Chemistry for Kids: Hands-on Activities for Learning About the Chemical and Physical changes

Young chemists love to make things happen and what better way than through physical changes and chemical reactions! Let’s get started!

What is a Physical Change

A physical change is any change to a substance that does not alter its chemical composition. An example of a physical change is a state change - when matter changes from a solid to liquid, or liquid to gas, or vice versa. This is a physical change because the substance stays the same, it is just in a different form. In other words, ice, water, and steam are all H2O, just in different forms. 

Another kind of physical change is a mixture. A mixture is when you combine two or more substances that do not react with each other chemically - they do not change their chemical structure. The substances combined each retain their own identity. Salt water is one example where it is easy to see that two substances are mixed together but do not change their identities.

Try mixing 1/2 tsp of salt in a cup full of water, and 1/2 tsp of sugar in another cup of water. What happens to the sugar and salt? Can you still see it? Is it still there? Try tasting the solutions. Can you tell that the sugar and salt are still there? Is there any way to get the sugar or salt out of the water again? How? Try boiling the the salt water in a pot until the water is all gone. What happened? The salt is still there! That is because in the solution, the water remained water and the salt remained salt, they were simply mixed together. That is a physical change.

What is a Chemical Reaction?

A chemical reaction, also called a chemical change, is when matter changes chemically and a new substance is formed.  The atoms or molecules in the matter are rearranging to create something different from what was originally present. Usually this change is not reversible and usually there is evidence of a chemical change in the form of heat, light, fire, bubbling, odor, a color change, formation of a gas, or formation of a solid. Let’s take a closer look.

Heat, Fire, Light, Odor

Light a candle. What do you observe? What kind of a change is taking place? If you guessed a chemical or physical change, you are right! Both changes are taking place. The wax on the candle is melting, which is a physical change. There is also fire, light, heat, and an odor, which are clues that a chemical change is taking place.

Formation of a Gas

This is a simple experiment, but it is a really fun one too!

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You will need:

  • about 1 tsp. of baking soda

  • a funnel

  • an empty water or soda bottle, rinsed out

  • about 1/4 cup of vinegar

  • 1 eight inch balloon

Put the funnel in the end of the balloon and carefully pour the baking soda in. Pour the vinegar into the bottle. Take the balloon and pick the end so the baking soda stays in the bottom of the balloon. Carefully stretch the balloon over the opening of the bottle, being careful not to let the baking soda fall in. Now, hold the balloon up and let the baking soda fall in. Watch what happens! The balloon quickly inflates. Why? The vinegar and baking soda created a chemical reaction! The chemical reaction produced carbon dioxide gas which inflated the balloon. So we see how a chemical reaction can form a gas.

Change in Color

For the next activity you will need:

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  • cornstarch

  • providing iodine (you can find this at any drugstore)

  • an eye dropper or pipette

  • a vitamin C tablet, crushed and mixed in 1/4 cup of water

Scoop a small amount of cornstarch onto a paper plate. Mix a few drops of iodine in a cup of water. Now, use your pipette or eye dropper to drop a drop or two of your iodine solution onto the cornstarch. What happens? It turns dark purple or blue! How does that happen? It is a chemical reaction between the iodine and starch molecules.

Now, scoop a little of the starch into your cup of iodine solution. Did it turn a dark color? If not, add some more starch. When your solution is dark, drop a few drops of your vitamin C solution into the cup. What happened? It turned light again! This is another chemical reaction. The vitamin C, or ascorbic acid, reduces the iodine to iodide so the starch returns to its normal color.

Formation of a Solid

Make Rubber Ball

You will need:

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  • 1/2 tsp borax

  • 1 tbsp glue

  • 1 tbsp cornstarch

  • water

  • a paper or plastic cup

-Mix 2 Tbsp warm water and 1/2 tsp borax in a cup, stir until dissolved

-In another cup mix 1 Tbsp glue + 1/2 tsp borax solution. Add 1 tbsp cornstarch and let sit for 15 seconds

-Stir until fully mixed, then when you can no longer stir it, take it out and form a bouncy ball. Try bouncing it on the floor. You have formed a solid through a chemical reaction between glue and borax! Keep your new bouncy ball in a plastic bag until you are ready to play with it again.


Which one was a chemical change? 

In some reactions, it can be hard to tell if a physical change or a chemical change has taken place because they can look a lot alike. In this activity, we will compare two similar reactions and see if we can figure out which one is a chemical change.

Reaction #1 Soda and Mentos

You will need:

  • 2 liter diet soda of any kind

  • 1 roll of Mentos mint flavor

  • hot glue gun and glue

Instructions:

Open the roll of mentos and glue each individual mint together with hot glue into one tall tower. Set the soda and Mentos tower aside while you prepare the second reaction.

