Properties of Acids and Bases: Empirical Definitions, Nomenclature, and Arrhenius Theory

Introduction to Acids and Bases

• Acids and bases are central to chemistry affecting daily life.
• Food consumption primarily involves acidic substances.
• Many household cleaners are basic in nature.

Common Household Acids and Bases and Their Uses

• Acetic acid ($CH_3COOH_{(aq)}$):
  • Used for flavoring and as a preservative.
• Citric acid ($C_3H_5O(COOH)_3(aq)$):
  • Used for flavoring.
• Ascorbic acid ($H_2C_6H_6O_6(aq)$):
  • Known as Vitamin C; used as a nutritional supplement.
• Sodium hydroxide ($NaOH_{(aq)}$):
  • Used as an oven and drain cleaner.
• Ammonia ($NH_3(aq)$):
  • Used as a household cleaner.
• Sodium carbonate ($Na_2CO_3(aq)$):
  • Used in fire extinguishers, baking soda, and as a mild antacid.

Review of Nomenclature of Acids and Bases

• Rules for naming are governed by the International Union of Pure and Applied Chemistry (IUPAC).

Naming Acids

• Acids have been known for hundreds of years, often by familiar classical names.
• IUPAC names are often less commonly used than classical names in professional practice.
• Students are required to know both classical and IUPAC naming systems.
• Examples for nomenclature:
  • $HBr_{(aq)}$
  • $H_2SO_4(aq)$
  • $HNO_2(aq)$

Naming Bases

• Most common bases are formed when a metal (primarily from Groups 1A and 2A) bonds with a hydroxide ion.
• The naming procedure involves two steps:
  1. Name the metal cation first; it retains its name as listed in the Periodic Table.
  2. The polyatomic ion hydroxide ($OH^-$) also retains its name.
• Examples of bases for naming:
  • Lithium hydroxide: $LiOH_{(s)}$
  • Beryllium hydroxide: $Be(OH)_2(s)$
  • Nickel (III) hydroxide: $Ni(OH)_3(s)$

Empirical (Observable) Definitions of Acids and Bases

Solutions can be categorized by observable properties that identify them as acidic, basic, or neutral.

Characteristics of Acids

• Taste: Sour.
• pH (Aqueous): Less than $7$.
• Ionic Composition: Aqueous solutions contain hydrogen ions ($H^+$).
• Electrical Properties: They are electrolytes that conduct electricity.
• Reactivity: React with metals specifically zinc ($Zn$) or magnesium ($Mg$) to produce hydrogen gas ($H_{2(g)}$).
• Indicator Test: Turn blue litmus paper red.
• Neutralization: React with bases to produce salt and water.

Characteristics of Bases

• Taste: Bitter.
• pH (Aqueous): Greater than $7$.
• Ionic Composition: Aqueous solutions contain hydroxide ions ($OH^-$).
• Physical Sensation: Have a soapy, slippery feeling on the skin.
• Electrical Properties: They are electrolytes that conduct electricity.
• Indicator Test: Turn red litmus paper blue.
• Neutralization: React with acids to produce salt and water.

Characteristics of Neutral Solutions

• pH (Aqueous): Equal to $7$.
• Ionic Balance: The amounts of hydrogen ions ($H^+$) and hydroxide ions ($OH^-$) are equal.

Methods for Distinguishing Solutions

Acids and bases can be differentiated using three primary empirical tools:

• Litmus Paper:
  • Blue to red indicates an acidic solution.
  • Red to blue indicates a basic solution.
• pH Meter:
  • $pH < 7$: Acidic.
  • $pH = 7$: Neutral.
  • $pH > 7$: Basic.
• Conductivity Tester:
  • Used to distinguish between four types of solutes: acids, bases, neutrals, and molecular compounds.

Arrhenius Theory (1887)

Developed by Svante Arrhenius in 1887, this theory provides a molecular-level explanation for the behavior of acids and bases.

Theoretical Framework

• Proposes that when a substance dissolves, its particles separate from each other and enter the solution.
• Acids and bases share properties with molecular and ionic substances while possessing unique characteristics.

Electrolytes vs. Non-electrolytes

• Electrolytes:
  • Definition: Aqueous compounds capable of conducting electricity.
  • Examples: Soluble ionic compounds, bases (which dissociate), and acids (which ionize).
• Non-electrolytes:
  • Definition: Aqueous compounds that cannot conduct electricity.
  • Examples: Molecular compounds and insoluble ionic compounds (which undergo dispersion).

Arrhenius Acids and Ionization

• Arrhenius Acid Definition: A substance that ionizes in water to produce hydrogen ions ($H^+_{(aq)}$).
• Litmus Result: Red litmus paper stays red; blue litmus paper turns red.

Ionization Equations (Examples)

• Hydrobromic acid:
  • $HBr_{(aq)} \rightarrow H^+_{(aq)} + Br^-_{(aq)}$
• Nitric acid:
  • $HNO_3(aq) \rightarrow H^+_{(aq)} + NO_3^-(aq)$
• Formic acid:
  • $HCOOH_{(aq)} \rightarrow H^+_{(aq)} + HCOO^-_{(aq)}$

Arrhenius Bases and Dissociation

• Arrhenius Base Definition: An ionic compound that dissociates in water to produce hydroxide ions ($OH^-_{(aq)}$).
• Litmus Result: Blue litmus paper stays blue; red litmus paper turns blue.

Dissociation Equations (Examples)

• Calcium hydroxide:
  • $Ca(OH)_2(s) \rightarrow Ca^{2+}_{(aq)} + 2OH^-_{(aq)}$
• Iron (III) hydroxide:
  • $Fe(OH)_3(s) \rightarrow Fe^{3+}_{(aq)} + 3OH^-_{(aq)}$
• Sodium hydroxide:
  • $NaOH_{(s)} \rightarrow Na^+_{(aq)} + OH^-_{(aq)}$

Activity and Practice Problems

Qualitative Questions

1. Identify two acids and two bases found at home.
2. List three empirical characteristics of acids.
3. List three empirical characteristics of bases.
4. Define an electrolyte and provide an example.
5. Define a non-electrolyte and provide an example.
6. Define an Arrhenius acid and provide an example.
7. Define an Arrhenius base and provide an example.
8. Compare dissociation and ionization by listing similarities and differences.
9. Explain the Arrhenius theory for:
   • a. An acid turning blue litmus red.
   • b. A base turning red litmus blue.

Acid and Base Nomenclature Practice

A. Classical and IUPAC names for acids:

• i. $H_2SO_3(aq)$ (Found in acid rain)
• ii. $HF(aq)$ (Used for etching glass)
• iii. $H_2CO_3(aq)$ (Found in carbonated beverages)
• iv. $H_2S(aq)$ (Rotten egg odor)
• v. $H_3PO_4(aq)$ (Rust remover)
• vi. $HCN(aq)$ (Rat killer)
• vii. $H_3BO_3(aq)$ (Insecticide)
• viii. $C_6H_5COOH(aq)$ (Preservative)

B. Formulas for the following acids:

• i. Butanoic acid
• ii. Oxalic acid
• iii. Sulfuric acid
• iv. Hydroiodic acid
• v. Perchloric acid

C. IUPAC names for the following bases:

• i. $NaOH_{(s)}$
• ii. $Ca(OH)_2(s)$
• iii. $KOH_{(s)}$
• iv. $Sr(OH)_2(s)$
• v. $Mn(OH)_4(s)$

D. Formulas for the following bases:

• i. Lithium hydroxide
• ii. Magnesium hydroxide
• iii. Barium hydroxide
• iv. Cesium hydroxide
• v. Iron (III) hydroxide

Ionization and Dissociation Equations

Write equations for the follow substances:

• a. Hydroiodic acid
• b. Sulfuric acid
• c. Oxalic acid
• d. Nickel (III) hydroxide
• e. Calcium hydroxide
• f. Strontium hydroxide

Classification Practice

Based on chemical formulas, classify the following as acid, base, or neutral:

• a. $H_2SO_3(aq)$
• b. $NaOH_{(aq)}$
• c. $CH_3OH_{(aq)}$
• d. $C_2H_5COOH_{(aq)}$
• e. $NaCH_3COO_{(aq)}$
• f. $Ba(OH)_2(aq)$