Welcome campers and parents! My girls and I are excited to have you visit on the last day of “Weird Science” week at Summer Fun Camp 2013! My husband and I are both chemists, so as you can imagine, we are a very science focused family. The craft that we are sharing today rolls science and art together into one fun project. You will learn a little bit about acid-base chemistry while creating a beautiful “painting” on fabric.
Before we begin our craft, let’s talk about some of the science behind it.
What are acids and bases?
Acids and bases are two kinds of chemicals that you encounter everyday. The orange juice that you drank with breakfast contains citric acid. How did it taste? Sour, right? A sour taste is one characteristic property of acids. Vinegar, fruit juices, soda pop and tea are some other examples of foods that are acids. Bases, on the other hand, taste bitter. Many cough syrups taste unpleasant because their active ingredient is a base. (Of course you must never taste anything other than food because it could make you very sick.) Did you know that you are rubbing a base on your hands when you wash them with soap? Soap feels slippery on your skin, doesn’t it? That slippery feel is another characteristic property of bases. Bases also make great cleaning products because they dissolve oils and grease. Laundry detergent, dish soap and drain cleaner are all examples of bases that can be found in your home. When an acid and base are mixed together, they neutralize each other by reacting to form salt and water. If you have ever taken an antacid to calm a sour stomach, then you’ve experienced such a reaction. Antacid medications such as milk of magnesia are bases. When you ingest them, they neutralize some of the hydrochloric acid in your stomach to help you feel better.
What is pH?
While all acids and bases exhibit properties similar to those just discussed, they do so to varying degrees. Some acids are more acidic than others, and some bases are more basic than others. Scientists use the pH scale to describe how acidic or basic a substance is. Most acids and bases fall in the range of 0 to 14. Acids have a pH less than 7, becoming more acidic as the pH gets closer to 0. Bases have a pH greater than 7, becoming more basic as the pH gets closer to 14. A pH of 7 is called neutral, meaning it is neither acidic nor basic. Pure water has a neutral pH.
What are acid-base indicators?
Another property of acids and bases is their ability to cause color changes in certain dyes. These dyes are called acid-base indicators and they can be used as a quick visual test of pH. Many acid-base indicators can be found in nature. Probably the most well known, litmus, is a mixture of pigments extracted from lichens. It turns red in the presence of acid, blue in the presence of base, and is purple at neutral pH. Anthrocyanins are another kind of acid-base indicator found in plants such as blueberry, cornflowers, eggplant, and red cabbage. Today we will use red cabbage acid-base indicator in our artwork. We will dye a piece of fabric with red cabbage juice. Then we will apply acids and bases to the fabric to change its color. As these acids and bases diffuse through the fabric, the colors will blend together in a beautiful way that almost looks like tie-dye!
One more thing before we begin. There are a few simple rules you must remember to follow when working with chemicals.
- An adult must be supervising at all times.
- Always wear safety goggles to protect your eyes.
- Do not put anything in your mouth. This includes chewing gum and any food you might be snacking on.
Are you ready for some Weird Science? Grab your lab coat and safety goggles and let’s get to work!
- small red cabbage
- distilled water (optional)
- fine mesh strainer
- white, 100% cotton fabric (washed in water only, no detergent)
- lemon juice
- apple juice
- dish soap
- baking soda
- Arm & Hammer Super Washing Soda (optional/not recommended for young children)
- plastic cups
- a tarp or sheet of plastic
- safety goggles
To prepare the red cabbage indicator, chop a small red cabbage into 1 inch chunks. Place the cabbage cubes in a blender and add enough distilled water to just cover the cabbage. (You can use tap water instead of distilled. However, depending on your water supply, your indicator may produce a slightly different range of colors.) Blend on the puree setting for at least 30 seconds. Then let the cabbage and water mixture sit for 10 minutes before straining it into a bowl. Gently press the cabbage with the back of a spoon to speed up the straining. The purple juice in the bowl is your acid-base indicator. At this point, you may want to move your cabbage juice outside. I am sure you have noticed how horribly smelly it is! Soak your fabric in the cabbage juice indicator for about half an hour. Squeeze out the fabric just enough that it is no longer dripping and hang it to dry. Tiny bits of cabbage that are stuck to the fabric will easily brush off when it is dry. Do not rinse the fabric because you will wash away the indicator. Prepare your acids and bases while waiting for the fabric to dry. Lemon juice and apple juice can be used as-is. Dilute the dish soap about 1:1 with water. Dissolve 1 tablespoon of baking soda in 1 cup of water. Washing soda can be irritating to the skin if you spill it on yourself. This is the reason why I make it optional. I’ll leave it up to the parents to determine if it is appropriate for their child. If you do decide to use the washing soda, dissolve 1 tablespoon in 1 cup of water. Lay the cabbage juice dyed fabric on a tarp or sheet of plastic to protect your work surface. Now the fun begins! Use eyedroppers to apply the acids and bases to the fabric. Lemon juice is the most acidic and has a pH of about 2. It turns the fabric bright pink. Apple juice has an acidic pH in the range of 3.5 – 4.5 and turns the fabric violet. The baking soda solution is basic, with a pH of 8, and it turns the fabric blue. Dish soap has a pH near 9 and turns the fabric blue-green. The washing soda solution is the most basic with a pH of 11.5. It turns the fabric yellow-green. Try placing drops of acid and base right next to each other and observe what happens to the color of the fabric where they mix together. You don’t get the color you would expect if you were mixing paint. Do you know why this happens? Continue adding drops of acids and bases until the fabric is covered. Hang your artwork to dry. Aren’t they pretty? My girls had so much fun that they are already asking when we will do it again!
Note: The design is not colorfast, so you cannot get it wet or display it in a humid environment. Treat it like a watercolor painting and it will stay beautiful!
Take it further: As an additional activity, look around your kitchen for other substances that might be acids or bases. Predict whether they are acidic, basic, or neutral, and what color they will turn your red cabbage indicator fabric. Then test them out. Some suggestions: Vinegar, milk, carbonated soda, tea, glass cleaner, and laundry detergent.
Thank you for stopping by today! We hope you had fun and would love to see photos of your acid-base indicator artwork on the Summer Fun Camp facebook page! If you have any questions about the chemistry we did today, please comment or send me an email.