Reaction #2 Elephant Toothpaste

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You will need:

  • 1/2 cup of hydrogen peroxide

  • one squirt of dishsoap

  • one packet of yeast

  • warm water

  • one empty 16 oz. soda bottle or water bottle

Instructions:

Pour 1/2 c. hydrogen peroxide into the empty bottle. Add a squirt or two of dish soap and swirl the bottle to mix it into the hydrogen peroxide. In a cup, mix 1/4 cup of very warm water and the package of yeast.

Now that both reactions are prepared, take your bottles, Mentos, and cup of yeast outside or to another place that’s easy to clean - this will make a mess! Now, put your Mentos tower in the soda bottle and watch what happens. When it stops bubbling, pour your cup of yeast into the bottle of hydrogen peroxide and dish soap. What happens? Check both reactions for signs of a chemical reaction. What did you observe? Make sure to get a good look at, smell, touch each substance that comes out of the bottles.

While both reactions bubble and almost explode in a similar way, only the elephant toothpaste is a chemical reaction. How can you tell? It created heat! While the soda and Mentos appeared to create a gas, the Mentos were really only helping the carbon dioxide already in the soda to escape, much like when you shake a can of soda and then open it.

Chemistry for Kids: Hands-on Activities for Learning About the pH Scale

In chemistry, we often talk about the pH of various substances, but what exactly does that mean? Let’s find out!

What is the pH Scale?

pH stands for potential for hydrogen. Look at hydrogen on the periodic table. How many protons does it have? How many electrons? Look at a diagram of hydrogen. What do you remember about what atoms like to do with their orbitals? They like to fill the outer ones (called valence shells) up or empty them. Since hydrogen only has one electron, it is a pretty reactive atom! It likes to give an electron or get one, and thereby bond with many different atoms. Potential for hydrogen, or pH, refers to what is happening to hydrogen in a compound.

The pH scale is a scale from 0-14. 7 on the pH scale is neutral. Water has a pH of 7. Anything lower than 7 is acidic - the acidity gets higher as the number gets lower. Anything greater than 7 is a base or alkaline and its alkalinity gets higher as the numbers get higher. 

Acids like to give away hydrogen ions. They are sour and they react with metals, so they are corrosive. Acids can also be damaging to living tissue. Bases like to collect hydrogen ions. They are bitter and slippery. They are good at dissolving fats. Because of this, most soaps are basic. A strong base can also be damaging to living tissue.

Let’s do an activity to become familiar with the pH of everyday substances.

Mystery Liquids

For this activity you will need:

  • 8-10 small cups for each child who will do the activity

  • litmus paper

  • 8-10 different liquids ranging in acidity and alkalinity

  • a sheet of paper to keep track of your results

Number 8-10 small plastic cups. Gather an assortment of acidic and basic liquids. Some liquids you might use are: tomato juice, soda, orange juice, baking soda water, lemon juice, vinegar, milk of magnesia, dish soap (thin it slightly with water), hand soap (thin it slightly with water), and glass cleaner. Make sure to include water in your assortment. Fill each cup halfway with one of the liquids. Be sure to keep a numbered list so that you know what liquid is in which cup.

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Have the children test the pH of each liquid with the end of a litmus strip. Compare the color on the strip to the pH scale that comes with your litmus strips. Which of the liquids is the most acidic? Which is the most basic? Can you guess what each of the liquids is? Have the children record their results!

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Chemistry for Kids: Hands-on Activities for Learning About Compounds, Polymers, and Crystals

Today we are going to learn about compounds! When different atoms join together they form a compound. Compounds can range from a simple molecule to more complex structures, such as polymers and crystals.

Let’s investigate what some simple compounds look like.

Molecule Match

In this activity, we will build molecules and match them to their chemical formula and name in order to help us become familiar with some different molecular shapes and molecular formulas.

Use a molecule building kit such as Molymod or the Molecular Student Set . Snatoms would also work well and they look really fun, but they are more pricey. Print some pictures of molecules online or draw your own.

On small pieces of paper or notecards, write the names of the molecules and their chemical formulas. Make a key card with the name of each atom, its symbol, and model color.

Now put the pictures of molecules in one stack and lay the name/formula cards out so they can all be seen at once. Have the children build each molecule with the building kit, then match the molecule with its name and formula.

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Now let’s talk about some different ways molecules and atoms can combine to form more complex structures.

Polymers

Give the children a simple crocheted chain or yarn, or something similar (you can find easy instructions for hand-crocheting a chain online). The children can make the chains themselves, or you can pre-make them. Direct the children to notice how even though the yarn itself is not stretchy, the chain can stretch, twist, and bend, and then return to its normal shape.

