We're going to be honest: we do Physics. That's why this is called The Physics Classroom website. And when we do the Teacher's Notes section for our Concept Builders, we typically have a lot to say ... and a lot of resources to point you to. We're not claiming to be ignorant of chemistry; we just don't have a lot of chemistry resources here at The Physics Classroom to point you to. And so this page is going to be a lot shorter than our usual page that accompanies our Physics Concept Builders. That's our honest confession.
A typical objective in most chemistry courses is to be able to relate the hydronium and hydroxide ion concentration to the pH and the pOH value. This objective is the purpose of this Concept Builder. The activity consists of three scaffolded difficulty levels, each of which involves the completion of a table. The table contains columns like pH, pOH, [H
3O
+], and [OH
-]. The table has several incompleted cells and students must use their understanding of the topic to complete the table cells.
Each difficulty level has four different tables. The tables are randomly selected such that different students will have different tables. The
Apprentice Difficulty Level, students must relate the pH value to the pOH value and the acidity or basicity of the solution. In the
Master Difficulty Level, and additional variable is added - the hydronium ion concentration. And then in the
Wizard Difficulty Level, students must also incorporate understanding of the hydroxide ion concentration.
We recommend that students use three significant digits in their answers, especially the concentration values. The answer checking algorithm makes sure that the student inputted answer is within 1% of the keyed answer (known to 16 digits). Using three significant answers may be a deparature from the rules of significant digits but it avoids errors owed to rounding.
Teachers using the Concept Builder with their classes should preview the activity (or view the
Questions in a separate file) in order to judge which levels would be most appropriate for their students.
Students can complete as much of the table as they wish before checking their answers. And they can check their answers as many times as they wish. Feedback regarding the correctness of their answers is immediate and provided using a color-coding system. Correct answers are displayed in a table cell with a green background; these correct answers become
locked and cannot be changed. Incorrect answers are displayed in a table cell with a red background. Each time students check their answers, the number of missed answers is determined. A running tally is kept of the number of misses. When a student accurately completes the table, a Health rating is displayed on the screen. The Health rating is dependent upon the number of misses. Formulas for computing the Health rating are discussed
on a separate page. The Health rating is also displayed on the Main Menu screen for any completed difficulty level. A student can always repeat a difficulty level in order to improve their Health rating for that level. The best Health rating is always displayed on the Main Menu screen below the trophy for that difficulty level.
We leave it to the discretion of individual teachers as to what they wish to do with the Health rating information. We recognize that there will be some teachers who feel most comfortable with their students in simply requiring that a difficulty level be completed and trophy be earned. Other teachers may wish to require completion of a difficulty level with a minimum Health rating. For instance, such teachers may require that each difficulty level be completed with a 70% or higher Health rating. Still other teachers may tie the Health rating into a grade or allow a homework pass for completing an activity that exceeds a 90% Health rating. Decisions as to what to do with the Health rating are best left for individual teachers who know their students the best.
The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise.