020725 CHEM 102 SP25 Unit 05A pre

Unit 5A: Electrolytes

Definition of Electrolytes

• Electrolyte: A substance that dissolves in water to form a solution that conducts electricity.

• Nonelectrolyte: A substance that dissolves in water but does not conduct electricity.

Characteristics of Nonelectrolytes

• Most soluble molecular compounds remain intact in water.

• Example:

  • C12H22O11 (s) ➔ C12H22O11 (aq)

Strong Electrolytes

• Strong electrolytes completely dissociate into ions in an aqueous solution.

• This dissociation can occur through:

  • Dissociation: The physical process of ionic compounds separating into ions.

  • Ionization: The chemical process when strong acids react with water to yield ions at 100% yield.

Ionic Compounds as Strong Electrolytes

• All ionic compounds are strong electrolytes because they completely dissociate in water.

• Example:

  • NaCl(s) ➔ Na+(aq) + Cl-(aq)

Strong Acids as Strong Electrolytes

• Strong acids ionize completely upon reaction with water.

• Example reactions include:

  • H2O(l) + HCl(g) ➔ H3O+(aq) + Cl-(aq)

  • Shorthand: HCl(aq) ➔ H+(aq) + Cl-(aq)

• Common strong acids to memorize:

  • HBr (hydrobromic acid)

  • HCl (hydrochloric acid)

  • HI (hydroiodic acid)

  • HNO3 (nitric acid)

  • HClO4 (perchloric acid)

  • H2SO4 (sulfuric acid)

Weak Acids as Weak Electrolytes

• Weak acids have partial ionization in water (less than 100%).

• These solutions consist of both unreacted acid molecules and ions.

• Example reaction:

  • H2O(l) + HF(aq) ⇌ H3O+(aq) + F-(aq)

• Percent ionization is usually <5% for weak acids.

Identifying Weak Acids

• If it is not listed as a strong acid, it is likely a weak acid.

• Compounds that start with "H" indicate acidity (e.g., acetic acid: HC2H3O2).

• Carboxylic acids are categorized as weak acids.

  • Example: CH3COOH (acetic acid)

  • Reactions:

  • HC2H3O2(aq) ⇄ H+(aq) + C2H3O2-(aq)

  • CH3COOH(g) + H2O(l) ⇌ H3O+(aq) + CH3COO-(aq)

Summary of Acids

• Binary acids: Hydrogen + nonmetal (e.g., HCl, HBr).

• Oxyacids: Hydrogen + polyatomic ion (e.g., HNO3).

• Carboxylic acids: Organic compounds with a specific arrangement of atoms (e.g., CH3COOH).

Ionic Compounds as Bases

• A base is any substance that dissolves in water to yield hydroxide ions (OH-).

• Commonly formed from alkali or alkaline earth metals with OH-.

• Example:

  • NaOH(aq) ➔ Na+(aq) + OH-(aq)

  • Ba(OH)2(s) ➔ Ba+(aq) + 2 OH-(aq)

• These hydroxide compounds are considered strong bases and dissociate completely in water.

Alcohols

• Alcohols are organic compounds containing the –OH functional group directly bonded to carbon.

• They act as nonelectrolytes.

• Example: CH3CH2OH(l) remains unchanged in the aqueous solution.

Molecular Compounds that Form Weak Bases

• Weak bases typically involve partial ionization and often contain nitrogen with a lone pair.

• Examples include ammonia (NH3).

Amines

• Amines are compounds containing C-N bonds, with nitrogen containing a lone pair.

• Classification of amines:

  • Primary amines: One C-N bond.

  • Secondary amines: Two C-N bonds.

  • Tertiary amines: Three C-N bonds.

Ionic vs Molecular Bases

• Ionic Bases:

  • Strong electrolytes through dissociation.

  • Basic solution due to hydroxide ion release.

  • Example: NaOH(s) ➔ Na+(aq) + OH-(aq)

• Molecular Bases:

  • Weak electrolytes through partial ionization.

  • Basic solution due to formation of hydroxide ions.

  • Example: NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)

Electrolyte Summary

• Strong Electrolyte: 100% ion formation (ALL IONS).

• Weak Electrolyte: <100% ion formation (FEW IONS).

• Nonelectrolyte: 0% ion formation (NO IONS).

Important Notes on Solutions

• Ionic compounds dissociate completely and are strong electrolytes.

• Strong acids ionize completely to form strong electrolytes.

• Weak acids and bases partially ionize and are weak electrolytes.

• Covalent compounds may not form ions in solution and are considered nonelectrolytes.

Example Compounds

• KOH: Ionic compound and strong base.

  • Dissociates completely: KOH(s) ➔ K+(aq) + OH-(aq)

  • Strong electrolyte.

• HNO2: Covalent compound being a weak acid.

  • Partially ionizes: HNO2(aq) ⇌ H+(aq) + NO2-(aq)

  • Weak electrolyte.

• Alcohols (e.g., CH3CH2OH): Remain unchanged in solution; classified as nonelectrolytes.

• Covalent Compounds (e.g., C6H12O6): Do not ionize; classified as nonelectrolytes.

• CH3NH2: Covalent compound, weak base, partially ionizes.

  • Reaction: CH3NH2(aq) ⇌ CH3NH3+(aq) + OH-(aq)

• Fe(NO3)2: Ionic compound that completely dissociates.

  • Dissociation: Fe(NO3)2(aq) ➔ Fe2+(aq) + 2NO3-(aq)

• CH3COOH: A weak acid (acetic acid) that partially ionizes:

  • CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)

Final Notes

• An understanding of dissociation, ionization, and the classification of acids and bases is vital.

• Memorization of common strong acids and their behaviors in solutions will aid in studies.