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  • Our STEM projects are designed so that participants get it wrong before they get it right. You will observe your students struggling as they attempt to create their own STEM projects. This process is an empowering experience, building perseverance, frustration tolerance and growing overall confidence! With your support, students will step out of their comfort zones to think, build and problem-solve for themselves.
  • Productive Struggle Skills
    - Measuring ingredients accurately
    -Fitting mixture into molds

In this Rosie Labs guide you will find:

  • Productive struggle opportunities for students during their project build,
  • Lesson objectives and concept overview,
  • Optional STEM topic video to share with participants,
  • Step-by-step instructions and video of the Rosie Riveters’ Bath Bomb Project,
  • Optional STEM activities to further explore the objectives and concepts used in the project build.

Objective

Students will learn the differences between chemical and physical changes in matter while making bath bombs to take home!

Concept Overview and Experiment Inspiration

It may be surprising to find that chemical reactions are a part of daily life. Cooking, baking, rusting, and rotting are all forms of chemical reactions that we can see on a daily basis. A chemical reaction is a process a process that involves rearrangement of the molecular structure of a substance to turn it into something new. During this process, chemical bonds are broken and formed in order to create new molecules.

A chemical reaction can happen to anything. In fact, a reaction can occur between atoms, ions, molecules of a single element or compounds. The only important thing is that the result is a change in chemical identity (i.e. a new substance is formed). A common example of a chemical reaction is rust. When an object rusts iron (Fe) in the metal combines with oxygen (O2) in the atmosphere. Chemical bonds are created and destroyed, ultimately forming iron oxide (Fe2O3), a completely new substance. For comparison, a great example of a physical change is eating cereal in the morning.

This is different than a physical change where matter changes forms but not chemical identity. Some examples of physical changes are boiling, melting, freezing and shredding. A key difference between chemical and physical reactions is that physical reactions are technically reversible, whereas chemical reactions are not.  When you take dry cheerios and place them into milk you get a physical change. The cheerios become soggy, but if you let them dry out, they will reverse back to their original state.

A more difficult but important example is the evaporation or freezing of water. While you may think that is a chemical change, it is actually a physical change because a new substance is not formed (i.e. it is still water), it is just in a different physical state (freezing into a solid or evaporating into a gas). However, the composition of the water has stayed the same. 

Science Goals

  • A Physical Change is when matter changes in the appearance, smell, or presentation without changing the kind of matter in the substance
  • A Chemical Reaction is when a new kind of matter is created from combining reactants together

Vocabulary

Physical Change – when matter changes in the appearance, smell, or presentation without changing the kind of matter in the substance
Chemical Reaction – a process that involves rearrangement of the molecular structure of a substance
Reactant -a substance that takes part in and undergoes change during a reaction
Product– Something new that is made as a result of a chemical reaction

Required Materials

  • 1/2 cup baking soda
  • 1/4 cup citric acid
  • 1/4 cup corn starch
  • 1/2 tablespoons baby oil (any skin safe oil will work)
  • food coloring (optional)
  • bath bomb mold (cupcake tin, plastic egg, etc.)
  • bowl
  • spoon

Step-By-Step Instructions

Step 1

Combine 1/2 cup baking soda, 1/4 cup citric acid and 1/4 cup cornstarch together in a bowl.

Step 2

Mix the three ingredients well.

Step 3

Add food coloring as desired.

Step 4

Add 1/2 teaspoon of baby oil, just enough to moisten the mixture so that the powder sticks together. Add oil until the mixture holds it’s shape when pinched (it will still look powdery).

Step 5

Pre-prep the mold with baby oil and corn starch – similar to preparing a pan for baking.

Step 6

Scoop the mixture into a mold to form a shape

Step 7

Let the shapes dry overnight.

Optional STEM Activities

Resource 1

Now that you have created your bath bomb you can ask further questions.

  • Has the bath bomb made a chemical reaction yet? (no!)
  • What ingredient do you need to start the chemical reaction? (water!)
  • What are the reactants? (bath bomb and water)
  • What will the product be? (Carbon dioxide will form as bubbles or fizz in the water). 

Resource 2

Try another experiment to explore chemical reactions!

  • Put half a lemon into a cup, so that the rind is facing downwards
  • Place a spoonful of baking soda on top of the lemon.
  • Add a few drops of food coloring on top of the lemon and baking soda.
  • Take a popsicle stick and push the baking soda down into the lemon.
  • Note what happens when the citric acid from the lemon and baking soda mix and a chemical reaction takes place!

Resource 3

Advanced Exploration

Sometimes, in a chemical reaction, a third substance is used to speed up or slow down the rate of the reaction. A substance used to speed up a reaction is known as a catalyst and a substance used to slow down a reaction is known as an inhibitor. Unlike the other substances, the catalyst or inhibitor is not used up in the reaction to form the products; it simply changes the speed or gets the reaction going while maintaining its own structure. Some factors that can act as catalysts or inhibitors include temperature, other chemical compounds, or pressure.

Baking is a great example of a chemical reaction that uses a catalyst to form. When you mix all the ingredients of a cake together you get a wet batter. Once the batter is placed into the oven heat, the catalyst is applied which causes the batter to turn into a cake. The cake, once baked, cannot turn back into batter and has therefore undergone a chemical change. Further evidence of this chemical change can be seen in the tiny holes that form during the baking process. This is actually where carbon dioxide has been released from the cake, leaving small spaces where it once was.

Have students find a partner and review a cake recipe together. Students can work together to identify the physical changes and chemical reactions happening in the recipe. Identify concepts using vocabulary words: reactant, product, physical change, chemical reaction, catalyst, inhibitor. Discuss what they believe is happening during the baking process.

 

Resource 4

Further Exploration of Chemical Reactions

Discuss with students the six signs of a chemical reaction: Light, Heat, Gas Formation, Precipitate Forms (Liquid + Liquid = Solid), Change in Color and Bubbles. Can they give an example when they see these signs?

After discussing these categories have students choose a chemical reaction example and act them out in a small skit or demonstration for the class!

Advanced Exploration

Older students can do the same activity as above but they can start to look at the various types of chemical reactions more closely. Chemical reactions can be defined using the following six categories:

    1. Synthesis reaction: when two substances combine to make a new substance. Example: A + B ! AB (example: formation of salt Sodium + Chloride)
    2. Decomposition reaction: when a complex substance breaks down to form two separate substances. Example: AB ! A + B (Carbonated drinks – when carbonic acid in soft drinks breaks down and produces water and carbon dioxide after you open a soft drink)
    3. Combustion: when oxygen combines with another compound to form water and carbon dioxide (produces energy in the form of heat). Example: Oxygen + A ! H2O + CO2 (Burning of wood or a candle)
    4. Single displacement or substitute reaction: when one compound takes a substance from another compound. Example: A + BC ! AC + B (Formation of water – 2 Hydrogen and 1 Oxygen molecule; another example is rust)
    5. Double displacement or metathesis reaction: when two compounds trade substances. Example: AB + CD ! AC + BD (vinegar and baking soda)
    6. Photochemical reaction: when a chemical reaction involves photons from light. (photosynthesis)

 

Resource 5

Physical Change

A great way to contrast the chemical reaction concept is to explore physical changes with students. Introduce the states of matter, solid, liquid and gas by showing images of water, ice and steam. Explain how the molecules of the water stay the same but the water changes states when it changes temperature.