Kitchen Science: Acids, Bases and Common Kitchen Chemical Reactions
Chemistry doesn’t have to wait until high school. You and your child can create impressive chemical reactions in your kitchen now, right before his eyes. Lessons in chemistry can be as simple as combining ingredients used everyday in cooking. With some help, your child will discover materials that when combined produce results representing foundational ideas of chemistry; concepts that are easy to grasp when seen and result from your child’s own actions.
Today, let’s talk about acids. Acids are used in meal preparation regularly and often, perhaps even daily. So as you pull out the vinegar to prepare a salad dressing, or squeeze lemon juice onto a filet of fish, and your child is “helping” and interested, start asking questions and initiate discovery.
This discovery can take place across many days and the preparation of many different meals. It is a time when you are in the kitchen having to prepare a meal anyways, so take advantage of these opportunities and combine a little science with making dinner. The more often something is discussed and investigated, the deeper the learning. Remember it is best to initiate these discussions when your child asks a question or seems to be puzzling over something. Yet, a comment from you, “I wonder…,” can jumpstart these discussions.
There are many common science experiments for kids that share a focus on basic principles in chemistry. Chemistry is the study of substances and how they interact with other substances. The following steps of inquiry focus on acids and bases, their interactions and the chemical changes that result. Acids are a good place to start because they are common in foods, and every kid is familiar with how the mouth puckers in reaction to tasting an acid.
Below you will find a compendium of those experiments, and many of them will produce interesting and exciting visual effects. So pick and choose or try them all, but remember your goal is to instill an appreciation of:
• a (chemical) change can take place when substances interact or are combined,
• some fundamental differences between an acid and a base,
• differences between states of matter, or solids, liquids, and gasses.
Remember the facts of science are less important than engagement in hands-on activities at this point. So, you will be asking questions that are intended to help your child experience these principles of chemistry but don’t necessarily expect to hear that information verbalized back. Just let it sink in. More important is strategizing on how to ask a different question or design a different experiment.
In general, the more sour something tastes, the more acidic. We will be examining acids in the kitchen that are okay to taste, or touch. Acids are important in cooking adding flavor and helping to preserve food. However, many acids are too dangerous to handle, much less put in your mouth. Although this piece of information may have to wait until your child is older, for your information, most acids are made of one or more hydrogen atoms.
Bases, when dissolved in water, are slippery to the touch and taste bitter. The base you will work with the most is baking soda, which is used to help cakes rise. Bases are also referred to as alkaline or alkali.
Both bases and acids can conduct electricity, but we’ll save those experiments for another time.
Neutral substances are neither an acid nor a base.
Look, feel, taste, smell and describe the variety of ingredients listed throughout these suggestions. During some of the experiments included below, you may even be able to list sounds that could be helpful in distinguishing what is happening (bubbling, fizzing). (Adults will have to make determinations about the safety of handling or tasting substances).
Observe the surface of those liquids in a tube or glass so that your child can see whether or not they cling to the edge of the container. Observe surface tension, does it appear as though you are pricking through the surface?
How do the acids in your kitchen smell? Do lemon juice and vinegar smell the same? Do vinegar and baking soda, which is a base, smell the same?
Taste a variety of acids (lemon juice, lime juice, pineapple juice, various vinegars, juice from a pickle jar). Do they taste the same? How are the similar or different?
Compare and Contrast
Having made a variety of observations, classify these substances in your kitchen cabinets into groups representing the three categories chemists use (acids, bases, neutral). Or suggest categories based on fluids (liquids) versus solids. Or, allow your child to employ her own classification scheme, just make sure you encourage her to articulate her strategy (I see you are putting these into groups. Can you tell me how you are deciding which group they go into?).
Either cut up or find pictures of several orange foods, including oranges, tangerines, cantaloupe, carrots, butternut squash, yams, orange tomatoes, apricots, orange peppers, certain crackers, and cheeses. Next sort or arrange by the level of acidity as determined by taste. In general, the more sour it tastes, the more acidic it is.
Examine lists of ingredients on food labels of items in your pantry. Encourage your child to classify these. Options include the number of acids in the label, the types of acids, or acids or no acids.
An easy and safe measurement tool for working with acids and bases is litmus paper. Bases will turn red litmus paper blue while an acid will turn blue paper red.
Litmus paper can be purchased at some gardening stores or on-line and it is inexpensive. You will need red and blue strips and for 100 of each, it should cost no more than $5.00. Test soaps, foods, skin, saliva, water in a pet’s bowl, blood from a meat product removed from packaging materials, household cleaning products, personal hygiene products (toothpaste, shampoo)…Your child can check any number of substances, but should keep a table of results. Keep litmus paper around for other future investigations of rocks.
