Introduction: Kitchen Chemistry
Experiment with small quantities of ingredients from your kitchen cabinets to explore basic chemistry: what does it mean when something mixes, dissolves, or reacts? Some of the combinations may be predictable, some surprising. What ingredients are responsible for the different results? Everyone will have different ingredients and this will make it interesting to share our results.
This workshop was designed for out-of-school-time educators as a family workshop (children with an adult present) but can be easily adapted to other educational settings. The activities are suited to remote learning since they use common materials, and not every participant needs to have the same ingredients. In fact, everyone having different ingredients will make it interesting to share results.
Facilitator Notes: The workshop helps ground some fundamental chemistry concepts in a very approachable way: by experimenting with familiar food ingredients. Participants will observe the ingredients closely, and the facilitator can help link participants' observations to chemistry concepts. Concepts include liquid and solid, and different properties of solids including crystals, grain sizes, etc. (See the glossary for basic explanations of chemistry terms.) Experimenting with mixing different ingredients brings in the ideas of mixtures, suspensions, solutions, emulsions, dissolving, density, chemical reactions, pH, and more. Don’t overwhelm the conversation with the technical terms — it is better to focus on the experiences with real materials, observations, and investigations. Introduce the chemistry vocabulary when it will help give a name to what participants are observing, or it will help explain what is happening on an invisible (molecular) level.
The outline is written assuming participants have little background chemistry knowledge. Fundamentally the activity is about observation and encouraging participants to learn by working with the materials. As a facilitator you do not have to know all the chemistry involved — indeed food chemistry gets complex quickly, and few people could claim to understand all the chemistry involved. However, knowing some of the basic ideas can help you point out interesting phenomena, link observations to chemistry topics, and suggest potential further avenues for investigation.
Be Safe: Use food ingredients only! (No cleaners or things from under the sink!) This activity assumes the adult member of each participant group is responsible for safety and modifying the activities to address any possible food allergy issues.
We will use small quantities of each ingredient (a few tablespoons at most). Don’t use anything too expensive -- like vanilla or spices.
Have participants gather supplies from their kitchen — one thing from your kitchen cabinet or refrigerator for each category below. At this point, participants should keep the ingredient in its bag, box, or bottle:
- One Liquid ingredient (for example, juice, vinegar, oil, etc.)
- One dry ingredient (for example, salt, sugar, flour, baking soda, etc.)
- A blue or purple vegetable or fruit (if they have one)
- Two or more small zip lock bags (if available), otherwise any clear containers (glasses, small jars, clear plastic containers, clean baby food jars, clear plastic egg carton from recycling, or other)
- Measuring spoons: ¼ teaspoon, 1 tablespoon (if not available substitute any small spoons)
- A couple of small spoons, stir sticks, or something to stir with
- A magnifying glass (if available)
- Dishcloth or paper towel
Step 1: Gather the Ingredients
Have people gather their ingredients if this has not been done in advance.
Step 2: Investigate Your Dry Ingredient
As participants finish collecting their materials, have people start the first investigation:
Have each participant put 1/4 teaspoon of their dry ingredient into a zip bag (or other container) and investigate it.
Some questions are below, and you can use them on screen to help prompt the investigation.
Investigate your kitchen chemistry ingredient: Put ¼ teaspoon of your dry ingredient in a container.
- Look at it — how would you describe it? (Color, texture, shape?)
- Look as closely as you can (use a magnifying glass if you have one). What do you see?
- Rub a pinch between your fingers. What does it feel like?
- Does it have a smell?
- Does it make a sound if you shake it?
Step 3: Investigate Your Liquid Ingredient
Talk about exploring, observing, and being surprised by common food ingredients.
Then have participants take a second container and put in one tablespoon of their liquid ingredient. (1 tablespoon = 3 teaspoons)
Investigate the liquid ingredient using the same questions as above.
Step 4: Combining
The next step is to try combing your two ingredients.
Pour the 1/4 teaspoon of the dry ingredient from its bag (or other container) into the liquid bag. Don’t stir them yet. Just observe what happens when you pour them together. Have people share, and show, what they observe.
- Did they mix?
- Not mix?
- Float or sink?
- Other observations?
- What things happened that you expected?
- What was surprising?
- Were there any reactions (see the glossary for a definition)?
Step 5: Mixing
Now have participants stir their ingredients together, mixing well.
- What happens when you stir? Talk about dissolving, not dissolving, mixing or not mixing, and other observations.
- Were there any surprises?
Try using the same dry ingredient (1/4 teaspoon) but this time mixing it with 1 tablespoon of water in a new bag or container.
