CHEM 1405 Brookhaven College Chemistry Lab Report

SLIME – Observations of a PolymerCHEM 1405 Laboratory Experiment
Introduction
Polymers are long molecules that are formed through polymerization reactions which combine many smaller
molecules called monomers. The polymerization reactions chemically connect the monomers in chains of
varying length. For example, in this experiment, you will be using polyvinyl alcohol, which is a polymer built
from vinyl alcohol, which has the chemical formula, C2H4O. The formula of polyvinyl alcohol is written
(C2H4O)n.
The number of repeating monomers (“n” in the formula above) in a polymer is called the degree of
polymerization. In the polymer made in this lab, n will be around 2,300.
Depending upon the monomers used, polymers can be linear, branched, and cross-linked as shown in Figure 1.
As polymers become more branched or cross-linked, their properties change. More cross-linking yields a more
rigid polymer is an example of such a change in properties.
Figure 1: Illustration of types of polymers
Linear
Branched
Cross-linked
Polymers can be either natural or synthetic. Natural polymers include things like proteins, nucleic acids, silk
and wool. Nylon, Teflon, plastics and Plexiglas are examples of synthetic polymers.
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Experimental Overview
Good science depends upon good observations. In order to understand what is going on in an experiment, we
must pay careful attention to how our chemicals behave and what changes are taking place. We quantify
many things by measuring them- mass, volume, density, etc. are all things for which we record numbers and
make calculations. Equally important are the qualitative observations we make- What did it look like? What
did it smell like? What was its texture? Was it a solid, a liquid, or a gas?
This experiment will introduce you to the laboratory balance, the Bunsen burner and the glassware typically
used in the lab. It will also give you practice in making observations.
Experimental Procedure
Prior to the lab: Watch the balance, Bunsen burner and glassware videos found on eCampus.
1. Obtain approximately 25mL of the Polyvinyl Alcohol (PVA) solution in a clean 250mL beaker and set it aside.
2. Weigh out approximately 1g of Borax into a clean 50mL beaker.
3. Place about 25mL of deionized water (DI Water) in a clean 100mL beaker. Heat the water almost to boiling
using a Bunsen burner and add the Borax slowly to the water while stirring. When dissolved in water, Borax
2(sodium tetraborate) dissociates into hydrated sodium (Na+) and tetraborate (B O ) ions.
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4. Add a few drops of food coloring to the PVA solution. Then, using a pipet, add approximately 5mL of the
Borax solution, drop by drop, to the PVA while constantly stirring. The tetraborate ions react with the
hydroxyl groups (-OH) of the PVA forming cross links with the probable elimination of water. Hydrogen
bonding is also involved in forming the cross links which break and reform as the slime flows.
5. After you are finished adding the 5mL of the Borax solution, a viscoelastic gel should have formed which can
be removed from the beaker by hand. The cross-linking is responsible for the rigidity of the slime. The
amount of cross-linking is light compared to natural rubber in which sulfur forms numerous cross-links
between the polymer chains locking it into a very rigid structure.
6. Viscoelastic gels have characteristics of both liquids and solids. Note the new physical properties of the
cross-linked product compared to the properties of the original PVA solution.
Safety
Although these materials are relatively non-toxic, the Slime must not be ingested.
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Testing the Material and Reporting the Findings
Once you have made your Slime, observe its characteristics and behavior. For this lab, you must make at least
15 observations about your product. These observations can be simple and include things like color and
texture. They can also be more detailed, perhaps comparing them to the properties of solids, liquids and gases
(Does your Slime have constant volume? Does it have constant shape?) or to the original materials that went
into it. Observations can also include what happens when you manipulate it. For example, some common tests
for materials include the following:
1. Tensioning: Try stretching the material. Stretch it slowly. Then stretch it quickly. Describe the response on
the Data and Results page. In Material Science, this test is known as tensioning. The force applied is called
tensile stress and the amount of stretch induced is called the tensile strain.
2. Shear: Lay the material on the table and press down on top of it. Report the results. This is testing shear
which is the resistance of a material to deformation when a force is applied parallel to the surface on which
the object is resting.
3. Creep: Incline the material on a board and see how it moves. Report the results. This is known as Creep
which is the slow change of shape of the material by flow when it is subjected to a constant force such as
gravity.
4. Impact Strength: Roll the gel into a ball and throw it straight down against the table. Report your results.
This activity demonstrates Impact Strength and it is a measure of the resistance of a material to breakage.
Note anything else about the material that might help characterize it.
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Name: ____________________________________________Date: _______________ Section: __________
SLIME – Observations of a Polymer
Pre-Lab Questions
1. Watch videos on the use of the balance, Bunsen burner and glassware.
2. Choose an object on your desk or in your study area or backpack. Make 8 observations about this object.
3. Choose an object from your pantry or refrigerator, from the supermarket, or from a restaurant. Make 12
observations about this object.
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Name: ___________________________________________Date: _______________ Section: __________
SLIME – Observations of a Polymer
Observations and Results
Observations
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Observations (continued)
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