Chemistry. It's not confined to a laboratory filled with test tubes, or a lecture at a university. Chemistry is the study of the world around us, of chemicals and how they interact. Everything is made of chemicals, from the pencils we write with to the oceans where we swim. We are made of chemicals. When we eat or breathe, chemical reactions take place inside us.

Many students have been amazed to realize that chemicals are, in fact, all around us. And, they are surprised that chemistry is a topic they can explore in their own classroom. To study chemistry is to make sense of the world. In a way, it's like solving a mystery.

In Chemical Tests, a 16-lesson unit designed for third-graders, students begin to use critical thinking skills to solve mysteries such as "What are the identities of five unknown solids?" By conducting a variety of physical and chemical tests, students explore some concepts basic to general chemistry: physical and chemical properties and how to describe them, and changes that may occur when different solids and liquids are mixed together or separated. As a result, students are introduced to solubility, filtration, evaporation, crystallization, and acids, bases, and neutrals. Along the way, they also develop essential skills: observing, recording, questioning, analyzing, and drawing conclusions.

At this age, many children increasingly can infer and predict on the basis of experiences, and they are beginning to support their conclusions both verbally and in written form. Using knowledge gained through observation and experimentation, third-graders also are starting to be able to solve the problems posed in this unit.

The unit begins with a pre-unit assessment lesson in which students share what they think about chemicals and what they would like to learn and gain from their first experience observing and describing an unknown material. In Lesson 2, students encounter the mystery of their five unknown solids (sugar, alum, talc, baking soda, and cornstarch), and assemble the tools they will use to gather the information necessary to solve it. They also practice observing and describing skills with known materials before moving on to unknowns in the next lesson.

In the next eight lessons, students perform a series of tests to help them determine some physical and chemical properties of their five unknown solids. In Lesson 3, students begin to investigate and record the physical properties of the five unknowns, first using their unaided senses, and then adding tools to extend and enhance their senses.

By adding water to the unknowns in Lessons 4 to 6, students learn that mixing one substance with another can reveal new properties. They also use filtration and evaporation to separate the combined substances and find that evaporation may lead to the formation of crystals.

By adding vinegar, iodine, and red cabbage juice to the unknowns in Lessons 7 to 9, the class continues to investigate the properties of the solids. By performing these different tests, students discover that mixing one substance with another can produce physical and chemical changes in form, color, odor, or texture. In their final chemical test on the unknown solids in Lesson 10, students observe that adding heat also can produce notable changes.

In Lesson 11, students review, analyze, and discuss the information they have collected to help identify the five unknown solids. In the next lesson, students compare this information to a Chemical Information Sheet, a reliable source of outside data, to discover the unknowns' identities at last. A reading selection illustrates the important role these and other chemicals play in students' everyday lives. Then, in Lesson 13, students articulate the process they have used to solve their mystery and apply their testing, observing, recording, and analyzing skills to a new situation.

Lesson 14 challenges students to go a step beyond identifying one unknown solid as they perform a chemical analysis on a mixture of two unknown solids. Next, students use the red cabbage juice test and a reading selection to learn about three important chemical groups: acids, bases, and neutrals. Students then apply their new knowledge to the five solids they investigated earlier.

Finally, Lesson 16 is an embedded assessment of the skills students have been developing throughout the unit. Here, students face a challenging reversal: instead of using known test liquids (water, vinegar, iodine, and red cabbage juice) to identify an unknown solid, they use the properties of their five original solids (sugar, alum, baking soda, talc, and cornstarch) to identify one of the test liquids.

As students become more aware of the chemicals in their world, they are likely to have a number of questions that cannot easily be answered. It is a good idea to remind them that our knowledge of chemistry is always growing and changing. What you can do is help students learn how to continue to find out for themselves.