Chapter 17: Acids and Bases

Characteristics of Acids & Bases

  • Characteristics of Acids:

    • Sour taste (e.g., lemon juice, vinegar)
    • Ability to dissolve metals
    • Turns blue litmus paper red
    • Neutralizes bases

  • Characteristics of Bases:

    • Bitter taste (e.g., in poisons like hemlock)
    • Slippery feel (used to make soaps!)
    • Turns red litmus paper blue
    • Neutralizes acids
Common Acids

  • Hydrochloric acid (HCl):

    • Uses: Metal cleaning, food preparation, ore refining, stomach acid

  • Sulfuric acid (H₂SO₄):

    • Uses: Fertilizer & explosives manufacturing, dye & glue production, in batteries

  • Nitric acid (HNO₃):

    • Uses: Fertilizer & explosives manufacturing, dye & glue production

  • Acetic acid (HC₂H₃O₂):

    • Uses: Food preservation, rubber manufacturing, active component of vinegar

  • Citric acid (H₃C₆H₅O₇):

    • Occurrence: Found in citrus fruits, adjusts pH in foods/beverages

  • Carbonic acid (H₂CO₃):

    • Occurrence: Forms in carbonated beverages

  • Hydrofluoric acid (HF):

    • Uses: Metal cleaning, glass frosting & etching

  • Phosphoric acid (H₃PO₄):

    • Uses: Fertilizer manufacturing, biological buffering, beverage preservation
Common Bases

  • Sodium hydroxide (NaOH):

    • Uses: Petroleum processing, soap & plastic manufacturing

  • Potassium hydroxide (KOH):

    • Uses: Cotton processing, electroplating

  • Sodium bicarbonate (NaHCO₃):

    • Uses: Baking soda, antacid

  • Sodium carbonate (Na₂CO₃):

    • Uses: Glass & soap manufacturing

  • Ammonia (NH₃):

    • Uses: Detergent, fertilizer manufacturing
Acid-Base Definitions

  • Arrhenius Definition:

    • Acids produce H⁺ ions in H₂O.
    • Bases produce OH⁻ ions in H₂O.
    • Acids and bases combine:
      H+(aq)+OH−(aq)→H2O(l)H^+ (aq) + OH^- (aq) → H₂O (l)

  • Brønsted-Lowry Model:

    • Acids are H⁺ donors; bases are H⁺ acceptors.
    • Example:
      H2SO4(aq)+H2O(l)⇌HSO4−(aq)+H3O+(aq)H₂SO₄ (aq) + H₂O (l) ⇌ HSO₄^- (aq) + H₃O^+ (aq)
Conjugate Acid-Base Pairs
  • A Brønsted-Lowry acid donating an H⁺ forms its conjugate base.
  • A Brønsted-Lowry base accepting a proton becomes a conjugate acid.
  • Example:
    • NH3(base)⇌NH4+(conjugateacid)NH₃ (base) ⇌ NH₄^+ (conjugate acid)
  • Pairs differ only by the presence/absence of a proton.
Relative Strengths of Acids and Bases
  • Strength indicates the degree of ionization (K values).
  • Strong acids: (fully ionized)
    • Examples: HCl, HBr, HI, HNO₃, H₂SO₄, HCIO₄
  • Weak acids: (partially ionized)
    • Examples: Acetic acid (HC₂H₃O₂), HF, H₃PO₄
The pH Scale
  • pH Calculation:
    pH=−extlog[H+]pH = - ext{log}[H^+]
    pOH=−extlog[OH−]pOH = - ext{log}[OH^-]
    pKw=pH+pOH=14pK_w = pH + pOH = 14
Water's Autoionization
  • H2O(l)+H2O(l)⇌H3O+(aq)+OH−(aq)H₂O (l) + H₂O (l) ⇌ H₃O^+ (aq) + OH^- (aq)
  • For neutral water: [H3O+]=[OH−]=1.00imes10−7M[H₃O^+] = [OH^-] = 1.00 imes 10^{-7} M
    • Kw = [H+][OH−]=1.00imes10−14[H^+][OH^-] = 1.00 imes 10^{-14}
Acid-Base Calculations
  • To find pH of a strong acid solution (e.g., 0.0500MextHCl0.0500 M ext{HCl}):
    • Calculate pH, pOH, and [OH−][OH^-].
Weak Acids & Bases
  • Weak acid example:
    • HNO2+H2O⇌H3O++NO2−HNO₂ + H₂O ⇌ H₃O^+ + NO₂^-
  • The ionization equation applies.
  • Weak base example (NH₃):
    • NH3+H2O⇌NH4++OH−NH₃ + H₂O ⇌ NH₄^+ + OH^-
Polyprotic Acids
  • Polyprotic acids can donate multiple protons (e.g., carbonic acid).
    • Each step has smaller K values.
Salt Solutions
  • Hydrolysis: Dismantling salts in water.
    • Cation from a weak base creates H₃O⁺; anion from a weak acid creates OH⁻.
Lewis Acids and Bases
  • Lewis Base: Donates an electron pair.
  • Lewis Acid: Accepts an electron pair.
  • Examples include ions with lone pairs or incomplete octets.