Acid and Base Experiment-Turmeric pH Indicator

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Acid and Base Experiment – Turmeric pH Indicator Painting

In this post, we will explore the use of natural pH indicators in this acid and base experiment. It is a fun STEM activity to help children learning about pH and how indicators work.  

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What is pH, acids and bases – Explanation for older children

The pH measures the acidity or alkalinity (basic) of a substance. Anything below 7 on the pH scale is acidic, and anything above is alkaline (basic). The pH measures the presence or absence of hydrogen ions. Acids and bases are created by the presence of charged ions (H+ or OH-) that help make up the chemical. Acids have hydrogen ions (H+), and bases have hydroxide ions (OH-). The higher the concentration of these ions, the stronger the acid or the base. When an acid and base combine, a chemical reaction occurs. They neutralize one another by breaking apart and reforming into new substances. Each time this happens, water (H2O) and salt forms. 

What you need to make Turmeric and other types of pH Indicator paper

• Card Paper
• Metal or plastic tray (preferably just larger than a piece of paper)
• Beetroot (plain or jarred), purple cabbage or turmeric
• Drying rack
• Paper towels
• Paintbrushes or q-tips (cotton buds)
• Cups or cupcake tin to put substances in
• household items that are acidic or alkaline- see list below for ideas

To do pH painting, you will need some traditional goldenrod paper (you can buy from some science sites, or you can make it yourself) or paper stained with cabbage juice, beetroot juice or the juice of another pH indicator.

To make homemade goldenrod paper, see my post, Sun Art for Kids and Toddlers which has instructions on how to do this. You can also use it for making sun prints in the summer.

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How to make beetroot, cabbage or turmeric pH indicator paper

To make beetroot juice, you can use beetroot from a jar (traditional polish pickled beetroot). You could also lightly boil a beetroot until it is soft enough to blend. Next, use a blender or hand blender until it turns to liquid. You can use the juice the way it is, or you may want to pour it through a strainer.

To make cabbage juice, rip up 5-10 cabbage leaves and place them into a blender. Blend them until it becomes a liquid. You can strain them or leave it the way it is.

Pour the beetroot juice or cabbage juice into a metal or plastic tray that is just larger than a piece of paper. It should be about 1 or more centimetres deep. 

Alternatively, you can cut the paper down into smaller pieces and use a smaller tray or plate.

Place the paper card into the tray and completely submerge it. Turn it over and let it soak until it looks completely and evenly saturated. Then carefully pull it out and allow as much liquid drain off into the tray as possible. Place it on a plate or rack to let it dry (it may take 30 minutes to an hour depending on the climate). Repeat for as many pieces of paper that you would like to make.

Indicator chemical reaction painting – Acid and base experiment

You can use a range of different substances to make indicator paintings. You can choose things from around your house. Be careful when selecting materials and make sure they are safe for your child and that two substances together won’t cause a dangerous reaction.

• Milk
• Lemon juice
• Milk
• Apple juice
• Orange juice
• Baking soda (mixed with water)
• Soda
• Antacid (mixed in water)
• Hand soap
• Detergent
• Shampoo
• Vinegar
• Window cleaner
• More…

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You can put several of these substances in small containers such as small cups or cupcake tins. Use q-tips, etc. to paint the beetroot or cabbage paper. You will need different q-tips for each substance you use (as some may react if combined). Children can also paint on turmeric (goldenrod paper) though it will only change colour in the presence of alkaline substances.  

Children will find that the paper changes colours as they paint them with different substances. It may take a few seconds or several minutes for the colours to develop.

The goldenrod (turmeric dyed) paper works particularly well. 

My son also enjoyed painting it with baking soda water and then going back over it with vinegar. Using both baking soda and vinegar causes the paper to change back and forth between yellow and red.

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Questions to ask – Acid and base experiment

• What do you notice?
• What happened? What do you think happened?
• What happens when you put the different substances on the paper? Do you notice any difference between the various pieces of paper (if you’re using different ones)?
• What did you learn?
• Is there anything more you would like to try or test?
• Do you have any questions? Can you design an experiment to answer one of the questions? 

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What they get from it

This hands-on activity will allow them to predict, observe, record and discuss, or present their findings. Doing experiments is an opportunity for children to make marks and write. They can also record their observations notes. Children enjoy doing investigations, and it can be highly motivational to write, even for more reluctant writers.

Research shows that people learn best (for long-term memory at least) when they learn through practical, hands-on experiences. (Ferri, B.H., Ferri, A.A., Majerich, D.M., Madden, A.G., 2016; Hearns, Miller & Nelson, 2009; Hillman, 2011). Younger children won’t be able to understand the more complex aspects of this activity/experiment. However, they will still have the opportunity to predict, observe, discuss and explain what they did and what they found. The more opportunities that children to explore, experiment and practice these skills, the more they will be able to develop scientific skills and thinking.

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Take it further

You may want to see some of the other fun pH experiments such as turmeric pH Indicator Experiment, Frozen Bicarbonate of Soda and Vinegar Experiment, or Color pH Baking Soda and Vinegar Science Experiment. These experiments can help children learn about chemical reactions as well as pH. 

It can be great for children to create experiments. You may want to allow them to ask questions to extend their learning. Ask them questions such as: What questions do you have about these reactions? Is there anything else you would like to know? Can you design an experiment to answer one of the questions?

For example, they might want to see if a frozen baking soda ball reacts faster with vinegar than dried baking soda ball. They may want to see if they can find the exact amount of vinegar to make the baking soda react. Alternatively, they may want to see if there is a difference in reaction between vinegar and citric acid. 

You may even try doing an electrochemistry experiment with goldenrod paper. Some science stores sell kits so that you can do colour changing experiments similar to the one above but using electricity rather than baking soda.

References

Ferri, B.H., Ferri, A.A., Majerich, D.M., Madden, A.G. (2016). Effects of In-Class Hands-On Laboratories in a Large Enrollment, Multiple Section Blended Linear Circuits Course. Advances in Engineering Education, 5 (3). https://files.eric.ed.gov/fulltext/EJ1121997.pdf

Hearns, M.K., Miller, B.K. and Nelson, D.L. (2009). Hands-On Learning versus Learning by Demonstration at Three Recall Points in University Students. OTJR: Occupation, Participation and Health, 30 (4), 169-171. https://journals.sagepub.com/doi/10.3928/15394492-20090825-01

Hillman, C.N. (2011). The effects of hands-on learning versus learning by demonstration on memory in community dwelling older adults (Doctoral dissertation, The University of Toledo). Retrieved from https://pdfs.semanticscholar.org/6231/d55fc1c730ec086f012677c54141f466e18e.pdf