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.