Students help design a test using baking soda, corn starch, and cream of tartar to investigate the question: Which two of the three ingredients in baking powder react to make it bubble when water is added?
Objective
Students will be able to plan and carry out an investigation to identify which two of the three ingredients in baking powder react to produce a gas when water is added. Students will be able to explain that mixing substances can cause a chemical reaction that results in the formation of a new substance. Students will also be able to explain that substances react in characteristic ways and that the way a substance reacts can be used to identify the substance.
Key Concepts
- Mixing substances can result in a chemical reaction that produces new substances.
- Substances have characteristic chemical reactions that can be used to identify them.
- Designing a fair test to study chemical reactions requires keeping all variables the same except for the one you want to know about.
NGSS Alignment
- NGSS 5-PS1-3: Make observations and measurements to identify materials based on their properties.
- NGSS 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in new substances.
Summary
- In a demonstration, students see that baking powder reacts with water to produce a gas but baking soda does not.
- Students are told that baking powder is a mixture of three ingredients (baking soda, cream of tartar, and cornstarch) and that two of these ingredients react to produce a gas when water is added.
- Students are guided to design a test to determine which two of the three ingredients in baking powder react to make it bubble when water is added. (The answer is baking soda and cream of tartar.)
- Finally, students will watch a demonstration of an effervescent tablet, such as Alka-Seltzer, which fizzes when it dissolves in water. The reaction that causes this fizzing is similar to the reaction that occurs when baking powder and water are combined.
There are three main ideas in this activity:
- How to design a valid experiment
- Mixing substances can result in a new substance (carbon dioxide gas)
- The way different substances react is a characteristic property that can be used to identify a substance
Evaluation
Download the student activity sheet (PDF) and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan.
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