Summary

In this lab, students will perform a simple chemical reaction in a closed system to produce a small amount of gas. They will collect mass measurements for the reactants and the products in order to demonstrate the conservation of mass during the reaction. They will also release the produced gas from the closed system in order to verify that gasses have mass.

Grade Level

Middle or High School

NGSS Standards

• 5-PS1-1: Develop a model to describe that matter is made of particles too small to be seen.
• MS-PS1-1: Develop models to describe atomic composition of simple molecules and extended structures.
• MS-PS1-5: Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.

Objectives

By the end of this lab, students should be able to

• Differentiate between a closed and open system.
• Specify between reactants and products in a chemical reaction.
• Describe the law of conservation of matter/mass.
• Explain how the law of conservation of matter/mass applies within open and closed systems.

Chemistry Topics

This lab supports students’ understanding of

• Chemical Reactions
• Law of Conservation of Mass
• Observations
• Measurement

Time

Teacher Preparation: 30-40 minutes

Lesson: 30-45 minutes

Materials (per group)

• Glass vial w/ lid
• 1 small piece of tape (masking or scotch)
• 1/8 tablet of Alka-Seltzer or equivalent tablet.
• Water
• Electronic Balance

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Do not consume lab solutions, even if they’re otherwise edible products.
• Food in the lab should be considered a chemical not for consumption.
• This lab produces a gas in a closed system, it is extremely important that you only use small amounts of substance that can be contained in the containers. Teachers must monitor your students to ensure they don’t use more than the 1/8^th tablet recommended. Larger quantities could create pressures that could rupture the container.

Teacher Notes

• It will be helpful if the teacher breaks the tablets into appropriately sized chunks for the students (about 1/8 tablet) in advance of the lab. This will help ensure students use the appropriate amount and are not tempted to put larger chunks into their container. As mentioned in the Safety section it is extremely important that only small amounts of substances are used in order to ensure the vial does not break.
• As an alternative to using a glass vial, you could try performing this using a Ziploc bag. You would need to keep the dry tablet away from water until after the bag is sealed. You can reference the AACT demonstration Comparing Chemical Reactions for guidance about completing the reaction in a Ziploc bag.
• The procedures will instruct the students to tape the tablet to the inside of the lid so that they can close the system and measure the total mass of all of the reactants before the reaction occurs.
  • Make sure your students understand how to roll tape back on itself to make it 2 sided, and maybe demonstrate this for them.If the tablet falls off prematurely, the data will not be useful.
  • The tape sticks best to a dry lid, so if possible, leave time for lids to dry, or make sure students dry them well between uses.
• As an optional component, students could repeat the procedure to collect data in a second trial for data comparison.