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General Chemistry: Buffers, Titrations, and Solubility Equilibria

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  • What is a buffer solution?
    A buffer is a solution that resists pH change when acids or bases are added, typically made of a weak acid and its conjugate base or a weak base and its conjugate acid.
  • What components make up a typical buffer?
    A buffer typically consists of (1) a weak acid and its conjugate base (salt), or (2) a weak base and its conjugate acid (salt).
  • How do buffers work according to Le Châtelier’s principle?
    Buffers neutralize added acid or base by shifting equilibrium: weak acid molecules react with added base, and conjugate base ions react with added acid to maintain pH.
  • Write the equilibrium reaction for acetic acid buffer system.
    CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq)
  • What is the Henderson–Hasselbalch equation?
    pH = pKa + log(\(\frac{[base]}{[acid]}\)), relates pH, pKa, and the ratio of conjugate base to acid concentrations in a buffer.
  • What is the effective pH range of a buffer?
    The effective pH range of a buffer is approximately pKa ± 1, where the buffer can effectively neutralize added acid or base.
  • What factors affect buffer effectiveness?
    Buffer effectiveness depends on (1) the relative amounts of buffer acid and base (ideally equal), and (2) the absolute concentrations of buffer acid and base.
  • How do you calculate pH of a buffer using an ICE table?
    Set initial concentrations, apply changes (x), and equilibrium expressions to solve for [H3O+], then calculate pH = -log[H3O+].
  • What happens to pH when strong acid or base is added to a buffer?
    Added acid reacts with conjugate base to form more acid; added base reacts with acid to form more conjugate base, causing only small pH changes.
  • Define titration and equivalence point.
    Titration is a technique to determine concentration by adding titrant to analyte; equivalence point is when stoichiometric amount of titrant is added.
  • What is a titration curve?
    A plot of pH versus volume of added titrant showing regions before, at, and after the equivalence point.
  • Describe the equivalence point pH for strong acid-strong base titrations.
    The equivalence point pH is neutral (pH = 7) because the salt formed is neutral.
  • What is the pH at the half-equivalence point in a weak acid titration?
    At half-equivalence point, pH = pKa of the weak acid.
  • How does the pH at equivalence point differ for weak acid-strong base titrations?
    The equivalence point pH is > 7 due to the basic nature of the conjugate base formed.
  • What is the common ion effect on solubility?
    The presence of a common ion decreases the solubility of an ionic compound by shifting equilibrium toward the solid.
  • How is the solubility product constant (Ksp) defined?
    Ksp is the equilibrium constant for the dissolution of a sparingly soluble ionic compound, expressed as the product of ion concentrations raised to their stoichiometric coefficients.
  • How to calculate molar solubility from Ksp for a salt MX?
    For MX ⇌ M+ + X-, Ksp = [M+][X-] = s^2, so molar solubility s = √Ksp.
  • What is selective precipitation?
    Selective precipitation separates ions by adding a reagent that precipitates one ion with the smallest Ksp first, requiring at least a 1000-fold difference in Ksp values.
  • What is a complex ion and its formation constant (Kf)?
    A complex ion contains a central metal cation surrounded by ligands; Kf is the equilibrium constant for its formation.
  • How does complex ion formation affect solubility?
    Formation of complex ions increases solubility of ionic compounds by removing free metal ions from solution.