Color Changing Acid-Base Experiment

Every kid should have a chance to play the mad scientist at least once in their childhood. Chemistry, with its mixing of potions and unexpected results, is the perfect way to introduce science to young kids. This experiment is particularly appealing, because kids get to mix substances and solutions together and will likely be surprised by the color changes this mixing brings about.

Acid/Base Background

Nearly every liquid is either acidic or basic in nature. Acids are molecules that release hydrogen ions (H+) when dissolved in water. Bases release hydroxide ions (OH-). The pH scale is a way of measuring and precisely specifying how acidic or basic a solution is. Liquids with a pH between 0 and 7 are considered acidic, while liquids with a pH between 7 and 14 are considered basic.





Liquids, such as distilled water, with a pH of 7 are considered neutral. They are neither acidic nor basic, because they contain an equal concentration of hydrogen ions and hydroxide ions. If a liquid has a pH near 7, it is considered either a weak acid or a weak base, depending on which side of the scale it falls. In contrast, an acid with a pH near 0 is very strongly acidic and a base with a pH near 14 is very strongly basic. These substances are dangerous and can cause corrosion and burns.





So how do scientists know if a substance is an acid or a base? One way is using something called an indicator, which changes color depending on the pH of the substance it comes in contact with. The most widely known indicator is litmus paper which turns red in acidic solutions and blue in basic solutions. However, it is easy to make your own. One commonly used natural indicator is red cabbage juice. Another is turmeric, a spice found in the Indian food, curry.

In order to put together this experiment quickly and easily, I've used an indicator of turmeric and rubbing alcohol. This solution changes color from yellow-ish orange to dark red when in contact with bases. While the child will not be able to distinguish acids from neutral substances, if they add a substance to the turmeric indicator and it turns red, they will know that that substance is definitely a base.

Materials

• turmeric (we used 1 teaspoon)


• isopropyl (rubbing) alcohol (we used 1 cup)


• measuring glass or cup


• 1/2 or 1 tsp measuring spoon


• spoon for stirring


• empty glasses or clear plastic containers for observing reactions


• masking tape and marker to label containers

You will also need substances to test. We used:

• distilled water


• soap


• laundry detergent


• baking soda


• vinegar


• lemonade


• borax


• oxygen bleach

However, the possibilities are endless. Here are some other suggestions:

• orange juice


• tomato juice


• soda


• milk


• shampoo


• conditioner


• body wash


• dishwashing soap


• bar soap


• salt water


• chlorine bleach


• bubbles

Instruction

1. First, you need to make your indicator solution. Mix 1 cup of rubbing alcohol with 1 teaspoon of turmeric. (You can half or double the ingredients if you want more or less indicator.)
   
   
   
   


2. Next, label your glass or plastic containers with each of the solutions you want to test.


3. Divide your indicator solution between your test cups. Since we had 8 glasses, we put approximately 1 ounce of solution in each of our cups. (The exact amount is not important.)
   
   
   
   


4. Finally, allow your child to pour a small amount of each test substance in the corresponding labeled container. If the indicator solution starts to turn a deep red, the child will know the test substance is a base. If the solution does nothing, they will know it is either an acid or is neutral.
   
   
   
   


5. For added fun, your kids can add a little bit of acid (such as vinegar) to the solutions that they found to be basic. Like magic, they will change back to their original color!
   
   
   
   

Once you're all done, some kids will have an irresistible desire to mix all their "potions" together. I say let them! What better way to nurture budding scientific curiosity? 

(If you have them, pipettes make a great way to ensure the ensuing "science" doesn't get onto counter-tops and other surfaces. With my kids, pouring is often messy. Learning to use a pipette is a great fine motor control activity as well.) Have fun encouraging your young chemist!

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Michelle is a homeschooling mama of 3 young kiddos and a former engineer and research scientist. She blogs at Research Parent, an education-focused website featuring free printable learning material and activities for K-12. Follow along on Pinterest, Facebook, Instagram, and Twitter

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