General Chemistry Acid-Base Titrations

  • Common Ion Effect

    • Suppresses ionization of a weak acid/base due to presence of a common ion from a strong electrolyte

  • Buffer Solution: Weak Acid & Conjugate Base | Weak Base & Conjugate Acid (Adding strong acid takes up conjugate base and produces more weak acid and the reverse as well for adding strong base)

    • Buffers are solutions that can resist changes in pH
    • When [HA] = [HA-] which is a perfect buffer, the pH = pKa
    • Reaction of added acid/base with buffer is stoichiometric
    • Buffer Range: pH = pKa +/- 1.0
    • To make buffer with a specific pH, pick a weak acid with it’s pKa closest to the desired pH

    Henderson-Hasselbalch Equation: pH = pKa + log10(A-/HA)*can use moles or M since it’s a ratio \n

  • Acid Base Titrations

    • Equivalence point (EP): The point in an acid-base titration where the moles of base = moles of acid
    • Strong Acid/Strong Base: Can ignore salt in calculation since it doesn’t affect pH, at EP pH = 7.00 and is neutral.
    • Weak Acid/Strong Base: Creates a buffer, can use H-H equation, at ½ EP the pH=pKa, at EP pH > 7 and will be basic from the weak conjugate base (products side), effect of weak conjugate base in solution becomes insignificant if there’s other things in solution
    • Strong Base/Strong Acid: Ignore salt as it has no effect on pH, at EP pH = 7.00 and is neutral
    • Weak Base/Strong Acid: Creates a buffer, can use H-H equation, at ½ EP the pOH=pKb, at EP pH < 7.00 from effect of the weak conjugate acid, effect of weak conjugate acid in solution becomes insignificant if there’s other things in solution

  • Where you are in titration (monoprotic & monobasic)

    • Mols in Beaker > Mols Titrant; Before Equivalence Point
    • Mols in Beaker < Mols Titrant; After Equivalence Point
    • Mols in Beaker = Mols Titrant; At Equivalence point

Solubility Equilibrium

  • Ksp is the equilibrium constant for a solid substance dissolving in an aqueous solution

ex. AgCl(s) → Ag + Cl

Ksp = [Ag][Cl]

*solids always on the left and not included in the Ksp

*remember stoichiometric coefficients

*molar solubility (mols) and solubility (grams) can be converted through solid’s molar mass (molar solubility = X)

*larger Ksp = more soluble compounds

  • Qsp is the solubility product for a reaction NOT at equilibrium

Qsp > Ksp; Precipitation forms; PPTs until Q=K

Qsp < Ksp; No Precipitation (unsaturated)

Qsp < Ksp; No Precipitation (saturated)

  • Factors Affecting Solubility
    • Common Ion Effect: Adding common ion lowers solubility, shifts reaction to the left (Treat as though you are removing/adding a reactant/product and estimate the shift of the reaction)
    • pH
    • Increase pH (add OH- ions) = Shift to the left = Less soluble
    • Lower pH (add H+ ions) = Shift to the right = More soluble