chapter10-students

Chapter 10: Reactions in Aqueous Solutions I: Acids, Bases & Salts

Chapter Goals

  • Understand the properties of aqueous solutions of acids and bases.

  • Study key theories:

    • Arrhenius Theory

    • Hydronium Ion (H3O+)

    • BrØnsted-Lowry Theory

    • Autoionization of Water

    • Amphoterism

    • Strengths of Acids

  • Learn about:

    • Acid-Base Reactions in Aqueous Solutions

    • Acidic Salts and Basic Salts

    • Lewis Theory

Properties of Aqueous Solutions of Acids and Bases

Acidic Solution Properties

  • Taste: Sour

  • Indicator Changes:

    • Blue litmus to red

    • Bromothymol blue: blue to yellow

  • Reactivity:

    • Reacts with metals to generate H2(g)

    • Reacts with metal oxides and hydroxides to form salts and water

    • Conducts electricity

Basic Solution Properties

  • Taste: Bitter

  • Feel: Slippery

  • Indicator Changes:

    • Red litmus to blue

    • Bromothymol blue: yellow to blue

  • Reactivity:

    • Reacts with acids to form salts and water

    • Conducts electricity

The Arrhenius Theory

  • Proposed by Svante Arrhenius in 1884.

  • Acids: Produce H+ in aqueous solutions.

    • Examples: HCl, H2SO4

  • Bases: Produce OH- in aqueous solutions.

    • Examples: NaOH, KOH

  • Neutralization Reactions: Formation of water from H+ and OH-.

  • Strong Acids: Ionize 100% in water.

    • Examples include HCl, HNO3, H2SO4.

  • Strong Bases: Ionize 100% in water.

    • Examples include NaOH, Ca(OH)2.

The Hydronium Ion (H3O+)

  • Protons generated are not free but hydrated.

  • H3O+ is the representation of the hydrated hydrogen ion.

The BrØnsted-Lowry Theory

  • Developed by J.N. BrØnsted and T.M. Lowry in 1923.

  • Acid: Proton donor (H+).

  • Base: Proton acceptor.

  • Conjugate Acid-Base Pairs: Two species that differ by one proton.

  • Example Reaction: HNO3 + H2O → H3O+ + NO3-.

Amphoterism

  • Species that can act as both acids and bases are called amphoteric.

  • Proton transfer reactions where a species behaves as either an acid or base are termed amphiprotic.

Strengths of Acids

  • Binary Acids: Strength increases with decreasing bond strength H-X.

  • Hydrohalic Acids: HF > HCl > HBr > HI for bond strength, HF < HCl < HBr < HI for acid strength.

  • Ternary Acids: Strength increases with:

    • Increasing number of O atoms on the central atom.

    • Higher oxidation states of the central atom.

  • The strongest acid in water is H3O+; stronger acids react with water.

Acid-Base Reactions in Aqueous Solutions

  • Four types of acid-base reactions:

    1. Strong acids - strong bases

    2. Weak acids - strong bases

    3. Strong acids - weak bases

    4. Weak acids - weak bases

Examples of Acid-Base Reactions

  1. Strong Acid + Strong Base:

    • Example: HBr + Ca(OH)2 → CaBr2 + 2H2O.

    • Total Ionic: 2H+ + 2Br- + Ca2+ + 2OH- → Ca2+ + 2Br- + 2H2O.

    • Net Ionic: H+ + OH- → H2O.

  2. Weak Acid + Strong Base:

    • Example: HNO2 + NaOH → NaNO2 + H2O.

    • Total Ionic: HNO2 + Na+ + OH- → Na+ + NO2- + H2O.

    • Net Ionic: HNO2 + OH- → NO2- + H2O.

  3. Strong Acid + Weak Base:

    • Example: HNO3 + NH3 → NH4NO3.

    • Total Ionic: H+ + NO3- + NH3 → NH4+ + NO3-.

    • Net Ionic: H+ + NH3 → NH4+.

  4. Weak Acid + Weak Base:

    • Example: CH3COOH + NH3 → NH4CH3COO.

    • Total Ionic: CH3COOH + NH3 → NH4+ + CH3COO-.

    • Net Ionic: CH3COOH + NH3 → NH4+ + CH3COO-.

Acidic and Basic Salts

  • Acidic Salts: Formed by polyprotic acids reacting with a limited amount of base.

    • Example: H2SO4 + NaOH → NaHSO4 + H2O.

  • Basic Salts: Formed by polyhydroxy bases reacting with limited amounts of acid.

    • Example: Ba(OH)2 + HCl → Ba(OH)Cl + H2O.

  • Both types can neutralize acids and bases but result in solutions that are acidic or basic depending on the salt formed.

The Lewis Theory

  • Developed by G.N. Lewis in 1923, emphasizes electron interactions.

  • Acids: Electron pair acceptors.

  • Bases: Electron pair donors.

  • Example: NH3 donates an electron to HBr in ionization.

  • Example: NaF + BF3 → Na+ + BF4- (only a Lewis interaction).

Summary of Acid-Base Theories

  • Arrhenius, Brønsted-Lowry, and Lewis theories complement each other in understanding acid-base reactions.