- What happens?
- Did it act differently from your original mixture?
Step 6: Taking It Further: More Mixtures
If you have time:
- Encourage participants to try a second dry/wet mixture using a new container.
- Try mixing two liquid ingredients.
- You can try some interesting three-way combinations. For example, oil and vinegar will separate quickly when mixed. If you add an emulsifier such as mustard or mayonnaise, the mixture will not separate as quickly. This is a good trick when you are making salad dressing!
- There are some cool things you can make from common ingredients (see play-doh and oobleck in the References section). These can be good follow-up activities.
Step 7: Taking It Further: Reactions
Some of the mixtures you tried may have resulted in chemical reactions (see glossary). Reactions are often surprising since the result can be very different from either starting ingredient. If no one happened upon a reaction, you can have participants find two reactive ingredients -- for example, baking soda and vinegar. (See the background information for other reactive possibilities.)
When baking soda and vinegar are mixed they bubble and release carbon dioxide gas (use the same ¼ teaspoon dry to 1 tablespoon wet ratio). If not all students have these ingredients, one student can demonstrate the reaction for others.
Step 8: Taking It Further: PH
If no one tried a pH reactive substance, see if someone has one of these ingredients, or you can demonstrate it on screen. These are fun reactions to observe since they change color!
A number of blue and purple fruits and vegetables contain substances (anthocyanins) that change color when you change the pH by adding acidic or basic ingredients. Common pH indicators include purple cabbage and blueberries. You need to mash or boil them in some water to release the colored chemicals into the water.
Adding an acidic or basic ingredient to the mix will then change the pH and probably the color. Try adding 1/4 teaspoon of baking soda (a base), or lemon juice (an acid).
How many different colors can you make?
You can alternate adding a base and then an acid -- changing the color back and forth, and back again. It works best if you add very small amounts at a time.
Step 9: Wrap-up
Cooking uses many chemical principles, some that we observed, and lots more! Chemistry is not just a school subject, it is a way scientists help to explain why things happen in the world when we mix, heat, react and use different materials. Chemistry is the science of chemicals, but what is a chemical? Some of the ingredients we experimented with are made of one thing — like salt. It is a chemical. Some ingredients are mixtures of many chemicals — for example, flour (and many other things in our kitchen cabinets) are made of ground-up plants or parts of plants — and plants are made up of lots of different chemicals. Some things, like vinegar or juice, are a mixture of water and other chemicals. In fact, everything in the whole world is made of one or more chemicals. Chemistry is the science of chemicals — the solids, liquids, and gasses around us — and of the reactions between chemicals involved in cooking food, making new materials, and keeping our own bodies healthy and growing.
Step 10: Background Information
Let participants enjoy the surprise of what happens when different ingredients are mixed. However, as the facilitator, it is helpful to familiarize yourself with some of the possible interactions that participants are likely to observe. This way you can help point out interesting features if participants miss them, or help them explain what they have observed. Using the information below you can also suggest some interesting combinations if no one happens upon them.
What follows is an incomplete list of some of the results that you are likely to encounter in the workshop. Ideally, you will also find some surprises!
- Salt (sodium chloride): a mineral that is mined, or collected from evaporated seawater. Sodium chloride is table salt, but there are other salts that have elements other than sodium (for example Epsom salts, magnesium sulfate, or calcium chloride used for melting snow). Salt is sold in crystals of various sizes, which you can see under a magnifying glass. Salt dissolves in water, or in other liquids such as vinegar that are mostly water. It is not soluble in oil. By adding a little salt at a time you can see how much salt will dissolve in water.
- Sugar (organic molecule): sold as small crystals (you can see the shape under the magnifying glass) or as powdered (ground) sugar. Sugar is made from plants, but unlike flour, it is a single compound, not a ground-up part of a plant. Like salt, it will dissolve in water, and is not soluble in oil.
- Flour (ground plant): most often made from the seeds of wheat, but other grains can be used (oat flour, rice flour, etc.). As a plant product, flour contains many different chemicals including starches and proteins. It will absorb water.
- Baking Soda (Sodium bicarbonate): reacts with any acid (including vinegar, lemon juice, etc). The reaction produces bubbles of the non-toxic gas carbon dioxide, as well as a type of salt residue. Small amounts of baking soda will dissolve in water, but the water gets saturated quickly and no more will dissolve.
- Baking Powder (mixture): baking powder includes baking soda as well as other chemicals (check the ingredients). These produce carbon dioxide gas when you add an acid or water.
- Potato starch or cornstarch (organic compound): starches absorb a lot of water and so they are used in thickening soups and sauces.
