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Major Concepts
Safety
Criteria for Glüg
Answers to Pre-Lab Questions
Materials and Apparatus
Suggestions for Advance Preparation
Anticipated Results
Extension Options
Assessment Rubrics
Relevant National Science Education Standards

Major Concepts

Borax (sodium borate decahydrate, Na₂B₄O₇^.10 H₂O) can be used to crosslink chains of the polymer (polyvinyl alcohol) found in white glue. The resulting product is a network of crosslinked chains that have rubber-like properties. The more borax that is used, the more crosslinks are produced until no more crosslinks can occur, stoichiometrically. The texture of the sample will then be grainy due to excess borax. Discussions can include concept of hydrogen bonding, viscosity, and crosslinking.

Level	Appropriate for students at basic, general, and honors levels.
Expected Student Background	The students should understand chemical bonding and how polymers are formed from monomers. The students should also understand the concept of hydrogen bonding and OH- groups.
Length of Time	2 days Day 1: 50 minutes to prepare the different samples (this is the amount of time it took to prepare 7 samples). Day 2: approximately 30 minutes to test and gather information on all the samples. Note: It is not necessary that the lab days are consecutive. The samples will keep their properties for at least a week and a half if kept in an air-tight container (zip lock sandwich bags work very well).

Safety

The students should be reminded of the importance of washing their hands at the conclusion of the laboratory exercise. Although the glue and borax are nontoxic, the samples are prepared using laboratory equipment that may have minute residues of other substances that are toxic. Reassure any student who gets the material on his or her clothes that it will wash out without a problem, but students need to use caution and not make a mess.

Criteria for Glüg and Expected Results of Pre-Lab Assignment

1. It should be tacky, but not sticky, grainy, or runny.

If a very small amount of borax (less than 1.0 grams) is used, not all the glue and borax will crosslink and the sample will either have excess liquid, or will be so runny that it is difficult to hold (this is runny). When too little borax is used (1.5–3.5 grams), the sample will stick to the students' fingers and small pieces will remain stuck to their fingers until they remove them (this is sticky). If too much borax is used (15 grams or more), there will be an excess amount of borax, and the sample will feel grainy due to the undissolved borax. This can be noticed on the first day (this is grainy). A good sample of Glüg should not have small pieces break off and stick to fingers. The sample should remain whole (this is tacky).

Answers to Pre-Lab

The students should be specific about the explanation of crosslinking. They should also provide an explanation of why they chose the amounts of borax they intend to use for their samples. They should conclude that they chose a variety to ensure a broad range of choices. See the Assessment Rubrics for a suggested grading guide.

Materials and Apparatus for Laboratory Activity Per Group

(for 7 samples)

Day 1:

White glue*
Powdered borax (amount depends on the individual group)
Balance (triple beam or electronic)
Zip lock plastic bags (for storage)*
1 Baby food jar (or a jar with a lid)
1 Marker to label bags
1 10 ml graduated cylinder
1 50 ml graduated cylinder
1 Spatula or Popsicle stick
1 50 ml beaker (to use for mixing the borax and water)
Water*

*Amount depends on the number of samples the students intend to make.

Day 2:

Samples from Day 1
5 feet of aluminum foil (to stretch the samples on)

Suggestions for Advance Preparation

• Make up several samples of Glüg prior to class, but do not tell the students how much borax is in each sample. Show students what is meant by each of the different criteria (show them the difference between sticky and tacky, etc.)

• Have all materials out for students to pick up.

• Make sure each group has enough glue (one small bottle of glue is more than enough for one group).

• Have the aluminum foil pre-cut for the students to use. (The aluminum foil may be used in different class periods. It is used to prevent the students picking up any residues on the lab bench. Also, the Glüg samples easily roll into balls on the aluminum foil.)

Anticipated Student Results and Answers to Questions

Please note that these are only example answers, student answers will vary. See the Assessment Rubrics for a suggested grading guide.

1. Create a table to organize all your experimental data. Be sure to include results to describe the criteria of the Glüg.

   (Note: You may choose to create a table for the students and allow them to fill in the spaces therein.)

   Answer:

   Table 1: Data Recordings

   amount of water	amount of glue	amount of borax	excess water	texture* (day 1)	texture* (day 2)	rank for ability to stretch
   30 ml	15.0 g	< 1.0 g	yes	runny	runny	5 (tie)**
   30 ml	15.2 g	1.0-2.0 g	yes	sticky	sticky (but less)	4
   30 ml	15.0 g	2.0-4.0 g	no	sticky	sticky/tacky	2
   30 ml	15.1 g	4.0-8.0 g	no	tacky	tacky	1
   30 ml	15.0 g	8.0-11.0 g	no	tacky	tacky but stiff	3
   30 ml	15.1 g	> 11.0 g	no	grainy	grainy	5 (tie)***

   *Texture: tacky, sticky, runny, or grainy.

   **Is too runny to stretch without making a mess.

   ***Is very difficult to stretch without breaking the sample.

2. Which sample had the best shelf life? (Which sample maintained its properties the best?)
   Answer: The sample containing 6.0 grams of borax, 30 ml of water, and 15.0 grams of glue maintained its properties very well; however, all the samples maintained their properties well. Changes were more noticeable in the samples using very little (less than 1.0 grams) or too much (greater than 11.0 grams) borax because the samples tended to dry out slightly.

3. Which sample stretched the farthest without breaking?
   Answer: Approximately 6.0 grams of borax, 30 ml water, and 15 grams of glue.

4. Which sample had the best texture (tacky not sticky, runny, or grainy)?
   Answer: Approximately 6.0 grams, 30 ml water, and 15 grams of glue.

