LAB 014: Polymers. A) OBJECTIVE Observe the effect various ratios of mixtures have on the physical properties of a compound. Determine B) BACKGROUND

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1 A) OBJECTIVE Observe the effect various ratios of mixtures have on the physical properties of a compound. Determine ratios and percentages of the mixtures. B) BACKGROUND Chemical properties are qualities that can be observed during a chemical reaction, like when vinegar reacts with baking soda. Physical properties are qualities that can be observed during physical change in the absence of a chemical reaction, like the melting of an ice cube. Physical properties can be used to describe the state of a chemical, which can be a solid, liquid or gas. The physical properties of Silly Putty are what make it so much fun because it is a polymer that is stretchy and bouncy. A POLYMER is a large MOLECULE composed of repeating units typically connected by COVALENT BONDS. Although the term POLYMER commonly refers to plastics, it includes a large class of natural and synthetic materials with a wide variety of properties Scientists use descriptive language to describe physical properties: hot, cold, squishy, hard, soft, crystalline, granular, smooth, liquid, clear, opaque, runny. COVALENT BOND: sharing of electrons between atoms MOLECULE: A group of at least two atoms held together by covalent chemical bonds POLYMER: a large molecule composed of repeating structural units B) PROCEDURE NOTE: Pay attention to TEASPOONS (5ml) and TABLESPOONS (15ml)! Step 1. Prepare Solution #1, the 50% glue solution, which is made up of half glue (50%) and half water (50%) by adding one cup of glue and one cup of water to a container. Label this container Solution #1 GLUE. Step 2. Step 3. Secure the lid and shake until glue is fully diluted and no gooey clumps remain. Prepare Solution #2, the Borax solution, which is made up of 4% Borax in water. Usually you would weigh the borax, but you can approximate this solution by adding 2 TEASPOONS of Borax to 1 cup of warm water to a jar. Label this container Solution #2 BORAX. 1

2 Step 4. Tightly secure the lid and shake until no particles of Borax remain and the solution is clear. Step 5. Label four Zip-lock baggies Sample #1, Sample #2, Sample #3, and Sample #4. Step 6. Step 7. Step 8. Add 1 TABLESPOON of Solution #1 GLUE and 3 TABLESPOONS of Solution #2 BORAX to the baggie labeled Sample #1. Seal the baggie and squish around to mix the ingredients. Record your observations in D) DATA. Write down your description of the physical properties of the material in your table. Use descriptions such as runny, slimy, sticky, hard, soft, bouncy, etc. Add 2 TABLESPOONS of Solution #1 GLUE and 2 TABLESPOONS of Solution #2 BORAX to the baggie labeled Sample #2. Step 9. Repeat Step 7 Step 10. Add 3 TABLESPOONS of Solution #1 GLUE and 1 TABLESPOON of Solution #2 BORAX to the baggie labeled Sample #3. Step 11. Repeat Step 7. Step 12. Add 4 TABLESPOONS of Solution #1 GLUE and 1 TABLESPOON of Solution #2 BORAX to the baggie labeled Sample #4. Step 13. Repeat Step 7. 2

3 D) DATA STEP SAMPLE Solution #1 GLUE Solution #2 BORAX OBSERVATIONS PHYSICAL PROPERTIES Tbsp 3 Tbsp Tbsp 2 Tbsp Tbsp 1 Tbsp Tbsp 1 Tbsp E) CALCULATIONS Calculate the RATIO of glue to borax for each of the Samples: SAMPLE 1: TBSP GLUE to TBSP BORAX = to or : SAMPLE 2: TBSP GLUE to TBSP BORAX = to or : SAMPLE 3: TBSP GLUE to TBSP BORAX = to or : SAMPLE 4: TBSP GLUE to TBSP BORAX = to or : Calculate the PERCENTAGE glue in each of the Samples: 3

4 SAMPLE 1: TBSP GLUE to TBSP BORAX = SAMPLE 2: TBSP GLUE to TBSP BORAX = SAMPLE 3: TBSP GLUE to TBSP BORAX = SAMPLE 4: TBSP GLUE to TBSP BORAX = F) QUESTIONS 1) Which ratio of ingredients produced the best product? 2) What will you call your new product? 3) Why did varying amounts of mixtures create different results? G) DESIGN CHALLENGE How would use what you ve learned to improve your design? H) GLOSSARY Compound: Covalent Bond: a form of chemical bonding that shares electrons between atoms Molecule: A group of at least two atoms held together by covalent chemical bonds Mixture: Polymer: a large molecule composed of repeating structural units Ratio: Tablespoon: 4

5 Teaspoon: VISCOSITY: I) UNDERSTANDING When you mix Elmer's glue with a bit of water, you make a substance that is known as a polymer (polyvinyl acetate) and that the borax solution (sodium tetraborate) is a 'cross-linking' substance that binds the polymer chains together to make the glue solution thicker. So, as the polymer chains get more 'bound-together', it gets harder for them to move around, and your slime starts to be more like Silly-putty. Experiment with adding more borax solution to see if this indeed makes the slime thicker or thinner. The mixture of Elmer s Glue with Borax and water produces a putty-like material called a polymer. In simplest terms, a polymer is a long chain of molecules. You can use the example of cooking spaghetti to better understand why this polymer behaves in the way it does. When a pile of freshly cooked spaghetti comes out of the hot water and into the bowl, the strands flow like a liquid from the pan to the bowl. This is because the spaghetti strands are slippery and slide over one another. After awhile, the water drains off of the pasta and the strands start to stick together. The spaghetti takes on a rubbery texture. Wait a little while longer for all of the water to evaporate and the pile of spaghetti turns into a solid mass -- drop it on the floor and watch it bounce. Many natural and synthetic polymers behave in a similar manner. Polymers are made out of long strands of molecules like spaghetti. If the long molecules slide past each other easily, then the substance acts like a liquid because the molecules flow. If the molecules stick together at a few places along the strand, then the substance behaves like a rubbery solid called an elastomer. Borax is the compound that is responsible for hooking the glue s molecules together to form the putty-like material. There are several different methods for making this putty-like material. Some recipes call for liquid starch instead of Borax soap. Either way, when you make this homemade Silly Putty you are learning about some of the properties of polymers. Elmer's Slime is very easy to make, but it's not exactly what you'll find at the toy store. So, what's the "real" slime secret. It's an ingredient called polyvinyl alcohol (PVA). The cross-linking agent is still Borax, but the resulting slime is longer lasting, more transparent... it's the real deal. 5

6 Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water. Borax has a wide variety of uses. It is a component of many detergents, cosmetics, and enamel glazes. It is also used to make buffer solutions in biochemistry, as a fire retardant, as an anti-fungal compound for fiberglass, as an insecticide, as a flux in metallurgy, a texturing agent in cooking, and as a precursor for other boron compounds. The term borax is used for a number of closely related minerals or chemical compounds that differ in their crystal water content, but usually refers to the decahydrate. Commercially sold borax is usually partially dehydrated. The word borax is from Persian and originates in the Middle-Persian būrak Viscosity is defined as the quality of liquid to resist flow. Materials which have a low resistance to flow, or flow quickly, such as water, have a low viscosity. Liquids which flow slowly, such as honey, have a high viscosity. The Elmer's glue used in this experiment has a high viscosity due to the fact that it consists of a large number of particles dispersed in water. As the glue is diluted with water, the number of dispersed particles decreases, lowering the viscosity of the resulting liquid ATOMS ---- MOLECULES POLYMERS 6

7 Agee, PH.D., Science Buddies, Reference: Sara 7