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Online Chemistry Labs | Learning Objectives

Background:

This experiment allows the student to study in depth the aqueous equilibria involving a weak acid, its conjugate base, and the buffer formed by combining them. A portable pH meter can be moved from flask to flask to monitor the pH of solutions. After investigating the response of boiled deionized water to the addition of a small measured amount of strong base, the student prepares in turn solutions of known concentration weak acid, conjugate base, and buffer. Each one is subjected to dilution with water and to the addition of a small amount of strong base. The meaning of "buffer capacity" is introduced. The student measures the buffer capacity of the buffer solution and also calculates what the capacity is expected to be from the composition. The student must select the correct generic ionic equilibrium that describes what is occurring in each solution as changes are made.

 Weak Acid Equilibria

Learning Objectives:

  1. Study the equilibria involving a weak acid, its conjugate base, and their buffer using a pH meter to monitor the situation.
  2. Be able to perform a series of solution preparations, reagent additions, and measurements.
  3. Be able to select the best symbolic ionic reaction to describe the equilibria involved and account for the observed shifts in pH when additional reagents are added.
  4. Be able to calculate the observed buffer capacity of a solution and compare that value to the capacity expected to result from the buffer composition.
  5. Be able to compute the expected pH of various buffer solutions using the Henderson-Hasselbalch equation.