In the Classroom

  • PK – grade 3 students: Instead of making them a juice try showing how different things around them are an acid or base.

Science Discipline

Chemistry

Topics

Acid and bases, pH indicators

Activity Title

Rainbow Juice

Materials

  1. 1 scoop Red Cabbage Powder (for each thing you are going to test)
  2. 50 mL Water (for each thing you are going to test)
  3. Acidic things: Lemon juice, Orange juice, Vinegar
  4. Basic things: Soap, Baking Soda
  5. Clear cups (enough for each thing you are going to test)

Procedure

  1. First give some background on acids and bases to the children. You can use the Explanation section below. Ask them the questions below during your demonstration.
  2. In each cup combine 50 mL of water and 1 scoop of red cabbage powder.
  3. Add the first thing you are going to test in your first cup.
  4. Continue with each thing you want to test.

Questions

  1. What color do you think it will turn? Red, Blue, or purple?
  2. What color did it turn? Red, Blue, or purple?
  3. What does this color change mean? Remember why red cabbage changes color.
  4. Was your guess correct?

Explanation

How does a lemon taste? It taste sour. Lemons have a chemical called vitamin C which is an acid. This acid is the reason lemons are sour. Acids are sour. If something has an acid then something called its pH will be low. The pH will be higher if very little acid is present. Red cabbage juice can be used to see how much acid is in something. If there is acid the red cabbage juice will turn red. A base, like soap can make there be less acid. When something has lots of base in it, it turns the red cabbage juice blue or green. Some things do not have any base or any acid. These things are neutral and turn the red cabbage juice purple.

Next Generation Science Standards

2-PS1-1. Plan and conduct an investigation to describe and classify different kinds of materials by their observable properties. [Clarification Statement: Observations could include color, texture, hardness, and flexibility. Patterns could include the similar properties that different materials share.]
  • Grade 4 – 6 students: For an in class demonstration I would recommend the well-known acid-base reaction of baking soda and vinegar in the presence of the pH indicator made by the red cabbage.

 

Science Discipline

Chemistry

Topics

Acid and bases, pH indicators

Activity Title

Rainbow Juice

Materials

  1. 1 scoop Red Cabbage Powder (for each thing you’re going to test)
  2. 50 mL Water (for each thing you’re going to test)
  3. Vinegar
  4. Baking Soda
  5. A clear cup

Procedure

    1. First give some background on acids and bases to the children. You can use the Explanation section below. During your demonstration ask the questions below.
    2. In the cup combine 50 mL of water and 1 scoop of red cabbage powder.
    3. Add a good amount of vinegar to your cup, probably half full.
    4. Now slowly add baking soda, maybe using a teaspoon, so that the students could see the color change and solution will not foam up to much.
    5. Try to get it to change from red to blue or green if you can.

Questions

  1. What color do you think it will change when I add the vinegar?
  2. What color do you think it will change when I start adding baking soda? What if I add more baking soda?
  3. Which is the acid and which is the base?

Explanation

A pH indicator is something that changes color when mixed with a substance depending on that substance’s acidity. Red Cabbage can become a pH indicator when boiled in water. If you cook red cabbage in hot water you end up with a purple liquid showing that the water is neutral in its acidity. When you add lemon juice, which is an acid, to the indicator solution it turns slightly red and gets redder if you add more. An acid makes the pH low. If you then mix in a base like baking soda, the liquid turns blue and eventually green when you add even more baking soda. A base makes the pH high.

(http://www.qldscienceteachers.com/junior-science/chemistry/acids-and-bases)

(https://www.youtube.com/watch?v=I18K2upEHLc) 

Next Generation Science Standards

5-PS1-4. Conduct an investigation to determine whether the mixing of two or more substances results in new substances.
  • Middle school students: The well-known acid-base reaction of baking soda and vinegar in the presence of the pH indicator made by the red cabbage is a good way to present students with this topic.

Science Discipline

Chemistry

Topics

Acid and bases, pH indicators

Activity Title

Rainbow Juice

Materials (needed for each group of 2-3 students)

  1. 1 scoop Red Cabbage Powder (for each thing you are going to test)
  2. 50 mL Water (for each thing you are going to test)
  3. Vinegar
  4. Baking Soda
  5. A clear cup

Procedure

First give some background on acids and bases to the children. You can use the Explanation section below. Have students answer the following questions before and during the experiment.

Instruct students to do the following:

  1. In the cup combine 50 mL of water and 1 scoop of red cabbage powder.
  2. Add a good amount of vinegar to your cup, probably half full.
  3. Now slowly add baking soda, maybe using a teaspoon, so that you could see the color change and solution won’t foam up to much.
  4. Try to get it to change from red to blue or green if you can.

Questions

Before the experiment:

  1. What color do you think the solution will change when the vinegar is added?
  2. What color do you think it will change when you start adding baking soda? What if you add more baking soda?
  3. Which do you think is the acid and which is the base?

During the experiment:

  1. What color did the solution change when the vinegar was added?
  2. What color did it change when you started adding baking soda? What happened when you added more baking soda?
  3. Which was the acid and which was the base?

Explanation

A pH indicator is something that changes color when mixed with an acid—like citric acid or vinegar–or a base—like baking soda or soap. When an acid is mixed in water it forms a solution of hydrogen ions (H+); however, when bases are mixed into water they form a solution of hydroxide ions (OH). Red Cabbage is one of many kinds of pH indicators. If you cook red cabbage in hot water you end up with a purple liquid showing that the water is neutral. This mix is your pH indicator. When you add an acid to the indicator solution it lowers the pH and the indicator turns slightly red and gets redder if you add more acid because of the high concentration of hydrogen ions. If you then mix in a base like baking soda the pH goes up and the liquid turns blue and eventually green when you add even more baking soda because of the high concentration of hydroxide ions. Adding baking soda to an acidic solution also results in bubbles of carbon dioxide gas that result from a chemical reaction between hydrogen ions and bicarbonate ions from the baking soda.

(http://www.qldscienceteachers.com/junior-science/chemistry/acids-and-bases)

(http://chemistry.about.com/od/acidsbase1/a/red-cabbage-ph-indicator.htm)

(https://www.youtube.com/watch?v=I18K2upEHLc)

Next Generation Science Standards

MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.  [Clarification Statement: Examples of reactions could include burning sugar or steel wool, fat reacting with sodium hydroxide, and mixing zinc with hydrogen chloride.] [Assessment boundary: Assessment is limited to analysis of the following properties: density, melting point, boiling point, solubility, flammability, and odor.]