Sticky Situation Learning Objectives: Students learn that some mixtures can be separated using chemical properties. GRADE LEVEL SNEAK PEAK inside … 3–8 ACTIVITY SCIENCE TOPICS Students make and test glue, which they make from mixing milk and vinegar. Atoms and Molecules Chemical Reactions STUDENT SUPPLIES Industrial Chemistry see next page for more supplies non-fat powdered milk vinegar PROCESS SKILLS sturdy paper towels or coffee filters baking soda, etc…. Describing and Defining Measuring ADVANCE PREPARATION see next page for more details GROUP SIZE Make milk from milk powder Fill bottles with vinegar, etc…. 2–3 OPTIONAL EXTRAS DEMONSTRATION Glue Show and Tell (p. F - 40) EXTENSIONS Glue Inventions (p. F - 44) TIME REQUIRED Advance Preparation Set Up Activity Clean Up 10 minutes 10 minutes 30 minutes 10 minutes Sticky Situation F - 37 Chemistry in the K–8 Classroom Grades 3–8 2007, OMSI SUPPLIES Item Amount Needed non-fat dry milk powder 1 cup per class water 3–6 cups per class vinegar ¼ cup per group baking soda 1 tsp per group pop-top squeeze bottles (e.g., water or sports drink) 2 per group plastic cups 3 per group wooden craft sticks (e.g., popsicle sticks) 1–2 per group plastic spoons 1–2 per group strainers several for class to share scraps of paper 5–8 per group For Extension or Demonstration supplies, see the corresponding section. ADVANCE PREPARATION Supplies Preparation Milk Solution: This recipe makes a total of 4 cups of milk solution, or enough for 16 groups. Adjust the recipe if you have more groups than this. Add 1 cup of non-fat dry milk powder to 3 cups of water. Mix well. Fill pop-top squeeze bottles with about ¼ cup in each bottle. Label these bottles “milk.” Vinegar Fill pop-top squeeze bottles with about ¼ cup of vinegar. Label these bottles “vinegar.” Baking Soda Fill plastic cups with about 1 teaspoon of baking soda. Label these cups “baking soda.” Sticky Situation F - 38 Chemistry in the K–8 Classroom Grades 3–8 2007, OMSI SETUP For each group milk in pop-top squeeze bottle vinegar in pop-top squeeze bottle baking soda in plastic cup 2 empty plastic cups 1–2 plastic spoons 1–2 wooden craft sticks sturdy paper towel or coffee filter 5–10 scraps of paper At a central location (or with the teacher) several strainers for class to share towels and sponges for clean up INTRODUCING THE ACTIVITY Let the students Students will use milk and vinegar to create a glue that can stick speculate before paper together. offering answers to any questions. The What does glue look like? What does it feel like? Or smell like? answers at right are Glue is sticky. Some glue is liquid when you use it, but it dries hard. provided for the teacher. Some dries like a thin skin. Some glues are stronger than others. Some glues have a strong smell. Choose questions that are Are all glues the same? How are they the same? How are they different? appropriate for Glues are not all the same. Examples include: white liquid school your classroom. glue, clear or bluish school glue, yellowish liquid mucilage glue, solid glue sticks, strong-smelling industrial-strength glue, epoxy that must be mixed, fast-drying superglue, spray glue, hot-glue-gun gel sticks, yellow wood glue, slow-drying book-bonding glue, denture glue, etc. Why are there so many different kinds of glue? Each glue is designed for a different purpose. Each surface (paper, wood, cloth, glass, plastic, fabric) needs a different kind of glue to stick together. Some glues are permanent (super glue) but some are temporary (Post-it Notes, cereal boxes). Some glues need to be waterproof (denture glue). CAUTION: Students should never put lab supplies in their mouths. Even if lab supplies are foods, they may be contaminated by other items in the lab. Sticky Situation F - 39 Chemistry in the K–8 Classroom Grades 3–8 2007, OMSI TEACHER DEMONSTRATION Glue Show and Tell Bring a variety of different kinds of glue to show students. Discuss the properties of each glue and how it is specially designed for its purpose. You can also work with students to create categories for the different glues. Some examples are listed to help you get started. Non-Toxic Waterproof Weak vs. Strong glue stick super glue Post-it Notes white glue fabric glue stickers clear glue wood glue labels Post-it Notes stickers super glue stamps epoxy rubber cement denture glue Sticky Situation F - 40 Chemistry in the K–8 Classroom Grades 3–8 2007, OMSI CLASSROOM ACTIVITY Have students follow the Scientific Procedure on page F - 47, working in groups of 2–3. Below are suggestions to help the teacher facilitate the activity. NOTES This handout is on p. F - 47. Running Suggestions When