Natural Vs. Synthetic Polymers

Natural vs. Synthetic Polymers Dan Polon and Lauren Kucera Grade level: 9

Lesson Source: 1. http://www.youtube.com/watch?v=pIvAl4lu1uA, Plastic Milk Experiment. This was modified by using milk at room temperature and extra vinegar. 2. http://www.chem.umn.edu/services/lecturedemo/info/Nylon_Rope_Trick.html, Nylon Rope Trick. This was also modified by including a few flakes of phenolphthalein.

Objectives: 1. Compare and contrast the structure, properties, and principle functions of carbohydrates, lipids, proteins, and nucleic acids in living organisms. (DOK 2) 2. Examine the life processes to conclude the role enzymes play in regulating biochemical reactions. (DOK 2)

What should students know as a result of this lesson? The student will be able to: identify monomers and polymers, describe the relationship between monomers and polymers, compare and contrast the differences between natural and synthetic polyamides, identify the enzyme-substrate complex, describe the function of enzymes in living organisms.

Materials needed: Milk (room temperature), vinegar, 250 mL beakers, funnels, 100 mL graduated cylinders, paper towels/coffee filters, plastic spoons, hexamethylenediamine, sodium hydroxide, DI water, sebacoyl chloride, hexanes, phenolphthalein, glass stir rods, balances, safety goggles, gloves, salt, nylon, milk jugs, bouncy ball.

Procedures: Engage: To engage the students bell work will be assigned that asks the students to classify different materials as either polymeric or not. The materials that the students are to classify will be given to them so that they can observe the physical properties. Materials will include water, salt, nylon, milk jugs, bouncy ball, etc. Then the teacher will discuss with students the definition of a polymer and monomers, and answer any student questions.

Explore: Once the students know the definition of polymer the teacher will do the nylon rope trick demonstration. The chemicals needed for this demonstration can be prepared in advance or in front of the class. To make the first solution, 6 g of hexamethylenediamine, 2 g of sodium hydroxide, and 100 mL of DI water are added to a bottle. These chemicals are stirred until the solids have completely dissolved. Finally a few flakes of phenolphthalein (not much is needed!) are added to give the solution a distinct pink color. In a second bottle, 2 g (1.6 mL) of sebacoyl chloride and 100 mL of hexanes are combined and stirred until mixed. To perform the demonstration, 50 mL of the hexamethylenediamine solution (the pink solution) is measured out into a 250 mL beaker. 50 mL of the sebacoyl chloride solution is slowly added to the pink solution by pouring down the side of the beaker. This will form two distinct layers with the polyamide forming at the interface. A glass rod can be used to pull out the polymer and the polymer strand can be wrapped around the glass rod. This will continue until there is no monomer left. This demonstration will really emphasize the fact that polymers can be very long chains. Also it will give the students an experience with seeing a polymer created from monomers.

Explain: The nylon rope trick will be used to lead right into a lecture on the difference between natural and synthetic polymers, specifically focusing on polyamides. During the discussion it will be emphasized that proteins and nylons share the same amide linkage, however proteins are made in the body using amino acids and the nylon is made in labs using different techniques. Also the different functions of nylons and proteins will be discussed with emphasis on the role of enzymes.

Elaborate: To emphasize to the students that natural and synthetic polymers can look very different, the students will now have the opportunity to extract protein from milk. By doing this experiment they will still be looking at polymers with the same amide linkage. To perform this experiment it will be easiest for students to work in pairs or groups. Each group will measure out 100 mL of milk (room temperature) into a 250 mL beaker. They will then add 50 mL of vinegar. They can mix the solution with a plastic spoon and observe the milk separating. They will then make a filter cone out of paper towels or use a coffee filter to separate the protein from the rest of the milk (whey). The filter will be placed in the funnel, which will allow the whey to drip into the graduated cylinder. This process will take a long time and the milk/vinegar solution should be added over time. The protein should be left to dry overnight in the filter and the next day will be a hard plastic material.

Evaluate: Informal evaluation will be used throughout the entire class period. Discussions where the students are involved allows for the teacher to determine the students understanding. During both the nylon rope trick demonstration and the plastic milk experiment the students will be asked to write a list of observations, which will help them to improve their scientific writing. Finally a formal evaluation will be given as the bell ringer at the start of the next class period in the form of a quiz over material covered in the discussion.