CHEMISTRY NOW: Kitchen Mystery-Source of Unknown Solid? (Grades 9-12)
Students will carry out a series of chemical reactions involving common household chemicals and make observations. Students will be able to use their observations to distinguish between several similar- appearing substances. Students will be able to use their observations of an unknown substance to determine which of the original substances it is. Students will design and carry out an inquiry-based experiment
CHEMISTRY NOW: Kitchen Mystery-Source of Unknown Solid?
Subject Area: Chemistry
Grade Level: High School Chemistry
Title: Kitchen Mystery
National Science Standards:
Teaching Standard – A: Planning an Inquiry-Based Science Program
Assessment Standard – C: Using Authentic Assessment Opportunities
Physical Science Standards: Structure and Properties of Matter
Suggested Prior Knowledge: concepts of compounds, chemical reactions/changes
Purpose: To allow students to observe a series of chemical reactions involving common kitchen chemicals, and use their observations to design and carry out an experiment to determine the identity of an unknown kitchen chemical.
chemical compound – a is a chemical substance consisting of two or
more different chemically bonded chemical elements, with a fixed ratio determining the composition
chemical property – a property shown by a substance when it reacts with a different substance or undergoes a change in composition
1. Students will carry out a series of chemical reactions involving common household chemicals and make observations
2. Students will be able to use their observations to distinguish between several similar- appearing substances
3. Students will be able to use their observations of an unknown substance to determine which of the original substances it is
4. Students will design and carry out an inquiry-based experiment
- Small containers for solids (old film canisters work well)
- Small droppers to dispense liquids
- Labeling pens or wax pencils
- Baking soda
- Powered Sugar
- Baking Powder
- Tincture of iodine or Lugol’s solution
A. Introduce the lesson by providing students with a list of the materials. Discuss with students the basic idea: they have a container of a white solid that is no longer labeled (the “unknown”). They have samples of several labeled similar substances and several liquids to use to try to figure out what the unknown substance is. Some leading questions include:
- How can you distinguish between the known substances?
- How much evidence do you need to be sure you can clearly tell the known substances apart?
- How can you figure out what the unknown substance is?
B. Work with students to develop a procedure that will allow them to determine some properties of the known substances, and will allow them to identify the unknown solid. Lead the students toward a technically correct experiment that will yield correct results.
C. Be certain that lab safety protocols are followed and safety equipment such as goggles are used. Remind students that although these are household substances, students should never taste anything in the experiment.
D. Encourage students to keep careful notes of their procedure(s) and of all observations. If your students have the necessary skills to develop a data table, ask them to build whatever table they feel is needed to identify the unknown substance. If not, suggest they build a matrix of solids and liquids, so that they are able to test all substance combinations and record the results.
E. It is more challenging if there are several samples of unknowns and student groups each have different ones. This keeps them from trying to copy each other’s work, and from second-guessing their own.
F. It is best to provide each group of 2-3 students with small, labeled containers of the known substances and a separate unlabeled container of the “unknown.”
G. This can be done in microscale with notebook sheet protectors used as the reaction surface and using coffee stirrers to “scoop” solids and droppers for the liquids.
H. Conclude this activity by asking the following questions to prompt a class discussion:
- In what ways could you have improved your experiment?
- What were some challenges you encountered in creating your experiment?
Student Worksheet for Kitchen Mystery
Name: _____________________________________ Date: ______________
- baking soda
- powered sugar
- baking powder
- tincture of iodine
- plastic sheet protector
1. Design an experiment to distinguish among the white solid kitchen chemicals and use this information to determine the identity of the “unknown” white solid.
2. Be sure that your procedure is detailed and clearly outlined. Make sure that you follow standard safety protocols and wear goggles.
3. Carefully record all of your procedure steps and observations in appropriate data tables.
Student Procedure: ___________________________________________________