Each session is timed for approximately one hour. Although I have written these sessions while trying to maximize student involvement, I have found that it is also feasible for the teacher to do the demonstration one day (or have it prerecorded) and have students make the playdough the next day. By planning each session to be about one hour, I anticipate you can adapt it to your schedule.
Session 1: Begin by introducing the role of a chemical engineer. There are several YouTube videos available on the subject that are student friendly. Then take out and show them a fresh can of Play-Doh. Discuss how chemical engineers wanted to create a fun type of clay for kids to play with that was soft, stretchy, and strong enough to mold into shapes. They also wanted it to be easy to extrude, or squeeze through, molding machines that could make shapes, grow Play-Doh hair in plastic figures, mold pretend food, etc.… Showing an old Play-doh commercial would be appropriate here.
After about 15 minutes of the above introduction, demonstrate making a batch of playdough from flour, water, and salt. Use my favorite recipe, mentioned earlier in the unit, but do not add the cream of tartar or oil yet. Those will be saved for future experiments. You will also be modeling how to weigh your ingredients on the scale. Stress making careful measurements. After the demonstration, which should take 15 minutes, have students work in small groups or pairs to make a batch just like you demonstrated. If you prepare materials in advance, it should take them 30 minutes to make their own batch. Record the ingredients used (including measurements) on chart paper for batch 1. I recommend making these student batches the same color. It will be easier to compare them to other batches and students will get a chance to choose their own color later in the unit. Label and save each student product in a plastic bag.
Session 2: Compare saved playdough to store bought Play-Doh. Discuss that materials have properties that we can use to describe them. Play-Doh is soft, stretchy, cool to the touch, smells nice, can be sticky, dry, or brittle when dried out. Set a goal to make the perfect playdough. Develop a rubric together based on important characteristics such as texture, elasticity, stickiness, etc.… It should look something like this:
Batch #
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Sticky
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Stretchy
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Soft
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Able to make shapes
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Overall rating
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1
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Very Sticky
A Little Sticky
Not Sticky
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Very Stretchy
A Little Stretchy
Not Stretchy
|
Very Soft
A Little Soft
Not Soft
|
Yes
No
|
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2
|
|
|
|
|
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3
|
|
|
|
|
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4
|
|
|
|
|
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5
|
|
|
|
|
|
Demonstrate a second batch, using a different color, but this one includes added oil. During the demonstration, discuss the definition of molecules and how the oil shortens the molecule chain, making the dough a little less stretchy, but also helps retain moisture and slows the drying out process. As before, have students replicate your example. Save the final product in labeled plastic bags. Update the chart paper for batch 2, and add scores based on the rubric for the first two batches made.
Session 3: In this session, discuss how scientists feel it is important to track their progress and record results. Now that students have made two batches of play dough, we need to record the step in our own notebook. Refer to the chart paper you have recorded notes on in class. Students can create their own note format, or you can create a copy for them. It should look something like this:
Batch #
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Amount of flour
|
Amount of salt
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Amount of water
|
Amount of oil
|
Amount of Cream of Tartar
|
Notes
|
1
|
200 g
|
100 g
|
200 g
|
0
|
0
|
|
2
|
200 g
|
100 g
|
200 g
|
10 g
|
0
|
|
3
|
200 g
|
100 g
|
200 g
|
10 g
|
10 g
|
|
4
|
|
|
|
|
|
|
5
|
|
|
|
|
|
|
Once the notebooks are updates, continue with your 3rd batch – this time adding Cream of Tartar. Explain that Cream of Tartar is slightly acidic, and because of this, it affects the gluten structure of the dough to make it more elastic. Tartaric acid acts as an emulsifier, so it helps prevent any added oil from separating. It also prevents the salt from crystalizing, resulting in a smoother, softer playdough.
As before, have students make batch 3 with added oil and Cream of Tartar and record their ingredients used and rate the final product according to the class rubric.
Sessions 4 and 5: The last two sessions are for students to make 2 or more additional batches of playdough but allow them to modify one ingredient at a time. For example, they may elect to use 50 g of salt instead of 100 g, but all other ingredients remain the same. My advice is to have students work in pairs and decide on the modified ingredient as a class. Then have each pair of students follow the same recipe. This is a good time to emphasize the scientific methodology of having only one variable in an experiment and repeating the experiment several times. Be open to different ideas (within reason). Maybe students will want to try a different type of flour or oil instead of modifying the amount of an ingredient. Whatever they decide, the ingredients and rating should be included in their notebooks.
During these sessions, it may be interesting to model the gluten extraction as detailed in the beginning of the teaching strategies section of this unit. It does take about 15 minutes, so doing a live demonstration may not be appropriate if students are eager to work. I recommend introducing the idea live, then have a recording of the process to show, followed by a chance to see the extracted gluten ball in person. It will keep for a few days but trust me – if you leave it out too long (more than a few days without refrigeration) it will rot and smell horrible!
Students at this age will learn the role of a chemical engineer and how to conduct and record experiments by doing the activities. To teach chemistry concepts, I recommend integrating discussions about mixtures and solutions, atoms, and molecules in addition to the chemistry of gluten and starch that is related to dough. Much of the content provided in the background information can be taught to students through discourse as they are discussing how to make playdough.
I initially taught this lesson to 2nd grade students, and once we had perfected a recipe for playdough, I had a small group take on the challenge of providing playdough to the play-based learning centers in our kindergarten classes. My group of students took orders from the kindergarten students and were thrilled to deliver the playdough they made to the kindergarten classes. I also gave my students a copy of the recipe to take home, and many excitedly reported making their own batches of playdough at home.