Materials Included In Kit

Additional Materials Required

Safety Precautions

Warn students not to ingest the material and to use it only for the purposes intended. Do not allow slime to remain on clothing, upholstery, carpet or wood surfaces. Slime will stain many surfaces. Clean up any slime as soon as possible. There are no known toxic effects produced by sodium borate, PVA, or the slime; however, students should wash their hands thoroughly after handling the slime. Please consult current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures governing the disposal of laboratory waste. The gelled slime and leftover polyvinyl alcohol solution will last two days to a week, at which time they may start to mold. Both may be disposed of in the solid waste disposal or by flushing them down the drain with plenty of water according to Flinn Suggested Disposal Method #26. Leftover sodium borate solution may be saved for later use or rinsed down the drain with plenty of water. Dispose of the cups and wood sticks in a waste container.

Lab Hints

• This kit contains enough materials for 30 students working individually or 60 students working in pairs—enough to make at least 30 good-sized batches of slime.
• On prolonged storage, the slime may develop colonies of mold or microorganisms. It should be discarded when this occurs for both health and aesthetic reasons.
• Discretion as to whether to allow students to take the gel out of the classroom is up to the individual teacher. Warn students not to allow young children or pets to ingest the material. Also caution students not to leave the slime in a place where it may accidently be ingested
• If food coloring is used in the slime, the slime will stain any surface with which it comes in contact.

Answers to Questions

1. Observe and record the physical properties of slime.

   Liquid- and solid-like; elastic; wet; smooth; thick; gel; slimey; no odor.

2. Knead the slime into an elastic, semi-rigid mass or ball. Hold a small part of the ball and watch it flow and stretch without breaking. Try stretching and pulling the slime quickly. What happens? Can you mold the slime back together into one piece?

   If pulled abruptly, the slime will break. Chunks of the mechanically broken gel can be reworked into a single mass.

3. Place the gel back into the cup. What do you observe? Place the slime onto the table. What happens to its shape? Record observations.

   When placed in a cup, the gel assumes the shape of the container. When placed onto the table, it flows to form a film.

4. Break off a small piece of the slime and place it into a cup of water. What do you observe?

   When placed into water, the gelling process reverses and the slime becomes liquid-like.

5. Draw a picture or write your name on a piece of paper with a water-soluble marker. Press the ball of slime onto the paper for only a split second, as the slime will stick to the paper if left on too long. What happens? Repeat, this time writing your name backwards. What do you observe this time?

   When the slime is placed onto the ink, the mirror image of the design will be lifted and transferred to the slime. When the slime is placed onto the backwards design, the design is transferred to the gel and reads forwards.

6. What other physical properties of the slime do you observe? Record these.

   Student answers will vary.

7. What other experiments can you perform to test the properties of slime? Describe the experiments.

   Student answers will vary.

References

Cassasa, E. Z.; Sarquis, A. M.; Van Dyke, C. H. J. Chem Ed. 1986, 63, 57.

Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; University of Wisconsin Press: Madison; 1989; Vol. 3, pp 362–363.

Introduction

You’ll have a “slimey” good time with this laboratory! Simply mix two clear, colorless solutions together and watch the mixture instantly gel into a smooth, viscous, elastic ball of slime.

Concepts

• Polymers
• Hydrogen bonding

Background

Slime can be made by following a variety of different recipes. One very popular recipe, which will be used in this activity, involves the combination of aqueous solutions of polyvinyl alcohol and sodium borate. After preparing a cross-linked polyvinyl alcohol-borate gel, you can make observations of the interesting properties of the slime.

Polyvinyl alcohol, PVA [–CH₂CH(OH)–]_n, is the world’s largest volume, synthetic, water-soluble polymer. PVA is considered non-hazardous and is used in many adhesives, films, and elastomers. Its most popular use in schools is in the preparation of “slime.” PVA is a linear polymer with a repeating vinyl alcohol unit (see Figure 1). Its molecular weight can range from 25,000 to 300,000.