Other opportunities to measure abound in conducting the following experiments or simply cooking with these substances. Measure amounts with measuring spoons or cups. Weigh those amounts (subtracting the weight of the measurement tool).
Discuss measurement concepts, such as more or less. Is there more or less of a reaction.
Time your experiments or after adding the vinegar or baking soda, how much time elapses before a reaction begins? How long does the reaction last?
Count the number of oranges, lemons or limes you purchase.
(Please note that mixing acids and bases can result in chemical reactions that spit or sputter, sending the acid into the air. If you have goggles or glasses your child can wear, then this should be encouraged when taking a closer look at what is occurring. If not, observe from a distance. These are not dangerous reactions, but precaution should be exercised.)
Measure some baking soda (a base) into a cup. (Baking powder can be used also, but it contains an agent that reduces its reactions with an acid). You can vary the amounts, and repeat the experiment. That is, your child can start with a tablespoon of baking soda, and then increase the amount with each successive experiment. Next, pour some white vinegar onto the baking soda and watch what happens. The same concept applies in terms of varying the amounts with each experiment. You and your child should do this on a surface that won’t stain or on newspaper or in a sink. Now watch what happens? Ask your child to articulate what she is seeing, or what is happening (Hint: this is a typical chemical reaction in which the acid and base produce a new chemical or a salt. The bubbles are full of carbon dioxide, or a gas is released.)
Variations on this experiment include:
- Measuring different amounts of base, acid or both before combining and noting the difference in the strength or intensity of the reaction.
- Substituting lemon, lime or orange juice for the vinegar. How do these substances react with the baking soda and is there a difference?
- Substituting cider or balsamic vinegar for white vinegar.
- Trying the same experiment with ingredients used in baking, such as milk combined with the baking powder. How about yogurt, sour cream or buttermilk? Try a dab of honey or molasses. What happens?
- Add the vinegar first, followed by the baking soda. Which method produces the most bubbles (adding baking soda first or after the acid)?
- Pour some vinegar into an old wine bottle. Add the baking soda and put the cork loosely into the top. Watch as the cork pops off! Alternatively, place the baking soda into a balloon. Carefully place the balloon over the mouth of the bottle. Once it is securely on, release the baking soda from the balloon into the vinegar that is in the bottle. Ask what your child thinks is happening.
- Add food coloring to the vinegar for fun!
- Add dish soap to the vinegar, then add the baking soda.
This is the same chemical reaction that the common “volcano” experiment capitalizes on. You can find this experiment on several sites or in books describing science experiments. It involves mixing baking soda and vinegar, but doing so in a built up model of a volcano. Call me a purist, but I don’t like to leave the impression that molten bubbling up from the earth’s crust is related to an acid-base reaction.
Your child might have questions about the fizzing or bubbles that resulted from mixing the baking soda and vinegar. Here is an extension to explore the nature of the gas or carbon dioxide, that resulted. Sprinkle baking soda onto a flame/heat proof dish (just not a paper plate). Set a small candle (a votive will do – but the smaller the better) in the middle of the dish. Light the candle. Next, carefully pour about a quarter of a cup of vinegar on the baking soda. This is the same experiment as above, but this time, pay attention to what happens to the candle. Hint: The candle needs oxygen to burn. The carbon dioxide that is produced from the chemical reaction is heavier than the oxygen and displaces the oxygen, thus depriving the lit candle of the fuel it needs to burn.
Find several tarnished pennies, or pennies that are dirty. Pour about 10 tablespoons of lemon juice (or vinegar) into the cup, add a pinch of salt, and then add a penny (or pennies) and swirl the solution around. The vinegar/salt solution loosens the copper oxide, which was responsible for the tarnish on the pennies. The penny should look shiny when removed from the solution (and rinsed with water).
Repeat this experiment with other liquids thought to be an acid such as soda or coffee. It may take longer to “clean” a penny with other acidic liquids so leave them overnight. Hint: The phosphoric acid in soda cleans the pennies.
Create edible acids. Squeeze lemon juice and taste. Add water (keeping track of measurement), until it is tolerable or the acid is less strong. Add a sweetener to taste (sugar, confectioner’s sugar, honey). If you like, add baking soda (dissolved in the water) so this lemonade has a fizz. As a child, one of my favorite foods involved sticking a porous peppermint stick into the center of a lemon cut in half. Sucking the juice through the peppermint straw results in a delicious, sweetened peppermint lemonade. Yum!
