This lesson is based on California's Middle School Integrated Model of NGSS.
NGSS Performance Expectation (PE): (MS-PS1-2) Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occured.
Science and Engineering Practice (SEP) 3: Planning and Carrying out Investigations
Disciplinary Core Ideas (DCI): PS1.A: Structure and Properties of Matter - Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms.
Crosscutting Concepts (CCC) 2: Cause and Effect - Cause and Effect relationships may be used tp predict phenomena in natural or designed systems.
This lab is designed to provide the students with a simple, safe, and effective method of testing if surface area can increase the rate of a chemical reaction. Students will time the difference in reaction rates between a whole Alka Seltzer tablet and a crushed Alka Seltzer tablet. Since the crushed tablet exposes more particles to the reacting water it will react at a faster rate. Mixing Alka Seltzer and water is the cause and the production of carbon dioxide bubbles in the effect (CCC2). This lesson allows my students pose testable questions (does surface area increase reaction rate?) and plan effective labs to seek the answer (unPD - support students designing effective investigations).
Trial 1 - whole tablet
Trial 2 - crushed tablet
Pass out a copy of the Surface Area Lab to each student. I provide all the necessary supplies and safety goggles in a plastic box at the center of each table. It is imperative that students wear safety goggles for this activity.
I tell my students that they are going to compare the rate of two reactions. One reaction will be with a whole Alka Seltzer tablet and water producing carbon dioxide bubbles. The other reaction will be with a crushed Alka Seltzer tablet and water producing carbon dioxide bubbles. The difference between the two reactions is the surface are of the Alka Seltzer tablets exposed to the water. More surface area produces a faster reaction rate.
The chemical formula that describes this reaction is:
This formula may be overwhelming to eighth graders so I typically explain that an Alka Seltzer tablet when exposed to water will produce carbon dioxide bubbles.
When it comes time to crushing the tablet I have the kids place the tablet between a folded sheet of paper and hit the tablet with a textbook. Use the folder paper to help slide the crushed tablet into the beaker of water.
Crushed Alka Seltzer Tablet and water.
As part of this assignment the students are required to develop a question they want to ask, form a hypothesis of what they think will happen, record data relating to the question, and state their conclusion based on the data.
They also have to answer four questions in complete sentences.
Example of Student Work
I created a Powerpoint: Rates of Chemical Reactions that describes the factors of how chemical reactions can be increased. This lesson has the students crushing an Alka Seltzer tablet which increases the amount of the tablet exposed to the reacting water.
I created a mnemonic sentence to help with remembering the four factors that increase the rate of reactions:
Camels swim to Catalina
For review I have also included: Evidence of a Chemical Reaction. This covers the evidence needed in order to prove a chemical reaction has occurred.
I created another mnemonic sentence to help students remember the evidence of a chemical reaction.
Cats tell stories of ghosts.