Sodium borate decahydrate, Na₂B₄O₇ 10H₂O, when dissolved in water, hydrolyzes to form a borate ion-boric acid buffer with a pH of around 9 according to Equation 1 The equilibrium reaction between boric acid and the borate ion is represented by Equation 2 The borate ion is tetra-functional in its interaction with alcohol (–OH) groups, having four bonding sites, and is particularly effective in creating three-dimensional gel networks from polyvinyl alcohol or gums, such as guar gum. The chemistry by which a cross-linked polymer gel is produced from linear polymer molecules is quite straightforward. When solutions of PVA and sodium borate are mixed in an approximately ten-to-one ratio, the borate ions react with the hydroxyl (–OH) groups of the long-chain polyvinyl alcohol molecule. Figure 2 shows the cross-linked polyvinyl alcohol-borate gel. The figure, while oversimplified, if extended into space and in three dimensions, may help in visualizing the polymer network. The structure indicates how hydrogen bonding interactions might figure in a cross-linked yet labile network. This structure accounts for the physical properties of slime—the gel is elastic and fluid-like, not stiff or hard; the gelation process will completely reverse if the slime is placed into water; and simply the fact that such a high molecular weight polymer is completely soluble in water. Note that there is much space within the gel—most of this space is taken up by water molecules of the solvent; hence, slime is composed of about 96% water. Figure 2 implies covalent bonds connecting the oxygen and carbon atoms. It should be realized that the bonds connecting oxygen to carbon are weak cross-links or interactions and not strong covalent bonds. Weak crosslinking within the polymer occurs, resulting in the three-dimensional structure (network) of connected chains. When the concentration of cross-linked chains is high, the solvent is, to a large extent, immobilized within the network and a semi-solid gel results. Thus a visco-elastic (viscous and elastic) gel with interesting properties results. Other examples of cross-linked networks and gels are rubber, gelatin, fruit jellies, agar media, tofu and yogurt.

Materials

Safety Precautions

Do not ingest the material and use it only for the purposes intended. Do not allow slime to remain on clothing, upholstery, carpet or wood surfaces. Slime, if colored with food coloring, will stain many surfaces. Clean up any slime as soon as possible. There are no known toxic effects produced by sodium borate, PVA, or the slime; however, wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

Part 1. Preparation of Slime

1. Measure 50 mL of 4% polyvinyl alcohol solution and pour it into a plastic cup.
2. Add a few drops of food coloring, if desired, and stir with a wood stick.
3. Measure 5 mL of 4% sodium borate solution.
4. Slowly and with constant stirring, add the sodium borate solution to the cup containing the polyvinyl alcohol solution. The mixture will gel almost immediately, but keep stirring until the mixture has a smooth consistency.

Part 2. Analysis of Slime—Record observations on a separate sheet of paper after performing each test.

1. Observe and record the physical properties of slime.
2. Knead the slime into an elastic, semi-rigid mass or ball. Hold a small part of the ball and watch it flow and stretch without breaking. Try stretching and pulling the slime quickly. What happens? Can you mold the slime back together into one piece?
3. Place the gel back into the cup. What do you observe? Place the slime onto the table. What happens to its shape? Record observations.
4. Break off a small piece of the slime and place it into a cup of water. What do you observe?
5. Draw a picture or write your name on a piece of paper with a water-soluble marker. Press the ball of slime onto the paper for only a split second, as the slime will stick to the paper if left on too long. What happens? Repeat, this time writing your name backwards. What do you observe?
6. What other physical properties of the slime do you observe? Record these.
7. What other experiments can you perform to test the properties of slime? Describe the experiments.

Part 3. Disposal of Slime

The slime will last two days to a week. Store it in an airtight, zipper lock plastic bag. When the slime starts to mold or lose its consistency, dispose of it in an appropriate waste container. Dispose of the cups and wood sticks in a waste container.