- Vinegar (acetic acid and water): the acetic acid gives vinegar its key smell and taste. Some vinegars also contain sugar, or various plant chemicals that add flavors.
- Oil (organic compound): Oil includes the basic oil (the exact chemical composition depends on the type of oil) as well as other plant compounds that add unique flavors. Salt or sugar are not soluble in oil, they will just sink to the bottom of the oil. Oil is lighter than water and will float to the surface. “Emulsifiers” can help keep oil and water-based substances mixed for a longer period of time, for example when you make salad dressing with oil and vinegar and add mustard (see resources).
- pH Reactions: pH refers to whether something is an acid (like vinegar or lemon juice) or base (baking soda, for example). A number of blue and purple fruits and vegetables contain substances (anthocyanins) that change color depending on the pH. These are fun reactions to observe. Common pH indicators include purple cabbage and blueberries. You need to mash or boil them in some water to get the juice. Then try changing the pH by adding an acid or base.
Step 11: Glossary
There are many specialized terms used in chemistry. Some are confusing since they have a common usage, as well as a scientific meaning when used by chemists. For example, sometimes when people say something is a “chemical” they mean something dangerous. To a chemist, the whole world is made up of chemicals, some toxic, some that make up our food, buildings, and objects. Here are a few terms that can help in this workshop:
- Atom: Atoms are building blocks, the smallest unit you can have of an element. For example, you can have one aluminum atom. If you break that up, you no longer have aluminum, only a bunch of subatomic particles: electrons, protons, and neutrons.
- Element: a single type of atom. Some materials are a single element, for example, aluminum is an element. There are 118 elements that make up our world, some exceedingly rare, others extremely common. But these basic elements can combine with each other, making a nearly endless number of other compounds.
- Molecule: a group of atoms joined together. In some cases two or more of the same type of atom can join, for example, the oxygen in the air is O2, a molecule made up of two oxygen atoms. Often, two or more elements join together. For example, a water molecule contains two hydrogen atoms and one oxygen atom joined together.
- Chemical or Compound: a substance made up of one type of molecule.
- Organic Chemistry: Plants and animals produce some very complex chemicals which are built around the elements carbon and hydrogen (greetings fellow carbon-based life form!). These include sugars, starches, fats, and proteins. These molecules may consist of hundreds or thousands of atoms and have complex three-dimensional shapes. Organic chemistry studies the sorts of chemicals produced by plants and animals and the reactions between them. This is what makes food chemistry complex -- and interesting!
- Crystal: when many molecules of the same type link together in a geometrical pattern. Water crystallizes when it freezes, salt forms crystals. Different crystals have distinctive three-dimensional shapes.
- Powder: something ground up. Sugar, for example, can be sold in crystals, or as powdered sugar where the crystals are ground up. Many kitchen ingredients are made from ground parts of plants.
- Mixture: when you mix two chemicals. Sometimes two mixed substances don’t interact. For example, if you mix sugar and salt crystals you get, well, a mixture of sugar and salt crystals. But different things can happen when chemicals are mixed, as described below.
- Suspension: when particles of one substance do not dissolve but stay suspended in a liquid. For example, orange juice is a suspension with pulp suspended in the liquid juice.
- Dissolve: some substances dissolve (are soluble) in other substances, some are not soluble. For example, salt dissolves in water. The molecules of salt leave their crystals and spread out throughout the water. When the salt is dissolved you can no longer see it (salt is colorless), but the salt is still there. You can taste it. If you let the water dry out, you will see the salt crystallize again. Many common kitchen ingredients will dissolve in water, some in oil.
- Absorb: flour or other plant-based ingredients may absorb water; the water sticks to substances in the flour.
- Chemical Reaction: sometimes two chemicals will react with each other -- one or both of the types of molecules split apart and recombine in new ways. All the same types of atoms are still there, but they are combined into a new substance or substances. Reactions can be surprising because the result may look nothing like the original ingredients. For example, if you mix baking soda (a powder) and vinegar (a liquid) together, one result is carbon dioxide: a clear non-toxic gas.
- Viscosity: The “thickness” of a liquid -- how quickly it flows or moves when you pour or push it around. For example, honey is more viscous than water.
Step 12: Reseorces
(Search Instructables for other recipes)
This work is made possible by support from STAR, a Biogen Foundation Initiative. The team at Lesley supporting this initiative includes faculty and staff in the Lesley STEAM Learning Lab, Science in Education, the Center for Mathematics Achievement, and other related Lesley University departments and programs.
This is an entry in the
Explore Science Challenge