students mix the milk and vinegar together, they will notice a strong “sour milk” smell. This reaction is similar to the reaction that occurs when bacteria spoils milk, so it makes a similar smell. Test the experiment yourself with a paper towel or coffee filter. If your filter does not work well (it filters too slowly or it breaks), try other methods. Coffee filters are stronger, but also tend to filter slowly. Paper towels will filter faster but are weaker. To minimize messes, encourage students to do all their experiments on a cafeteria tray. You may want to have students answer questions and draw pictures on separate pieces of paper so they will have more space. Ongoing Assessment Encourage students to make careful observations of what happens to the milk as vinegar is added. Where do the solid parts come from? (The milk is changing from liquid to solid.) Is all of the milk changing to a solid? (No, some parts stay liquid.) Sticky Situation F - 41 Chemistry in the K–8 Classroom Grades 3–8 2007, OMSI Safety and Disposal All materials may be thrown in the trash when finished. Refrigerate unused milk solution and use within two weeks. CAUTION: Students should never put lab supplies in their mouths. Even if lab supplies are foods, they may be contaminated by other items in the lab. CLASSROOM DISCUSSION Ask for student The sticky substance students made in this activity is able to glue observations and paper together. Although it may not seem sticky at first, once it explanations. Let the students guide dries, the paper should stay together very well. the discussion and present their What happened when vinegar was added to the milk? hypotheses before It clumped, or became solid (curdled). It smelled bad, like spoiled discussing explanations. milk. A chemical change occurred. The liquid milk separated into solid white curds and clear liquid whey. Choose questions that are What happened when baking soda was added to the curds? appropriate for your Bubbles appeared. The baking soda (a base) reacted with the classroom. vinegar (an acid) to produce a gas (carbon dioxide). Have you heard the rhyme “Little Miss Muffet sat on her tuffet eating her curds and whey…”? Have you ever eaten curds or whey? Most cheeses are made from the curds of milk. Cottage cheese is the most obvious example. Spoiled milk also forms solid curds. Whey is the liquid part of milk. Low-fat milk and non-fat milk have more whey than whole milk. What would happen if you change the formula (or recipe) for this glue? For example, what if you use less vinegar in the formula? Let students predict what they think will happen in different scenarios. The glue might be more sticky, less sticky, more liquid or more solid. The glue could dry really fast or dry very slowly. Record students’ suggestions for use in Extension A. This extension allows students to experiment in creating different glue recipes. Sticky Situation F - 42 Chemistry in the K–8 Classroom Grades 3–8 2007, OMSI EXPLANATION This background information is for teachers. Modify and communicate to students as necessary. In this activity, students discovered that milk and vinegar react to create a sticky solid. This solid can be used to make paper stick together. What’s in Milk Milk is a mixture of water, milk sugar (lactose), fats, protein, and small amounts of other nutrients, such as vitamins and minerals. Milk is a special kind of mixture known as an emulsion since it has several components that do not dissolve in one another. The fats and proteins are in tiny droplets that are suspended in the water of the milk. Other emulsions students may be familiar with are mayonnaise and some salad dressings. Students can look on the ingredient labels for items listed with the description “added as an emulsifier” or “added as a stabiliser.” An emulsifier is anything added to make two liquids that won’t dissolve (like oil and vinegar) to stay mixed together. Separating Milk Protein The major protein in cow’s milk is called casein. Casein, like other proteins, has a three-dimensional shape that determines its behavior, its characteristics, and its properties. If the shape of the protein changes, then the properties of the protein will change. When the shape of a protein is changed, it is called denaturing the protein. Denatured proteins can look and act differently. One way to denature a protein is through heat. The protein in egg whites (called albumin) turns from a clear liquid to a white solid when it is heated. Another way to denature a protein is by adding an acid. When students add vinegar (an acid) to the milk, the casein in the milk changes its shape and becomes denatured.