### Notes:

The Density Ranking Tasks Concept Builder is an adjustable-size file that displays nicely on smart phones, on tablets such as the iPad, on Chromebooks, and on laptops and desktops. The size of the Concept Builder can be scaled to fit the device that it is displayed on. The compatibility with smart phones, iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom.

### Teaching Ideas and Suggestions:

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.

Most Chemistry courses begin with a discussion of matter and the physical and chemical properties which allow one to distinguish between different samples of matter. One of those identifying properties is density - the mass per volume ratio. This Concept Builders focuses on the concept and the mathematics of density. Each of the 15 Question Groups presents information to the learner that allows them to rank three samples of matter according to their relative density. In most cases, the information is very conceptually-oriented. Rather than provide numerical values, the mass and volume information is provided in the form of particle diagrams, the location where a sample of shredded matter would settle in a density column, or the amount of mass required to displace a fixed amount of water (or the amount of water displaced by a fixed mass). In every question, students must use their conception of density in order to make judgements about which sample has the greatest, the smallest or the middlest amount of density.

There are activities in the Concept Builder. Those three activities can be described as follows:

• Particle Diagrams: Question Groups 1-6 ... Analyze particle diagrams for three samples of matter in order to rank them according to their density..
• Mass and Volume: Question Groups 7-9 ...Rank three samples of matter according to their density based upon information about their mass and volume values.
• Sink, Float and Displace: Question Groups 10-15 ... Make observations about density columns and density experiments in order to rank three samples of matter according to heir density..

The questions from each group are shown on a separate page. Teachers are encouraged to view the questions in order to judge which activities are most appropriate for their classes.

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 information as "givens") but not identical. And finally, the answer options are always scrambled.

In order to complete an activity, a student must correctly analyze each question of that activity. 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 an activity 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 activities.

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.