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Usually on Wednesdays we feature Bug of the Week, so today's chemistry lesson is inspired by insects.

Dr. Thomas Eisner was a very curious man. He was particularly curious about insects, like the beetle shown in this video (has pop-up ad).

When he discovered these particular beetles, Dr. Eisner began to experiment with them because he wanted to know what and how they were squirting. One of the unexpected things he found out was that the temperature of the spray the beetle released was very hot, nearly 100° C. How could that be?

Endothermic and Exothermic Reactions

Sometimes chemical reactions between two or more substances give off or take in energy, often in the form of heat. In exothermic reactions, heat energy is given off during the reaction and the temperature increases. In endothermic reactions heat energy is removed by the reaction ("taken in") and the temperature of the reactants decreases.

Below are two chemical reactions that use household products. Find out whether they are exothermic or endothermic.

Notes:  These activities are messy fun, so perform them in a sink, tub, or outdoors in an area where wet spills are not a problem. Also, scientists never eat or drink their experiments!

Reaction 1.


  • About 26 g lemonade drink mix* (make sure the primary ingredient is citric acid)
  • Baking soda
  • Liquid measuring cup
  • 1/4 cup dry measuring cup
  • Water (room temperature)
  • Large Styrofoam cup (to help insulate the reaction)
  • Container (glass or cup) to mix the drink mix and water in
  • Thermometer or temperature probe
  • Spoon

* Math alert:  Originally I used Crystal Light pink lemonade mix, which came in 3.68 g packets (see the serving size information for the number of grams per packet). I used 7 packets for about 28 g. Then I switched to an off brand, and the packets were 2.6 g each (10 packets for 26 g). It worked just as well. Also, check the amount of vitamin C information on the labels. The raspberry-flavored lemonade mix contained significantly more citric acid for some reason.


Procedure 1:

  1. Measure 100 mL (approx. 1/3 cup) of room temperature water and pour into in a container.
  2. Add 26 g of drink mix into the water in the container. Stir until completely dissolved.
  3. Use the thermometer or probe to measure the temperature of the solution, taking care not to rest the thermometer or probe on the bottom or side of the cup.
  4. Measure 1/4 cup baking soda into the Styrofoam cup.
  5. In a sink or similar area, quickly add the drink mix solution to the baking soda in the Styrofoam cup.
  6. As the reaction starts to slow, take the temperature again. (You may want to let the children touch the solution and compare to the room temperature water. They will need to wash their hands afterwards.)

reaction 1 citric acid

Did the temperature of the contents of the Styrofoam cup  go up or down?

Reaction 2:


  • 2 teaspoons active yeast
  • Liquid measuring cup
  • Measuring teaspoon
  • Water at room temperature
  • Cup or similar container for mixing yeast
  • Large Styrofoam cup
  • Thermometer or temperature probe
  • Hydrogen peroxide (be sure to use 3 %, the kind sold for home use) - held at room temperature
  • Spoon

Procedure 2.

  1. Measure 100 mL of room temperature water (approx. 1/3 cup) and pour into the yeast-mix container.
  2. Mix the 2 teaspoons dry yeast into the water. Stir until thoroughly mixed.
  3. Take the temperature of the solution, taking care not to rest the thermometer on the bottom or side of the cup.
  4. Add 100 mL (about 1/3 cup) 3% hydrogen peroxide to the Styrofoam cup.
  5. Take the temperature of the hydrogen peroxide, taking care not to rest the thermometer on the bottom or side of the cup. The two solutions should be roughly the same temperature.
  6. In a sink or similar area, add the yeast solution to the hydrogen peroxide in the Styrofoam cup.
  7. As the reaction starts to slow, take the temperature again. (You may want to let the children touch the solution and compare to the room temperature water. They will need to wash their hands afterwards.)

Did the temperature go down or up?



Which reaction was endothermic? Which reaction was exothermic? Let us know what you find out.



If you are interested in learning more about the beetles, read the first chapter in:

For Love of Insects by Thomas Eisner


For more chemistry activities, check the Table of Contents for Chemistry Week page.



Each Tuesday we generally celebrate plants with "Seed of the Week" posts. Today we'll look at chemicals found in plants for Chemistry Week.

Plants contain an encyclopedia of different chemicals, which they use for growth, communication, and defense. For this lesson we are going to look at three different classes of plant chemicals that can be used to study the pH of acids and bases.

A Quick Introduction to Acids and Bases

People have known for centuries that acids:

  • Taste sour (like lemons)
  • Dissolve or corrode metals
  • Turn blue litmus paper red

On the other hand, bases:

  • Taste bitter (like caffeine in coffee)
  • Feel slippery
  • Turn red litmus paper blue

Note:  Scientists know:  never taste, drink or eat anything from a science experiment!

Chemists have created a scale to measure how acidic or basic a substance is, called the pH scale. Although no one knows for sure how the name pH came to be, it is acceptable to think of pH as the “power” of hydronium ions, or "how many hydronium ions are present." (Hydrodium ions are technically H3O+ ions, but are often written as H +.) It is a logarithmic scale, which means that lower numbers, like 1 or 2, indicate a larger number of hydronium ions, and that a substance is more acidic.

Gather at least some of the following possible acids or bases to test:

  • Lemon and/or orange juice
  • Apple juice
  • Soda (pop)
  • Vinegar
  • Baking soda (mix with water to moisten)
  • Dish and/or laundry determent
  • Shampoo
  • Milk of Magnesia
  • Coffee
  • Salt
  • Cream of Tartar (in water to moisten)

Add any other household materials you might be curious about, but only under adult supervision.

Note: Bleach doesn't work well because it interferes with the dye molecules. Also, adding vinegar to baking soda is fine, but do not mix strong acids and bases.

Gather small clear containers such a plastic cups or clean baby food jars to carry out the experiments in. Label each container when you add a substance to be tested so you remember which is which.

Plant-Based pH Indicators

Certain molecules and substances change color when exposed to specific acidic or basic conditions, and thus can be used as pH indicators. Examples of  pH indicators from plants include: 


1. Litmus is a complex of dyes extracted from certain lichens. 

Litmus paper is a classic for exploring acids and bases. All you need to do is dip the litmus paper strip into the liquid to be tested. If the blue litmus paper turns red, it is an acid. If the red (pink) litmus paper turns blue, it is a base. If neither changes, the substance you are testing is neutral.

Litmus paper is available online or in science supply stores. Pool supply and aquarium supply stores may also carry it.

2. Anthocyanins- derived from red or purple fruits and berries, such as:  red cabbage!

red cabbage indicator

I know, I know, red cabbage indicator is all over the Internet and has been probably over-exposed, but that is because it is easy and works for both acids and bases. If you haven’t done this, it really is fun. Even if you have done it before, pull it out again and try something new with it. Using red cabbage as a pH indicator works well for an activity with mixed-age groups because each age may achieve a different level of understanding. If you are really tired of red cabbage, try the juicing beets (the root part), or berries instead.

All you need is red cabbage from the grocery store and a blender.

Some recipes call for boiling the cabbage but that is smelly and unnecessary. Simply grind up the fresh red cabbage leaves in small batches with just enough water to allow the blender to work properly. Pour the batches together in a pitcher (which can be placed in the refrigerator for use later in the day if necessary.) You can also strain the slurry through a strainer to remove the solids.

Pour about 1/3 cup of the red cabbage juice into testing containers such as clear glasses or plastic cups. Mix in about a Tablespoon of one of the testing compounds into one of the containers and label it. Does the color of the liquid change? Have fun admiring the wild colors you can make.

Try another material in the next container.

Questions to try:

  • Does the color change more if you add more test material?
  • Can you figure out which colors indicate acids and which indicate bases?
  • Does the temperature of the liquid matter? Hot or cold?
  • How does the color change when you add baking soda to vinegar with the cabbage juice already in it? Can you add enough vinegar to turn the color back? How much does it take?
  • What happens when you dilute the test mixture with water?

What is happening? The pigment molecules in the red cabbage juice change shape, and thus color, when in the presence of acids or bases. Lemon juice, vinegar and soda are acids; detergents and soaps are bases. In the above photograph, from left to right are:  red cabbage juice in water, dish detergent, baking soda in water and lemon juice.

Edit:  Sarah of Share It! Science blog just stopped by with a link to a post about using the anthocyanins in poinsettia bracts (the red ones) as a pH indicator.

3. The third pH indicator is curcumin, which is found in turmeric.


  • Paper towel
  • Isopropyl (rubbing) alcohol
  • Paper plate or waxed paper
  • Turmeric (sold in the spice aisle of most groceries)

Watch out, turmeric will stain like crazy! Wear old clothes and do this outdoors, if possible.

Cut paper toweling into strips. Mix a few teaspoons turmeric with isopropyl or rubbing alcohol in a small container. Dip the thin strips of paper towel into the solution. Pull out and allow the paper towel strips to dry on a disposable or stain-resistant surface, such as a paper plate or sheet of wax paper. The alcohol should evaporate fairly quickly.


One the strip are dry, dip them into test substances placed in small containers, as discussed above.


 Note: Turmeric is bright golden yellow below pH 7.4, orange above pH 7.4 and bright red above pH 8.6.

Extra turmeric strips can be stored in a plastic bag for later use (up to months).


Check our Chemistry Week Table of Contents for more children's chemistry activities.



What are elements, atoms and molecules? How do we study them?

Chemistry Vocabulary:

Elements- Chemists have identified substances that can not be broken down further using chemical means. These are called the elements. Examples of elements are oxygen, carbon and gold. Jefferson Lab has a list of the 10 Most abundant elements in the universe.

Atoms- Atoms are the smallest units of elements. They are also what makes up all the matter in the universe.

Molecules- Many elements are found in nature as two or more atoms interacting together. When two or more atoms interact together or bond, then the result is called a molecule.

Atoms from different elements can also form molecules. An example of a molecule of this type is water, which is formed of hydrogen and oxygen atoms.

A friend used to ask me, “Has anyone ever seen an atom?” Recently scientists have developed technology that allows us to do just that. It is called an atomic force microscope/scanning tunneling microscope. They use extremely cold conditions to hold the atoms or molecules still enough to visualize. Want to see what they look like?

A Boy And His Atom: The World's Smallest Movie

This is a stop motion animated movie created using images from a scanning tunneling microscope. Note: This should really be called a boy and his molecule, because the researchers moved carbon monoxide (CO) molecules to create the images.

Moving Atoms: Making The World's Smallest Movie

In the video below you can see how researchers made A Boy and His Atom. You can also see how excited the researchers are to be doing this creative project and how it has practical applications. It is well worth watching.


Related activity:

Make An Element Collection

One great way to make chemistry more concrete is to have have experience with the pure form of different elements.


  • A periodic table of the elements ( has some to download for free)
  • Box for holding the collection
  • Paper and pen or computer for generating labels
  • Tape or glue (for attaching labels)
  • Small vials for holding samples (optional)
  • Elements

Caution:  Some elements are gases at room temperature, and would be hard to hold in a collection. Some elements, such as mercury, beryllium, and arsenic, are toxic and should not be collected by children.

Elements that you can find at home, hardware supply stores, department stores, rock shops, etc.

  • Carbon:  coal, charcoal
  • Copper:  plumbing supplies
  • Aluminum:  foil, pots and pans
  • Iron:  nails, some magnets
  • Magnesium:  Campfire starters (warning:  highly flammable!)
  • Tin:  new lead-free fishing sinkers
  • Lead:  older fishing sinkers (handle with rubber gloves and wash hands afterwards)
  • Silicon:  computer chips
  • Platinum, gold, silver:  jewelry, small amounts available at bead stores
  • Lithium:  specialized batteries
  • Sulfur:  rock and mineral shops
  • Zinc:  Galvanized nails, electrodes in lemon battery kits (can be toxic if sufficient amounts are swallowed)
  • Tungsten:  Light bulb filaments
  • Neodymium:  Magnets (very powerful, handle with care)
  • Nickel:  Many neodymium magnets are nickel-plated
  • Titanium:  bicycle parts

Always label the items in your collection with the name of the element, and when and where you collected it. That way you won't forget what it is and you can tell your friends where you found it.

You might also want to include elements in common compounds (not in pure form):

  • Sodium:  Table salt (Sodium Chloride)
  • Iodine:  Iodized table salt
  • Calcium:  Chalk, antacids (Calcium carbonate)
  • Magnesium:  Epsom salts (Magnesium sulfate)

Collecting elements can tie in nicely with a rock and mineral collection. For example, look for rocks with copper, sulfur or iron. Panning for gold is fun, too.

copper-mineralsCopper is found in many minerals including azurite and malachite.

Looking for more information? Try:

The Elements: A Visual Exploration of Every Known Atom in the Universe by Theodore Gray, with photographs by Nick Mann

To get an idea what the book is like, Theodore Gray has his periodic table of element photographs at To look at each element, click on the photograph.

Paperback: 240 pages
Publisher: Black Dog & Leventhal Publishers; Reprint edition (April 3, 2012)
Language: English
ISBN-10: 1579128955
ISBN-13: 978-1579128951


Slide1Check our Chemistry Week Table of  Contents page for links to all our activities.