Ichem_imc_ws2024_chapter_10-12

Chapter Overview

  • CHAPTER 10: ACID-BASE EQUILIBRIA

    • Context: General and Inorganic Chemistry Theory at University of Applied Sciences Krems.

Definitions and Theories

  • Traditional definitions of acids and bases often based on taste (not recommended).

  • Arrhenius Theory:

    • Acid: Substance that produces hydronium ions (H3O+) when dissolved in water.

    • Base: Substance that produces hydroxide ions (OH-) in water.

    • Genius: Svante Arrhenius, Nobel Prize in Chemistry (1903).

  • Brønsted Theory:

    • Acid-base reaction as a proton transfer reaction (H+).

    • Does not require water for reactions.

Acid-Base Reactions

  • Acid reacts with water:

    • HA + H2O ⇄ A- + H3O+

  • Base reacts with water:

    • B + H2O ⇄ BH+ + OH-

  • Important definitions:

    • Acid: Proton donor.

    • Base: Proton acceptor.

    • Conjugated pairs: Strong acid has a weak conjugated base.

    • Strong base has a weak conjugated acid.

Examples of Reactions

  • Example: HSO4- + PO4³- ⇄ SO4²- + HPO4²-

    • Acid: HSO4- ; Base: PO4³-

Important Acids to Know

  • Hydrochloric acid (HCl), hydrosulfuric acid (H2S), hydrofluoric acid (HF), hydrobromic acid (HBr).

  • Oxoacids: Contain oxygen, hydrogen, and another element.

    • For example: H2SO4 (sulfuric acid), HNO3 (nitric acid), H2CO3 (carbonic acid), H3PO4 (phosphoric acid).

  • Formation of Oxoacids: Nonmetal oxides react with water:

    • SO3 + H2O ⇄ H2SO4

    • CO2 + H2O ⇄ H2CO3.

      (=acetic anhydrides)

      H2SO4 (sulfuric acid), H2SO3 (sulfurous acid), HNO3 (nitric acid), HNO2 (nitrous acid)

Properties of Acids and Bases

  • Polyprotic Acids: Donate more than one proton; e.g., diprotic (H2SO4), triprotic (H3PO4).

  • Halogen Oxoacids: Named by oxygen content; e.g., hypochlorous acid (HClO), perchloric acid (HClO4).

Organic Acids

  • Characterized by carboxyl group (R-COOH).

  • Examples:

    • Formic acid (HCOOH), acetic acid (CH3COOH), HOOC-COOH (oxalic acid), citric acid.

Bases

  • Strong bases: Soluble metal hydroxides (IA and IIA metals).

    • Examples: LiOH (Lithium hydroxide), NaOH (Sodium hydroxide), KOH (potassium hydroxide) , Ca(OH)2, Sr(OH)2, Ba(OH)2.

Ampholytes

  • Compounds that can act as both acids and bases (e.g., H2O, NH3).

  • At least a negative charge or one lone electron pair (to accept the proton)

Acid Strength Measurement

  • Acid strength judged by proton donation (H2O as a base).

  • Equilibrium constant K_A indicates strength of dissociation:

    • K_A = [A-][H3O+]/[HA].

    • K_A….acid dissociation constant

    • High K_A values when strong acids completely dissociates into the anion and proton

    • The ion product of water K_W= 10^-14 (weak ability to be a current)

    • Weak acids: All substances with a lower K_A than water (10^-14) are not treated as acids

    • Base has a K_B value (same principle)

pH Measurement

  • pH Equation: pH = -log[H3O+].

  • pOH Equation: pOH = -log[OH-].

  • Connection: pH + pOH = 14.

  • pH values smaller than 7= ACIDIC, pH values greater than 7= BASIC

  • pH value=7 (NEUTRAL-water)

  • pH can be determined by setting the concentration of the compound equal to H3O/OH formed and their concentration in the solution.

  • Acid and Bases are not needed in a 1:1 ratio

  • pK_A + pK_B = 14

  • To switch between K_A and pKA, the following formula is used: pKA= -logKA

    and KA= 10^-pKA

  • Formula for weak acids where only a small part of the substance dissociates: pH=1/2(pKA-log©)

Buffer Systems

  • Buffers resist changes in pH upon adding acids or bases.

  • Composed of a weak acid and its salt.

  • Buffer equation: pH = pKa + log[A-]/[HA].

  • Buffer capacity: how much string acid/base is needed to change the pH of a buffer solution

Titration and Calculating Reaction Rates

  • Titration used to determine concentration.

  • Equivalence point: Reaction where amounts of acid/base are stoichiometrically equal.

Key Takeaways for Exam Preparation

  • Understand the definitions of acids and bases according to different theories.

  • Familiarize with key reactions, examples, and equations.

  • Practice calculating pH, pOH, and buffer concentrations.