Testing Unknown Solids with Vinegar

In this lesson, students begin to examine the unknowns chemical properties. A chemical property of a substance is its ability to transform into new materials. We can observe chemical properties when substances react with one another. For example, when iron is exposed to moist air, a new substance (rust) may form. So, the ability to rust is a chemical property of iron. The ability to burn is a chemical property of wood and cotton. 

In Lesson 5. students compared how plain water looked before and after they had added the unknown. Although they may not have been aware of it at the time, students were using the water as a control—an unchanged basis of comparison— to make these observations. In this lesson, students are formally introduced to the concept of a control when they use the unlabeled circle on their test mats to hold a small, untested sample of each unknown. 

1 How We Are Finding Out about the Unknowns list (from Lesson 3) 1 plastic funnel 

Put vinegar labels on the 15 dropper bottles and fill them with vinegar. Place the bottles in the materials center. 

Add the vinegar bottle strip to the Check Your Science Pail poster. 

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Your students have carried out two physical tests (water drop and water mixtures) and four chemical tests (vinegar, iodine, red cabbage juice, and heat) on the unknown solids. In this lesson, they review and analyze all the data they have collected as a result of performing these tests to determine the distinctive properties of each unknown. This process provides students with the information and skills they need to solve the mystery in Lesson 12. 

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