Making Acids and Bases MORE Basic: Supporting Students’ Conceptualization of Acid–Base Chemistry through a Laboratory Exercise That Connects Molecular-Level Representations to Symbolic Representations and Experimentally Derived Evidence

Abstract

Acid–base chemistry is an important and challenging topic for virtually all chemistry students. Recent works have focused on conceptually linking molecular and symbolic representations to experimental evidence for many chemical concepts. In this work we describe a laboratory exercise designed to address students’ conceptual challenges regarding acid–base chemistry, particularly with respect to organic acids, titrations, and pK a’s. This work is part of a series of laboratory exercises developed for prehealth students using the MORE (model, observe, reflect, explain) pedagogy. In this lab, students titrated an amino acid with sodium hydroxide according to lab procedures typically used in a prehealth lab. Our work differs from traditional laboratories in the emphasis on connecting molecular-level representations to symbolic representations and experimentally derived evidence. Using this course environment, we sought to understand the ways in which students’ understandings (molecular-level, symbolic, or evidential) are coconstructed or discrete. We further sought to guide students toward connecting these understandings and report on our successes and areas for improvement.

Inquiry-Based Laboratories for Students to Investigate the Concepts of Acid–Base Titration, pKa, Equivalence Points, and Molar Absorption Coefficients

“…Many techniques, such as the first-derivative plot, the second-derivative plot, and Gran’s plot, were employed in previous studies to identify the equivalence point of the titration. , These methods have drawbacks when the compounds have more than one proton dissociation constant ( K a ), particularly at higher p K a values, where it is difficult to determine the true equivalency point. ,, Therefore, we used an alternative technique called the mole fraction species plot to identify the accurate equivalence point. The p K a from Part 1 and the proton concentration from Part 2 were used to calculate the mole fraction species of each species according to the equation F false[ normalH italicn normalA false] = false[ normalH italicn normalA false] false[ normalH 3 normalA false] + false[ normalH 2 normalA − false] + false[ normalHA 2 − false] + false[ normalA 3 − false] . , …”

“…Many techniques, such as the first-derivative plot, the second-derivative plot, and Gran’s plot, were employed in previous studies to identify the equivalence point of the titration. , These methods have drawbacks when the compounds have more than one proton dissociation constant ( K a ), particularly at higher p K a values, where it is difficult to determine the true equivalency point. ,, Therefore, we used an alternative technique called the mole fraction species plot to identify the accurate equivalence point. The p K a from Part 1 and the proton concentration from Part 2 were used to calculate the mole fraction species of each species according to the equation . , …”

Student-Generated Videos to Promote Understanding of Chemical Reactions

“…This concept is frequently represented with a triangle (Johnstone’s triangle) with the three apexes labeled with the macroscopic, submicroscopic, and symbolic terms. The model is also known as the chemistry triplet and has been widely used as the conceptual foundation for countless investigations in the field of chemical education. − The holistic Johnstone’s model shows its utility as a framework that allows students to establish relationships between the different components of its triangle. This continuous switch between the three levels is a sort of “mental gymnastics” which gives the student an overall view of the complex nature of chemistry.…”

Calculating the pH of a Strong Acid or a Strong Base Before and After Instruction in General and Analytical Chemistry

“…From previous investigations, we have developed an awareness of student reasoning about acid–base reactions, common misconceptions involving acid–base concepts, strategies for calculating pH, − and student conceptual understanding of logarithms and pH. , These studies indicate students often have a surface-level understanding of these topics. For example, students struggle to understand what the strength of an acid or a base means, what pH means, and what takes place during an acid–base reaction. , Additionally, students have difficulty writing acid–base chemical equations and struggle to make sense of the molecular, symbolic, and macroscopic representations of acids and bases and connecting the concept of pH to the chemistry occurring in an actual solution . We have come to understand the complexity of the topic of acids and bases, and the fact that it remains challenging for many students indicates that important work remains to be done.…”

“…For example, students struggle to understand what the strength of an acid or a base means, what pH means, and what takes place during an acid−base reaction. 15,16 Additionally, students have difficulty writing acid−base chemical equations 17 and struggle to make sense of the molecular, symbolic, and macroscopic representations of acids and bases 18 and connecting the concept of pH to the chemistry occurring in an actual solution. 19 We have come to understand the complexity of the topic of acids and bases, and the fact that it remains challenging for many students indicates that important work remains to be done.…”