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 (SP) 3: Analyzing and Interpreting Data
Disciplinary Core Ideas (DCI): PS1.A: Each pure substances has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it.
Crosscutting Concepts (CCC): Patterns - Macroscopic patterns are related to the nature of microscopic and atomic-level structures.
Suspensions are mixtures that do not evenly distribute their contents in a container. By comparing and contrasting suspensions and solutions, suspensions would be like a salad where every bite is different and solutions are like vanilla pudding where every bite is the same. Use the activity Solutions Lab to compliment this one.
During this laboratory activity no chemical reaction takes place (MS-PS1-2), water and corn starch are simply mixed together (PS1.A). The students follow precise directions to create a suspension mixture, often referred to as oobleck. Once they have created oobleck they attempt to determine if a chemical reaction has taken place (see Types of Chemical Reactions for review), examine the physical properties of oobleck (CCC), and attempt to determine its physical characteristics (SP3). Oobleck is defined as a non-newtonian mixture, it can simultaneously exist as a solid and a liquid.
This mixture got its name from a Dr Seuss' book "Bartholomew and the Oobleck" - a spoiled king wanted his court magicians to create a fourth state of matter and Bartholomew, a royal squire, has to clean up the consequences. If time permits I read this book to my class after the activity. My eighth graders love to be read picture books.
TIP: To correctly measure the proper amount of corn starch, I have my students first estimate the amount by volume then transfer this amount to a paper box and weigh the contents. Determining the amount by weight is a far more accurate method, as required to make a sample of oobleck.
TIP: I allow my students to pour the oobleck on their desks to experiment with. Oobleck cleans up very nicely once it dries. During clean-up, I instruct my students to throw as much away as possible then wipe the remaining oobleck with a paper towel and allow it to dry into a fine powder. Then it can then easily sweep it up.
FUN: As a Halloween activity I once substituted food coloring with Steve Spangle's Atomic Glow Concentrate and positioned black lights around my room. When the lights were turned out the oobleck glowed a eerie green under the black lights - big hit of the day!
The secret to success with the Suspension Lab (Oobleck) is the students' ability to follow precise multi-step instructions, using scientific equipment to correctly measure required amounts of corn starch and water. I typically wander around the classroom and adjust their mixtures depending on if the student's oobleck is too runny or too dry. Adding a spoonful of water or corn starch does the trick in order to achieve the correct consistency.
TIP: Provide as little guidance as possible. This a a safe activity that looks messy, but isn't. Give your students the freedom to experiment and play (see Reflection - Discovery through play).
Weighing the corn starch (step 2).
Transferring the corn starch to the large beaker (step 3).
Mixing corn starch and water (step 6).
Determining the properties of oobleck (step 8).
Student Work Sample
To better assist my students in learning about solutions and suspensions I teach the following memory devise.
SOLUTE + SOLVENT = SOLUTION
The solute is the material that is dissolved and the solvent is the material that is doing the dissolving to form the solution. In other words salt (solute) is dissolved in water (solvent) making saltwater (solution).
I teach my kids to count the letters. Salt is the smallest letter and it represents the smallest ingredient (solute - 6 letters). Water is the next largest ingredient and it is represent with a larger word (solvent - 7 letters). Saltwater is the large result in this example and it is represented with the largest word (solution - 8 letters).
I have created a Solutions PowerPoint lesson that can be used with your students that reviews solutions and suspensions.