, CH4).

• Acids: Typically start with "H" (e.g., HCl, H2SO4).

• Bases: Typically end with "OH" (e.g., NaOH, KOH).

Compounds can further be classified as salts, molecules, acids, or bases based on their chemical structure and behavior in water.

• Example: HC2H3O2 (Acid), CO2 (Molecule), NaCl (Salt)

Solubility in Water

Whether a chemical dissolves in water depends on its structure and the presence of certain ions. The solubility of a substance is indicated as aqueous (aq) if it dissolves, or solid (s) if it does not.

• General Solubility Rules:

  • Compounds containing alkali metal ions (Group 1 elements) are soluble.

  • Compounds containing ammonium ion (NH4+) are soluble.

  • Compounds containing nitrate ion (NO3-) are soluble.

• Some substances require a solubility chart to determine if they dissolve in water.

• Insoluble substances do not dissolve and remain as solids.

Additional info: Covalent substances often do not ionize in water and may not dissolve unless they can form hydrogen bonds or react with water.

Electrolytes and Conductivity

When substances dissolve in water, they may produce ions, which can conduct electricity. The ability to conduct electricity depends on the degree of ionization.

• Strong Electrolytes: Substances that completely dissociate into ions in water (e.g., NaCl, HCl). These solutions conduct electricity well.

• Weak Electrolytes: Substances that partially dissociate into ions (e.g., acetic acid, NH3). These solutions conduct electricity weakly.

• Nonelectrolytes: Substances that do not produce ions in solution (e.g., sugar, most covalent compounds). These do not conduct electricity.

Example: NaCl in water is a strong electrolyte; glucose in water is a nonelectrolyte.

Summary Table: Classification and Solubility

Type	Example	Solubility in Water	Electrolyte Type
Ionic Compound	NaCl	Soluble (aq)	Strong Electrolyte
Covalent Compound	CH4	Insoluble (s)	Nonelectrolyte
Acid	HCl	Soluble (aq)	Strong Electrolyte
Base	NaOH	Soluble (aq)	Strong Electrolyte
Weak Acid	HC2H3O2	Soluble (aq)	Weak Electrolyte