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 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.

Acid-base chemistry is a common topic in a introductory chemistry course. Such a unit often begins with a discussion of the observable properties that make and acid different than a base. Distinguishing acids from bases based on observable properties is the focus of this Concept Builder. There are three levels of difficulty in the Concept Builder. In the first level of difficulty (Apprentice Level), students must recognize an acid or a base on the basis of its pH value, a litmus test, and the label on a lab bottle. In the second level of difficulty (Master Level), students must be able to do everything from the Apprentice Level and additionally relate the following to acid-base identity: the relative pH-pOH values, the hydronium ion concentration, the results of a phenolphthalein test, the chemical property of acids reacting with metals, and the physical property of bases feeling slippery. And finally in the third level of difficulty (Wizard Level), students must be able to do everything from the previous levels and additionally be able to relate the following to acid-base identity: the hydroxide ion concentration, the color of pH paper, and the sour taste of acids.

The Concept Builder is modeled after a popular children's exercise that goes like ... "One of these things is not like the other. Which one doesn't belong?" In the Concept Builder, there might be four statements given. Three of the statements are characteristic of acids and the fourth is not. Students must determine which one of the four does not belong; that is, which one is not like the other ones.

The three difficulty levels are differentiated as follows:
 

• Apprentice Difficulty Level: Question Groups 1-4 ... Each question includes three acid-base property statements. 
• Master Difficulty Level: Question Groups 1-8 ... Each question includes either three or four acid-base property statements. Four of the Question Groups in this difficulty level are the four Groups from the Apprentice Difficulty Level.
• Wizard Difficulty Level: Question Groups 5-12 ... Each question includes four or five acid-base property statements. Four of the Question Groups are from the Master Difficulty Level.

To provide a complete experience without any redundancy, teachers should assign the Apprentice and the Wizard Difficulty Levels. 

Like all our Concept Builders, this Concept Builder utilizes a variety of strategies to make each student's experience different. The ordering of questions is random. The Question number assigned to each question is scrambled. For instance, two side-by-side students will not have the same question for question number three. And questions are organized into "groups" with questions within the same group being very similar (for instance, they have the same type of representations) but not identical.

The Concept Builder also keeps track of student progress. It requires that students demonstrate a mastery of questions in each Question Group. If they miss a question from one group, then they will have to answer two consecutive questions correctly in order to demonstrate mastery. Progress is displayed in the progress report on the right side of the Concept Builder. A star indicates a demonstration of mastery. A question with a red background indicates that the student has missed the question. And a question with a yellow background means that the student must get one more question from that Question Group correctly answered in order to obtain a star. When an activity is completed, the student will be awarded a Trophy. This Trophy is displayed on the Main Menu screen. These strategies make the Concept Builder an ideal addition to the 1:1 classroom and other settings in which computers are readily available. 


In order to complete an activity, a student must correctly analyze each question of that difficulty level. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through an activity, a system of stars and other indicators are used to indicate progress on the activity. A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the que of questions to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question of a difficulty level has been analyzed, the student earns a Trophy which is displayed on the Main Menu. This system of stars and trophies allows a teacher to easily check-off student progress or offer credit for completing assigned difficulty levels.

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.