I’ve pulled another STEM activity out of my lesson plan files for you this week. This activity gives kids hands on experience in identifying acids and bases. This is my full lesson plan for this class so please excuse the treachery wording. I unfortunately don’t have access to any of the photos that go with this plan. I hope you enjoy doing this lesson and activity.
Materials to Make Indicator Solution
- Head of Red Cabbage
- Kitchen Knife
- Hot Water
- Container with a lid (I used a gallon juice container)
Materials for Experiment
- Small Paper Cups or portion cups
- Eye droppers
- Lemon Juice
- Water (tap, distilled or filtered)
- Baking Soda
- Saucers or small bowls (perfect world have three bowls per group)
Preparation (Adult to Prepare)
- Cut the head of cabbage into quarters and cut into strips with a kitchen knife.
- Pour hot water over the shredded cabbage, push the cabbage down with your hands, or spoon, ensuring it is covered in water. I used a kettle to heat the water.
- Let stand for three hours.
- The chemicals that color the cabbage will dissolve, turning the water purple.
- Strain the purple liquid into a gallon juice container, or other storage container, let cool in the refrigerator with no lid. Once cooled place a lid on the container.
- Refrigerate the liquid when not in use.
To identify liquids as an acid or a base using an indicator solution.
Fill up each small bowl or plastic cup with the following items. Each group will get one of each.
Baking Soda, one spoon full
Water (tap, distilled, or filtered)
Ensure you prep enough for each group.
Ensure all containers / equipment are clean and dry.
What is chemistry? (Give students an opportunity to answer)
- Chemistry is the branch of science that deals with the identification of substances which matter is composed.
- The investigation of their properties and the ways in which they interact, combine and change, and the use of these properties to form new substances.
What are the scientist called who study chemistry? (Give students the opportunity to answer)
What is an acid and a base? (Give students an opportunity to answer)
- An acid or acidic solution has a high concentration of hydrogen ions, greater than pure water.
- A base or basic solution has a low hydrogen concentration, less than pure water.
- And just for fun, pure water is neutral. Which means it is neither an acid or a base.
- Chemists use the pH scale to measure how acidic or basic a liquid is. The scale measures values from zero to fourteen.
- Acids are found from seven to fourteen.
- Bases are found from zero to seven.
- Distilled water is a seven, which means it is neutral.
Today we are going to determine if certain liquids are an acid or a base.
When chemists mix different chemicals or liquids together the liquids may change color. Through this color change chemist can learn more about the content of different liquids. They call the solution that changes color the indicator. We will be using an indicator today made out of cabbage juice.
Hold up the container for the students to see. Give a brief description on how you made the indicator solution.
Each group will receive small cups containing:
Cabbage Juice, lemon juice, plain water and a spoonful of baking soda.
One eye dropper
Saucer, short plastic cup or small bowl
- Have one student in the group drip a few drops of cabbage juice onto the saucer.
- Then have the next student add a few drops of lemon juice.
- The indicator will turn red, or pinkish.
- The lemon juice contains citric acid, and the chemical in the cabbage juice reacts with the acid turning it red.
- Most liquids that taste sour are acids, but chemists can’t taste liquids by tasting them.
- Why do you think that is? (Give students an opportunity to answer)
Some liquids are poisonous.
- Have a student, from each group, wash out their saucer.
- Have a student mix the water and baking soda together.
- Have another student drip a few drops of the cabbage juice into the saucer and then add a little bit of the baking soda solution.
- This time the indicator will turn green.
- The baking soda, or sodium bicarbonate, is a base. Which is the opposite of an acid.
- Wash the saucer again.
- Wash out the eye dropper.
- Now place some water (tap or distilled) in the saucer.
- Have a student drip a few drops of the cabbage juice into the water. What happens? The indicator doesn’t change color because water is neither an acid or a base, but neutral.
Additional liquids you can test, if so desired.
- Strong Tea
- Orange Juice
- Ginger Ale
Once your students have completed these experiments they will understand the difference between an acid and a base, what Chemists do and general chemistry terminology.
Depending on age and maturity, select a helper or two to help with clean up.
- Collect all the containers
- Carefully pour out the remaining liquids
- Clean containers thoroughly , air dry if possible, if not dry by using a single use paper towel. This reduces the chance of contaminants.
As always, please follow me on Instagram @beinglaurakmarshall
Until next time.