Do you have a favorite acid-base titration lab?

HCl and NaOH, a strong acid - strong base titration? Citric acid and NaOH, a weak, triprotic acid - strong base titration? Do your students standardize the NaOH solution as a first step?

As a second year AP teacher, I am full of questions about acid-base chemistry pedagogy. College Board's AP Insight program lays out guided inquiry activities to address this core "challenge area." The activities build students' conceptual understandings of the following topics:

  • Strong acids
  • Bronsted-Lowry theory
  • Weak acid and weak base net ionic equations
  • Significance of strong conjugate acids and strong conjugate bases producing additional H+ and OH-
  • pH and pOH calculations
  • Dissociation equations and ICE charts for weak acids and bases
  • Neutralization equations and ICL charts for strong acids and bases
  • Titrations curves (equivalence points, half-equivalence points, buffering regions)
  • Bond strengths and understanding acid-base strength
  • How buffers work
  • Setting up a buffer

These performance tasks have helped me tremendously this year, and I am feeling more confident about my students' conceptual knowledge.

However, the AP exam seems to regularly ask a free response question about titration. Like everyone else, we are pushed for time. Some veteran AP teachers suggest using a virtual lab, some suggest doing a demonstration, others suggest a full standardization of NaOH with a strong acid titration, and still others have encouraged a weak acid titration as they believe buffer systems are only understood when experienced. Can my students be successful if we don't titrate a weak acid? Can my students adequately answer the free response question if I wait to titrate in lab until after the exam? What is your opinion? I can't be the only new AP teacher wondering, right? 

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Comments 2

David Frohnapfel's picture
David Frohnapfel | Wed, 10/17/2018 - 11:35

We recently revised our first semester lab curriculum to focus on quantitative laboratory techniques. The nice thing about titrations is that they can be used to emphasize all key aspects of solution preparation, solution transfer, and solution analysis.  Students also gain valuable experience working with concentration values rather than mass to determine moles and this has great advantages with other types of experiments and stoichiometry calculations. 

Our current series includes calibration activities for vol. pipets and burets and a qualitative volumetric flask activity to prepare them to titration. We then standardize NaOH and use this solution to titrate household vinegar.  We follow up with an analysis of a sulfuric acid solution where the students have to quantitatively dilute the solution prior to titrimetric analysis. 

The students become quite adept at the basic procedures and these skills carry to the second semester where we perform 4 additional titrations including 2 additional acid-base (solubility of Ca(OH)2 and analysis of Ni(NH3)6Cl2 product), redox (vitamin C determination) and complexometric (water hardness via EDTA). We also have them determine a titration curve for a weak acid using Hanna pH checkers. It seems like a lot of titration, but the student's facility with the basic procedures allows them to better focus on the chemistry of the different experiments in the second semester. They are also doing much better in the upper level analytical chemistry course since we revised the curriculum.