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Last week, we shared our top-5 favorite summer science activities you can do with friends and family. Today, we’re diving head-first into one of them (fizzy lemonade!) to give you the nitty-gritty on how the science creates the magic! Grab your safety goggles and apron—it’s time for chemistry 101: acids and bases.
Last week’s experiment, making fizzy lemonade, had you combine an acid (lemon juice) with a base (baking soda), and the chemical reaction that followed created delicious carbonated lemonade (with the addition of sugar, of course). This week, we’re exploring the properties of acids and bases, learning how to check if a substance is an acid or a base, and sharing a hands-on activity in which you can create your own acid/base indicator using red cabbage!
Scientists identify acids and bases along a scale called the pH scale—the H stands for “hydrogen”; however, the p has been known to stand for “puissance” (French), “Potenz” (German), and “power” (English).
The colorful image below illustrates the pH scale from acids to alkali (alkali are bases that dissolve in water), with examples at each pH level.
When compared, acids and bases act and appear opposite in many ways. With a pH value of less than 7, acids are corrosive in nature. Acids taste sour, and their smell can burn your nose. Additionally, acids can feel sticky to the touch. Contrastingly, bases have a pH of greater than 7, react with many oils and fats, taste bitter, typically do not have a smell (with the exception of ammonia!), and have a slippery or soapy texture.
Acid-base indicators change color in response to different pH values. Litmus paper and pH paper are used for quick, relatively imprecise measurements. There are two types of litmus paper available that can be used to identify acids and bases—red litmus paper and blue litmus paper. When dipped into a liquid, blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions.
pH paper, on the other hand, is used to determine if a solution is acidic, basic, or neutral, and, like litmus paper, this is determined by dipping part of the paper into a solution and watching the color change. The packages that pH paper comes in often includes a color-coded scale indicating the pH that something has when the paper turns a certain color.
While litmus paper is easy enough to obtain (see links in previous paragraph), you can also make your own acid-base indicator right in your kitchen, which you can use to test all kinds of at-home solutions(with adult supervision, of course). Red cabbage juice is considered to be an indicator because it shows us something about the chemical composition of other substances.
So grab your safety gear and head over to your nearest grocery store to the produce section and grab a head of red cabbage! (Well, maybe you don’t need your safety gear just yet).
Note: This activity requires adult supervision.
Ingredients: red cabbage
Supplies: safety goggles, apron, sharp knife (please ask for help from an adult), pot to boil water in (or blender), strainer or colander, glass bowl, clear cups or glasses, household liquids to test (vinegar, baking soda, coffee, juices, soaps, bleach, and anything else you want!), something to stir with
Ask an adult to help you cut off about 2 to 3 cups (the amount doesn’t need to be exact, but the more cabbage, the more indicator you will get).
Have an adult boil a pot of water and place the cabbage pieces in. Bring the water back to a boil for a couple minutes. Turn heat off and let sit for at least 10 minutes, until the water becomes a reddish-purple color. (You can also place the cabbage in a blender with water).
Strain the water out into a glass bowl and let cool.
Once it has cooled, pour some into clear cups or glasses and add different liquids to test.
Gently stir or swirl the solution—what do you see happen?!
As you can see, the purple cabbage juice turns red when it mixes with something acidic and turns green when it mixes with something basic.
Why does this happen? Red cabbage contains a water-soluble pigment called anthocyanin that changes color when it is mixed with an acid or a base. Anthocyanin turns red in acidic environments (those with a pH less than 7) and the pigment turns bluish-green in alkaline environments (those with a pH greater than 7).
When testing your solutions, ask yourself a few questions: Do all the acids or bases change the indicator the same color? What do you think this means? Does adding a larger quantity of an acid or base change the color more? Do you see any patterns in what the acids or bases are used for?
Suggestion for more science: Make your own indicator strips by soaking coffee filters cut into strips in the red cabbage juice, then letting them dry completely. Once dry, you can dip them into a liquid to test its pH. Or, check out this easy-to-use pH buffer calibration kit!