5. Write a report for the board of directors to describe which sample of Glüg met the criteria best. This report should describe in detail the properties of the final product as well as your methods for determining the final results. Also, discuss how well your plan worked and any changes you had to make. You must also include a plan to make the product reproducible. The factory will need to make your product; do you think this is possible?
   Answer: The student report should include thorough details of the best final product and how that sample was chosen.

Answer the following questions based on what you learned from this experiment. Assume that amounts of glue and water are kept constant.

6. As the amount of borax is increased, what will happen to the texture and consistency of the polymer being made? Why?
   Answer: The crosslinking of the polymer by the B(OH^-)₄ will increase and the samples will become more rubber-like and more viscous.

7. Do you think a point can be reached where more borax will no longer affect the properties of the polymer (if water and glue were kept constant)? If such a point can be reached, what will happen to the consistency and texture of each sample?
   Answer: Yes, a point will be reached where no more crosslinking can take place and the borax will not dissolve or be used in the Glüg sample. The undissolved borax will give the Glüg a grainy texture. The sample will be very viscous and will be difficult to stretch.

Extension Options

Discussion on limiting reagents:

This experiment can show how too little borax limits the number of crosslinks that in turn affects the consistency and texture of the sample. Also, when too much borax is used, the glue and the water become the limiting reagent and it is obvious because theleft over borax gives the sample a grainy texture.

This lab is inquiry based. If you desire to have a more procedural based lab activity, below is an addition to the scenario and a procedure that may be cut and pasted into the student version of the lab. There is also a blank table for the students to use if you desire.

Procedure - Day 1

1. Label each of the zip lock sandwich bags with the amount of borax used for the sample that will be stored in that bag. (There should be at least five.)

2. Using a balance, weigh 15.0 grams of white glue in the baby food jar.

3. Measure 10 ml of water in a graduated cylinder and add to the glue in the baby food jar.

4. Place the lid on the jar and shake until the glue and the water are well mixed.

5. Using a balance, weigh the amount of borax that you and your team have chosen for the sample. (Remember that you need to have at least five samples with different amounts of borax in each.)

6. Place the borax into a 50 ml beaker and add 20 ml of water. Stir this and add quickly to the glue and water solution in the baby food jar.

7. Once the borax solution has been added to the glue and water, quickly place the lid on the jar and shake vigorously for 30–45 seconds.
   Note: This step must be done very quickly. If the mixture is not shaken immediately after the borax has been added to the glue, the crosslinking will not disperse evenly throughout the mixture.

8. Remove the sample of Glüg from the baby food jar and place into the appropriate zip lock sandwich bag.

9. Be sure to note if the sample is tacky, sticky, or runny and if there is any excess water.

Procedure - Day 2

1. Spread out a 5-foot long piece of aluminum foil on the lab bench.

2. Remove a sample from its bag and slowly stretch the sample to its breaking point.
   Note: This must be done very slowly or the sample will break prematurely.

3. Note the texture and consistency of each sample and evaluate its appropriateness for Glüg. In other words, does it meet the criteria?

4. Once each sample has been stretched, compare the lengths of each stretched sample.

5. Return each sample to its bag and discard according to your teacher's instructions.

Assessment Rubrics

Pre-Lab

Points	5	4	3	2	1	0
Background understanding	Plan addresses audience and explains all material in a clear and organized fashion.	Plan addresses audience and explains most material clearly.	Plan addresses audience and explains most material.	Plan addresses audience and explains some material.	Plan does not address audience and has little explanation.	Plan has no explanation of material.
Sample plan	Plan describes number of samples and amounts of all ingredients in each sample. It also clearly explains the reasoning for these choices.	Plan describes number of samples and amounts of all ingredients in each sample. It provides some reasoning.	Plan describes number of samples and amounts of all ingredients in each sample.	Plan describes number of samples and amounts of most ingredients in each sample.	Plan describes number of samples.	Plan has no explanation of reasoning or number of samples or amounts of ingredients therein.
Procedural plan	Plan describes in detail all steps for procedure clearly.	Plan describes in general most steps for procedure.	Plan describes some steps for procedure.	Plan has an overview of the procedure.	Plan has little description of the procedure.	Plan has no description of procedure.

Data Analysis

Points	5	4	3	2	1	0
Data table	Table is clear and easy to read. It displays all experimental data and all criteria set forth in "The Problem" (see student version).	Table is clear and easy to read. It displays all experimental data and most criteria set forth in "The Problem."	Table is clear and displays all experimental data and some of the criteria.	Table is clear and displays some experimental data and some of the criteria.	Table displays some data.	No table.
Questions 2,3, and 4	Answers all questions and all parts of questions clearly and provides explanation.	Answers all questions and all parts of each question clearly.	Answers all questions and but not all parts of each question.	Answers two questions.	Answers one question.	Does not answer questions.
Question 6	Answer is clear and concise and addresses all parts of the question thoroughly.	Answer is clear and concise and addresses all parts of the question.	Answer is clear and concise and addresses most of the question.	Answer is clear but only provides information for part of the question.	Answer is not clear and does not answer the question.	No answer.
Question 7	Answer is clear and concise and addresses all parts of the question thoroughly.	Answer is clear and concise and addresses all parts of the question.	Answer is clear and concise and addresses most of the question.	Answer is clear but only provides information for part of the question.	Answer is not clear and does not answer the question.	No answer.

Relevant National Science Education Standards

Unifying Concepts and Processes — The interworkings of the polymer and borax in the Glüg system are explored in this activity.

Science as Inquiry — The activity allows students to carry out their own scientific inquiry into how best to make Glüg.

Physical Science — The molecular and supramolecular structures involved in the Glüg system are central to the activity.

History and Nature of Science — The students experience firsthand how scientific knowledge is gained through experiment.

This activity was created by Stacy Brust.