We discussed litmus paper above as an indicator of the pH content of a substance. Here is another method. Boil some red cabbage. First, ask your child to help grate the cabbage or separate the leaves apart. Place the cabbage in a pot and cover it with water then boil it until it is tender. Remove the cabbage from the pot. It can be consumed at this point if you like. Add butter.
Strain the remaining cooking water. This bluish solution is what you can use to test for acids and bases. Place the substances you are interested in testing in small jars or on saucers, then place a drop of the cabbage cooking water, using an eye dropper or a drinking straw (dip the straw into the cabbage cooking water, place your finger over the other end, and remove your finger when ready to release the solution). If the cabbage-water turns red, you have an acid. If it turns blue, you have a base. Keep track of these tests and compare with results of using the litmus paper.
With any remaining cabbage-water, add some vinegar and watch what happens. Mix some baking soda with water and add that to the cabbage water with the vinegar. There should be yet another color change.
Experiment with a pinch of the spice turmeric. Drop a pinch of turmeric on a known acid or base based on previous experiments. What happens?
Open a bottle of brown-colored soda (or pour some into a small container with a top) and then add 2% milk until it has reached the top of the bottle or smaller container). Replace the cap on the bottle (or top of the container) and wait. Observe and record the results over time. What is happening? (Hint: the phosphoric acid in the soda is reacting with the milk molecules. These separate out because they are more dense. Both milk and soda are acidic, but the soda is more acidic than milk. The phosphoric acid in soda essentially curdles the milk creating a solid.) Please discard the mixture when you are finished and do NOT drink.
In a glass jar add one cup water and one cup vinegar. Add food coloring if you like for fun. Then add 1 tablespoon baking soda. Quickly add different kinds of food and describe and observe what happens to them. Consider adding popcorn kernels, raisins, dried beans, or items that will not disintegrate in the liquid. Watch them over time.
Add about ¼ cup of vinegar to a jar. Next, add about the same amount of oil. If you are going to consume this as a salad dressing, choose nice tasting oil such as a virgin olive oil. Ask your child to place a top on the jar (or plastic container) and shake it. Predict and then discuss what happens? Now wait a couple of minutes and look again. Hint: The oil and vinegar should have separated back out and into separate looking liquids. To help the oil and vinegar stay together, there are several substances you can add that create an emulsion. On separate occasions, add paprika, mustard, a little cream, or some mayonnaise, and shake the jar. Now wait. Do the oil and water separate back out? Once the dressing is thick, consider adding other items to make a delicious salad dressing, or salt and pepper, chopped shallots, or any number of fresh or dried herbs. You can also vary the recipe using different types of vinegar (balsamic, cider, champagne). Over time, your child will become the family’s salad expert, and may actually enjoy eating vegetables if he is the chef.
Make pickles using an acid. Boil for ten minutes a combination of 1 cup of white vinegar (distilled), 1 tablespoon of salt, and 2 cups of sugar. Place 6 cups of sliced cucumbers and 1 cup of sliced onions in a bowl and pour the liquid over them. Place in sterilized jars or store in the refrigerator and consume!
After these experiments ask, no expect, that your child will help to clean up. Watch how she handles some of the concoctions she has created as they could be hot or messy. But also make sure that tasting does not extend to every solution. Tasting happens only when you have been asked and granted permission.
A possible extension of your exploration of acids is to discuss what role they play in our health. Stomach or gastric acids are critical for breaking down our food. But they can act up creating gas or cramps. Amino acids are part of proteins and play a role in metabolism. As we’ve noted throughout, many acids are dangerous (in car batteries) and can seriously comprise health, so take some time to discuss and explore health risks.
By this point, your child knows what he thinks about acids he has tasted. Do pets or other animals have the same reaction? If you have a pet, determine its reaction to lemon juice. I love my pets and wouldn’t go further than one test as I’m not sure it is right to insult their senses beyond the first test. If you think this is an appropriate experiment, you may want to set rules with your child. For example, the only acid you will test is lemon juice, and it will only happen once. Ask your child to observe the pet’s reaction. Do their mouths pucker the same way as ours?
Create a small puddle of lemon juice near an ant hill. How do the ants respond? Set some sugar water nearby how do they respond?
Explore where vinegar comes from or how it is made. What other foods result from fermentation?
Read about medicinal uses of vinegar. Vinegar is the result of fermentation. What other foods or beverages result from this process?
Give family members a taste of an acid (lemon juice) or a base (salt water). Take a picture of their faces in reaction to the taste. Share those photos with others and see if they can tell what that person just tasted, something sour or bitter.
Take a family poll of which salad dressing your child creates is the best or most liked and least liked. Create a bar graph.
Read food labels and generate a list of acids.
Explore other scientific terms you have most likely used in testing acids and bases: