Acids and Bases Study Notes

General Properties of Acids

  • Taste: Acids typically have a sour taste.
  • Reactivity: They can dissolve many metals.
  • Neutralization: Acids neutralize bases.
  • Litmus Test: Acids turn blue litmus paper red.
  • Example: Acetic acid is commonly known as vinegar.

Common Acids and Their Uses

  • Hydrochloric acid (HCl): Used in metal cleaning, food preparation, ore refining, and is a primary component of stomach acid.
  • Sulfuric acid (H2SO4): Used in fertilizer and explosives manufacturing, dye and glue production, automobile batteries, and electroplating of copper.
  • Nitric acid (HNO3): Used in fertilizer and explosives manufacturing, dye and glue production.
  • Acetic acid (HC2H3O2): Used in plastic and rubber manufacturing, food preservation, and as a component of vinegar.
  • Citric acid (H3C6H5O7): Found in citrus fruits like lemons and limes; used to adjust pH in foods and beverages.
  • Carbonic acid (H2CO3): Present in carbonated beverages.
  • Hydrofluoric acid (HF): Used in metal cleaning, glass frosting, and etching.
  • Phosphoric acid (H3PO4): Utilized in fertilizer manufacturing, biological buffering, and beverage preservation.

Structure of Organic Acids - Carboxylic Acids

  • Functional Group: Carboxylic acids contain a COOH group.
    • Acetic acid: HC2H3O2
    • Citric acid: H3C6H5O7
  • Acidity: Only the hydrogen atom in the COOH group is acidic.
  • Example Structure: H—O—C (carbon backbone) || O

General Properties of Bases

  • Taste: Bases typically have a bitter taste.
  • Safety: Many bases can be poisonous.
  • Feel: Bases feel slippery to the touch.
  • Neutralization: They can neutralize acids.
  • Litmus Test: Bases turn red litmus paper blue.

Common Bases and Their Uses

  • Sodium hydroxide (NaOH): Used in petroleum processing, soap, and plastic manufacturing.
  • Potassium hydroxide (KOH): Used in cotton processing, electroplating, soap production, and batteries.
  • Sodium bicarbonate (NaHCO3): Commonly known as baking soda, used as an antacid and source of CO2.
  • Sodium carbonate (Na2CO3): Utilized in glass and soap manufacturing, general cleaning.
  • Ammonia (NH3): Employed in detergents, fertilizers, explosives manufacturing, and synthetic fiber production.

Hydronium Ion (H3O+)

  • Hydrogen ions (H+) are extremely reactive and do not exist freely in water.
  • They react with water to form the hydronium ion (H3O+).
  • Reaction: H+ + H2O → H3O+

Definitions of Acids and Bases

  • Arrhenius Definition:
    • Acids produce H3O+ ions in water.
    • Bases produce OH– ions in water.
  • Brønsted-Lowry Definition:
    • Acids donate protons (H+).
    • Bases accept protons (H+).
  • Lewis Definition:
    • Acids are electron pair acceptors.
    • Bases are electron pair donors.

Arrhenius Theory

  • Acids release H+ in aqueous solution: HCl(aq) → H+(aq) + Cl−(aq)
  • Bases release OH− in aqueous solution: NaOH(aq) → Na+(aq) + OH−(aq)

Arrhenius Acid-Base Reactions

  • The reaction between an acid and base produces water and a salt.
  • For example: acid + base → salt + water, such as
    HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
  • Here, H+ from the acid reacts with OH− from the base.

Problems with Arrhenius Theory

  • It fails to explain why molecular substances like ammonia dissolve to form basic solutions (without OH– ions).
  • It does not account for how some ionic compounds create basic solutions without OH–.
  • It cannot explain why CO2 leads to acidic solutions without free H+.
  • It does not address acid-base reactions outside aqueous solutions.

Brønsted-Lowry Acid-Base Theory

  • Classifies acid-base reactions by proton transfer.
  • All reactions fitting the Arrhenius definition also fit this one.
  • Key Definitions:
    • Acids are H+ donors.
    • Bases are H+ acceptors.

Conjugate Acid-Base Pairs

  • In a Brønsted-Lowry reaction, each reactant and resulting product is a conjugate pair.
  • The acid becomes a conjugate base after donating a proton, and vice versa.

Acid Strength and Molecular Structure

  • The strength of binary acids depends on bond polarization and strength.
  • Trends:
    • Acidity increases across a period and down a column.
    • H—C < H—N < H—O < H—F
    • H—F < H—Cl < H—Br < H—I

Strengths of Oxyacids

  • Generally stronger than binary acids.
  • Strength is affected by the electronegativity of the nonmetal and the number of oxygen atoms bonded to it.