Chapter 18: Aqueous Ionic Equilibria

Recognize that all equilibrium problems are solved in fundamentally the same manner using ICE tables.

*Know the material covered in Chemistry I on solubility (see sections 9.4-9.6)

DEFINE:

• Buffer
• Common ion effect
• Complex ion and ligand
• Selective precipitation
• Unsaturated, saturated and supersaturated solutions (review)
• Main characteristics of an effective buffer.

DO:

• State when it is appropriate to use the Henderson-Hasselbalch equation to calculate the pH (of a buffer ONLY)
• Explain the limits of buffering capacity of a buffer solution given the stoichiometric consumption of the weak acid or conjugate base
• Explain how you would make a buffer solution from a weak base and its conjugate acid and calculate the pH of such a buffer solution
• Select an appropriate indicator from a list for a specific titration.  Explain why indicators are not “one size fits all”
• Write equilibrium expressions for the dissolution of ionic compounds into their constituent ions, aka “solubility products” (K_sp)
• Discuss the role of pH plays in solubility equilibria
• Predict whether or not precipitation will occur by comparing Q_sp to K_sp
• Choose conditions permitting selective precipitation for a given situation
• Write equilibrium expressions for the formation of complex ions from metal cations and neutral or anionic ligands, aka “formation constants” (K_f)
• Describe the effect of complex ion formation on solubility of metal ions

CALCULATE:

• The pH of a buffer solution from the pK_a or Ka and the initial concentrations of a weak acid and conjugate base
• Recognize that a solution containing a weak acid and its conjugate base is a buffer, and, given intital concentrations and K_a values, calculate the pH
• Calculate the change in pH of a buffer solution upon addition of a small amount of strong acid or strong base
• Use pK_a to choose an appropriate conjugate acid-base pair to make a buffer solution for a specific situation
• Calculate solubility of ionic compounds in pure water and in solutions containing a common ion using K_sp and an ICE table

For the following titrations - strong acid (base) with a strong base (acid), weak acid (base) with a strong base (acid) or a polyprotic acid with a strong base:

A. Calculate the pH at any point along the titration curve

B. Sketch titration curve and mark the equivalence point(s) and buffer region(s) on the curve

C. Define the equivalence point(s) (recognize the value can be determined using a pH meter)

D. Define the half equivalence point(s);  State the significance of this point

E. Define endpoint of the titration;  Explain why this is an approximation of the equivalence point

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