Today we are sharing one of our most popular activities from our Parent-Daughter STEM Workshops. These would make a great gift for friends or family and you will impress everyone when you teach them the chemistry behind how it works!
Background:
While you may have made or used bath balls before, have you ever stopped to think about what makes it fizz? This reaction is known as acid-base chemistry. Baking soda, or sodium bicarbonate, is a base which means its pH is higher than 7. Citric acid is an acid which means its pH is lower than 7. When an acid is mixed with a base, a reaction occurs as the two chemicals try to neutralize each other (get to a pH of 7). You need one more chemical to make this reaction start: water! The dry baking soda and citric acid don’t react with each other until they become wet. That’s why you see a small amount of fizz when you make the bath ball but the big fizz is saved for when you drop it into the bath. In this experiment, the acid-base reaction produces carbon dioxide gas which makes the fizzy bubbles.
Have you ever thought about what makes a bath ball smell nice? Those scents are made of volatile small molecules that are extracted and isolated by a chemical process. Each scent is made of a unique chemical structure. The smell of lavender is a combination of four small molecules while wild orange is a single molecule.
Materials:
Dry Ingredients:
- 1 C baking soda
- 1/2 C citric acid
- 1/2 C Epsom salt
- 1/2 C corn starch
Liquid Ingredients:
- 4 Tbsp olive oil (or other oil of your choice)
- 2 tsp water
- Several drops of essential oil (optional)
Other materials:
- Flower molds or other shape of your choice (small disposable cups work great for making disks)
- Small bowl or cup
- Craft stick or spoon
- Measuring cups and spoons
Method:
- Combine the dry ingredients in a large bowl. (Note: while completely safe, citric acid can damage some counter tops including marble and granite so we suggest putting a place mat under your work.)
- Combine liquid ingredients in a small container with a lid. Shake well. (This is very important so if your liquid ingredients sit for a while, give them another good shake.)
- For the small flower molds, combine 1 Tbsp of the dry ingredients with 1/2 tsp of liquid ingredients in a small bowl or cup. (You can increase the amounts if of both ingredients if you are using larger molds).
- Stir with a spoon or craft stick. Hold the cup up to your ear and listen for the fizz. That’s the acid-base reaction starting!
- The mixture should be the consistency of crumbly sand (Picture 1). Add a little more liquid if needed but be sure its no too wet.
- Pour the mixture into your mold and press down with the back of a spoon or your fingers to pack it well (Picture 2).
- Let it dry overnight before removing from the mold.
- When you’re ready for a bath, drop a couple into the running water. Watch and listen as the reaction continues!
Picture 1 
Picture 2
We’d love to see pictures of the Fizzy Flowers you create! Email your pictures to info@stemlikeagirl.org to be featured on our website or social media. Or you can tag us on instagram @stemlikeagirl_pdx and use the hashtag #stemlikeagirlpdx
