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DISCUSS:
This probably isn’t the first time you’ve heard the word "acid." What does this word make you think of?
Acid Test Results worksheet | 1 per student |
Acid Test Results Answer Key teacher-only resource | 1 per class |
Mixing Sheet printout | 1 per pair |
Testing & Acid Reaction Supply Mats printout | 1 per group |
Clean-up Supplies (Eg. Paper Towels)
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1 roll per class |
Purple Cabbage (Chopped)
You can use 7 ounces dried black beans instead, but purple cabbage works better.
|
Details
2 cups per class
|
Table Covering (eg. Trash Bags)
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2 bags per group |
1 Acid
You can use lemonade, ketchup, mustard, pickle juice, or yogurt.
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Details
1 tablespoon per group
|
Baking Powder
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1 tablespoon per group |
Baking Soda
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1 tablespoon per group |
Coffee Stirrers
Craft sticks or spoons will also work.
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Details
4 sticks per group
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Dixie Cups (3 oz)
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7 cups per group |
Measuring Cup
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1 cup per class |
Measuring Spoons
|
1 set per class |
Plastic Bin
Must hold at least 4 cups of water. Used to make your indicator liquid.
You can also use a gallon-sized Ziploc bag.
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Details
1 bin per class
|
Plastic Straws (Not Bendable)
|
5 straws per 8 students |
Salt
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1 cup per class |
Sheet Protector
You can also use taped-down waxed paper or Press n' Seal.
|
Details
1 per pair
|
Toothpicks
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2 toothpicks per pair |
White Vinegar
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2 tablespoons per group |
You will need access to water for this activity.
We suggest students work in pairs and two pairs of students share supplies at the same table group. Homeschool students can work on their own.
If you’re using purple cabbage, put 2 cups of chopped cabbage in 1½ cups of water. Leave it for at least an hour, stirring occasionally. The cabbage will turn the water purple. Drain the chopped cabbage and reserve the purplish-pink liquid. If you’re using black beans, put 1 cup of beans into 2 cups of water and leave them for at least an hour. The beans will soak up some water and turn the rest purplish brown. Drain the beans and reserve the purplish-brown liquid.
Cut each straw in half to make two short straws. Students will use these to transfer drops of liquid. (Full-length straws are likely to tip over cups.)
Gather all of your Dixie cups and separate them into seven equal piles. You will fill the cups in each of these piles with a different liquid or powder.
We recommend you set up four supply stations.
Station A: Acid Reaction Supplies
From this station, each group of students will bring the following back to their desk:
Station B: Testing Supplies
From this station, each group of students will bring the following back to their desk:
Station C: Worksheets & Clean-up Supplies
From this station, each pair of students will bring the following back to their desk:
Station D: Unknowns
From this station, each pair of students will bring the following back to their desk:
The purple liquid that you prepare from the cabbage (or black beans) is called an indicator. There’s a pigment in purple cabbage and black beans that changes color when it reacts with an acid or base. You and your students should notice that the color of the liquid changes to a reddish/pink when you add it to any of the acids (e.g. vinegar). You can then use this information to test unknown liquids. If the liquid turns pink, then it’s an acid.
You and your students will also notice that when baking soda is mixed with vinegar, there is fizzing that indicates an acid-base reaction. But baking soda does not fizz when mixed with water, making it a good acid indicator. Baking powder will also fizz with vinegar. But you will notice that baking powder will also slightly fizz when water is added. This is because baking powder is actually a mixture of baking soda (base) and cream of tartar (acid). This is why it reacts with both water and vinegar. So baking powder is not a good indicator because it fizzes when any liquid is added.
Student slideshow: English | Spanish
Teacher printout: English & Spanish
In this reading, students learn the story of a chemical reaction that caused a huge molasses tank to explode in Boston in 1919.
For a limited time, view archived reading extensions here.
Pigments in purple cabbage and black beans change color in acid. This list from Thought.Co. suggests other natural color-changing pigments to experiment with.
Here are three of our favorites:
This is one of our favorite activities. You start with an ordinary chicken egg. Leave it in vinegar overnight & the acid dissolves the eggshell. You end up with a egg that’s held together by the flexible membrane inside the shell.
You’ll find detailed instructions on how to make a “naked egg” on the Exploratorium’s Science of Cooking website.
You’ve seen that adding baking soda to acid makes it fizz. Here is an activity that uses fizz to make tasty treats.
New Zealand’s Science Kids explain how to make fizzy lemonade.
Who knew science could be so tasty?
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