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Polymers are like this. A polymer is a compound in which the molecules are arranged in a repeating pattern that is like a chain. Because of this, polymers are resilient, they tend to be flexible, and they are sometimes stretchy and pliable. Can you guess what things around you might be polymers? Rubber, wool, cotton, silk, and spider silk are examples of polymers. Cellulose, which is found in plants and in wood, is a polymer. Can you guess what things on your body are polymers? Your hair, nails, muscles, organs, and skin contain polymers, and your DNA is a polymer! That’s right - the chains that make up your DNA and RNA are actually polymers! Polymers are found abundantly in nature, and they are also manmade, such as plastic and manmade fabric such as polyester and rayon.

Let’s make a polymer!

This is what you need:

  • 4 oz of school glue (this is a regular sized bottle of glue)

  • 3/4 c. warm water

  • 1 tsp borax mixed into 1/4 c. of water

  • food coloring (optional)

In a small bowl, mix the glue and 3/4 c. water. Add the food coloring, and then add your borax solution a little at a time until your polymer begins to take shape. Once it begins to take shape, take it out and knead it together until you have a stretchy, slimy goo! This recipe will give you a pretty viscous polymer that is a little bit stretchy. You can reduce the amount of borax to make a more slimy goo that is more stretchy.

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Play with your polymer and observe its qualities. What can you make it do?

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Crystals

Crystals have a different molecular arrangement. A crystal is a solid that is formed when atoms or molecules are arranged in a repeating pattern that is three- dimensional. Some elements that form crystals are: carbon, silicon, aluminum, magnesium, iron, and calcium. Some compounds that form crystals are salt, sugar, and water. 

Take a look at some sugar and salt crystals through a microscope. What do they look like? Draw a picture!

We used an  Amscope  to look at salt and sugar crystals.

We used an Amscope to look at salt and sugar crystals.

Let’s make a model of a salt crystal!

NaCl, which is sodium chloride, or table salt, is a cubic crystal that alternates atoms of sodium (Na) and chloride (Cl). Take toothpicks and two colors of marshmallows and build one!

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Notice that in our NaCl model, we made sure to alternate two colors - one to stand for sodium, and one to stand for chloride. A marshmallow is not adjacent to the same color marshmallow in any direction, because in sodium chloride, a sodium atom is not adjacent to another sodium atom, and the same is true for chloride. They alternate because they have ionic bonds.

Hot Ice

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This is a super fun activity in which you can watch crystals appear before your eyes! This is how it works: create a super-saturated solution of sodium acetate by dissolving a lot of sodium acetate in a small amount of water by heating it up. Allow the solution to cool, then add a single crystal of sodium acetate and watch the crystals form like magic! This works because the solution is super saturated, so it is very unstable. The crystals are eager to come out of the solution, so when given a nucleation site (a crystal to build on) they immediately form on top of it.

Here are the instructions for forming the solution:

Hot Ice Instructions

  • scoop 160 grams of sodium acetate into a glass jar or container (I used this kind) (if you don’t have a scale that measures grams, this is slightly less than 1 cup - I would say a scant 1 cup)

  • pour 30 mL of water into the jar

  • Microwave in increments until the sodium acetate is completely dissolved and you see no more particles (start with 2 minutes and add 1 minute or 30 seconds at a time after that, depending on how much solid matter is still in the solution).

  • When all of the sodium acetate is dissolved, cover the jar and let the solution cool to room temperature. Do NOT pour the solution out of the jar until you are ready to use it. Try not to disturb the jar either - you might begin the crystallization process before you are ready. Should your solution crystalize before you are ready to use it, just add a tiny bit of water (about 1/4 tsp) and heat it up again until it is completely melted.

  • Once your solution has cooled, you can do one of several things:

    You can place a crystal of sodium acetate on a plate and slowly pour your solution on top of it. Watch a crystal tower form before your eyes! Be sure to notice the heat that it gives off as it crystalizes. This is called an exothermic process, because the formation of the crystals gives off heat.

You can also drop a crystal into your jar and watch as crystals fan out from the nucleation site until all of the solution is crystalized. You can also start this process with a spoon or even by shaking the jar a little.

You can reuse your sodium acetate solution over and over! Just melt it down again in a clean jar. Microwave it in increments until it is completely liquid. Start with 1 minute and go from there. You might need to add a tiny bit of water - 1/4 to 1/2 tsp. before you microwave it. But don’t add too much or your solution will not be saturated enough to form your crystals.

Note: you can find instructions for creating the sodium acetate solution using baking soda and vinegar, but I do not recommend trying to do it that way. It is difficult to get it right and it will make your house smell terrible and your eyes burn because you have to boil it for so long (speaking from experience!).

Also - you can divide this recipe in half or in thirds and it still works just as well. The amount that the recipe makes will give you a good sized crystal tower. I recommend dividing the water and sodium acetate into a few jars (do this before you heat it) so you can try forming the crystals in a few different ways.

Have fun and let me know how it works!