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Course: High school chemistry > Unit 10
Lesson 3: Unit 8 activitiesActivity: Why does food in a refrigerator stay fresh for longer?
Make science come alive in your classroom with this free hands-on activity aligned to high school NGSS standards.
Activity: Why does food in a refrigerator stay fresh for longer?
You might not think of a refrigerator as revolutionary, but modern refrigeration has transformed the way we eat. It allows us to store fresh foods for longer periods of time, so we can make fewer trips to the grocery store, and it allows us to ship produce all over the world. As a result, we can eat our favorite fruits and vegetables all year round, even when they are not in season where we live or can only be grown in environments different from those where we live.
Maybe you have seen apple slices left out on a plate turn brown or observed an avocado become softer and change color from green to nearly black over several days. These processes by which fruits ripen and eventually decompose involve many chemical reactions.
So, why does an apple stay crisp longer or an avocado ripen more slowly in a refrigerator? How does your refrigerator slow the chemical reactions involved in ripening and decomposition? In this activity, you’ll investigate several factors that affect the rates of chemical reactions and use your knowledge of collision theory to develop an explanation.
Overview
This activity is designed to be completed in two or three 45-minute class periods, with additional time required for follow-up creative projects. The activity consists of the following parts:
- Setting the stage—Students review fundamental concepts related to collision theory, temperature, and concentration that will prepare them to investigate and explain factors that affect the rates of chemical reactions. (15 minutes)
- Investigation (Part 1)—Students observe the effect of changing temperature on the rate of a chemical reaction between sodium bicarbonate and citric acid when an Alka-Seltzer tablet is placed in water. Students use their experimental data and their understanding of collision theory to identify and explain the relationship between temperature and reaction rate. (30 minutes)
- Investigation (Part 2)—Students observe the effects of changing reactant concentration on the rate of a chemical reaction between sodium bicarbonate and acetic acid. Students use their experimental data and their understanding of collision theory to identify and explain the relationship between reactant concentration and reaction rate. (25 minutes)
- Investigation (Part 3)—Students use their understanding of collision theory to make and test predictions about the effect of changing the surface area of a solid on the rate of a chemical reaction. (20 minutes)
- Investigation (Part 4)—In this optional extension, students use their learning from Parts 1-3 to design and carry out an experiment to investigate the effect of stirring on the rate of a chemical reaction. (45 minutes)
- Let's get creative!—Students apply their knowledge to create slides for a “Kitchen Chemistry” class that explain why putting produce in a refrigerator allows it to stay fresh longer. (45 minutes)
- Keep creating!—Students can choose from additional project ideas. Each project encourages students to combine scientific knowledge with creativity to produce something new.
Download the worksheets and get started today!
You can print out this activity or upload it to a digital classroom.
- Student activity guide (17 page worksheet)
- Teacher guide (step-by-step instructions)
NGSS performance expectations
HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
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