Chemistry

pH and Cabbage Juice

Grades K-5 (with variations)

Overview:

We are going to use the juice from a cooked red cabbage to test the pH of many household items.

The more acidic the solution is the more red it will turn when the cabbage juice is added. If it is neutral it will be purple and if it is alkaline then it will be green/blue. Colors are very brilliant and the kids love to try testing and mixing different solutions.

Time:

30-45 min

Materials:

For the groups:

Cabbage Juice

Test Solutions- Lemon Juice, Ammonia, Baking Soda mixed with water, Vinegar, Seltzer Water, Laundry Detergent mixed with water, Borax mixed with water, Plain Water, clear soda

Small Containers for test solutions

Droppers (in cabbage juice)

Litmus Papers

Crayons for observation notes

pH Testing worksheet for each student

Demo materials:

“Acid in the Eye”

HCl - hydrochloric acid

Petri dish

Egg

“Bromothymol Blue Breath Test

Bromothymol Blue pH indicator

Straw

Dry ice nuggets

Small test tube

Safety glasses

“Dry Ice and Cabbage Juice”

Cabbage Juice

Large (100mL) graduated cylinder

Cup of dry ice nuggets

“Magic Kleenex Flower”

Kleenex

Pipe cleaners

Phenolphthalein (pH indicator)

Spray bottle

Windex

Setup:

Shred the cabbage and add enough water to cover it. Boil for 20-30 min- long enough for the water to turn dark purple. Strain the cabbage, collect the juice, and allow it to cool. One head of cabbage makes about 1 gal of juice, which starts to stink after a couple of days. The cabbage keeps better than the juice, so if you want to spread this out over a couple of weeks, you may want to make a couple of batches. Keep juice refrigerated or it will spoil. *Or shred and add equal amount of hot water to a blender. Then blend and strain.

You can make the solution the night before, or you can have the kids help you shred the cabbage and make the solution.

Pour test solutions in small containers

Label the small containers

Set out one set of test solutions for each group

Prepare 0.2 wt% phenolphthalein solution: either dilute the premixed solution or dissolve phenolphthalein salts in alcohol to correct concentration

Background:

Acids and bases are related to the number of hydrogen ions present in a solution based on the Brønsted-Lowry definition. Acids increase the concentration of hydrogen ions and bases decrease the concentration by accepting the ions.

Sören Sörensen came up with the pH scale, which measures the acidity on a scale from

0-14.

0- Most acidic like HCl

7- Neutral like Pure water

14-Alkaline like NaOH

|---------------------------------------------|----------------------------------------------|

1	Acid (Acidic)	7	Base (alkaline)	14

Neutral

To test an acid or base you can use an indicator like litmus paper, which generally turns pink when dipped into an acid and blue when dipped into a base.

Red cabbage juice is another indicator. Red cabbage contains pigments call anthocyanins. The pigments give it the red/purplish color. Anthocyanins belong to group of chemical compounds called flavonoids.

For most pH indicators, the compound acquires a proton at low pH (lots of H+) but loses it at higher pH. This seemingly minor alteration is sufficient to alter the wavelengths of light reflected by the compound, thus creating the color change with respect to pH. Anthocyanins behave somewhat inversely in that the pigments "gain" an -OH at basic pH, but loose it at acidic pH.

Activities/procedure:

First test each solution with litmus paper and record the pH on the worksheets

Drop the cabbage juice into each test solution, until the solution changes color. Record this data on the worksheets.

Organize the solutions from most Acidic (red) to most Basic (green/yellow)

Compare findings to other groups

When done, invite the students to mix the solutions slowly and see what happens to the color!

Demos:

“Acid in the Eye”

“Bromothymol blue Breath Test”

“Dry Ice and Cabbage Juice”

“Magic Kleenex Flower”

Make a flower out of Kleenex and spray it with a phenolphthalein mixture. When sprayed with a base (Windex or ammonia work great) the flower will turn pink. When it dries, it goes back to white. You can to this over and over!

Discussion:

Talk about the pH scale (pH is a measure of the hydrogen concentration.)

Which substances were acidic?

Which were basic?

Which was the most acidic/basic?

Was there a chemical reaction between the cabbage juice and the substance?

How to we know a chemical reaction happened?

Discuss the four ways to identify that a chemical reaction has occurred. This is a color changing reaction.

Vocabulary:

Acidic (Acid)

Alkaline (Base)

Chemical reaction

Neutralization

pH scale

References:

http://www.visionlearning.com/library/module_viewer.php?mid=58

http://chemistry.about.com/library/weekly/aa012803a.htm

http://www.madsci.org/experiments/archive/859332497.Ch.html

Engineering

Cup Pyramid Challenge

Grades K-5 (with variations)

Overview:

Time:

Materials:

Setup:

Background:

Activities/procedure:

Discussion:

Vocabulary:

Engineering

Spiral & Human Knot

Grades K-5 (with variations)

Overview:

Time:

Materials:

Setup:

Background:

Activities/procedure:

Discussion:

Vocabulary:

References:

Matter Matters

Cartesian Diver Demonstration

Grades K-5 (with variations)

Overview:

Time:

Materials:

Setup:

Background:

Activities/procedure:

Discussion:

Vocabulary:

References:

Matter Matters

Crushing Can Demonstration

Grades K-5 (with variations)

Overview:

Time:

Materials:

Setup:

Background:

Activities/procedure:

Discussion:

Vocabulary:

References:

Matter Matters

Water Whirlpool Demonstration

Grades K-5 (with variations)

Overview:

Time:

Materials:

Setup:

Background:

Activities/procedure:

Discussion:

Vocabulary:

References:

Polymers

Plastic Exploration

Grades K-5 (with variations)

Overview:

In this activity students learn about the different types of recyclable plastics, their unique properties, and how to identify them.

Time: 30 minutes

Materials:

For the class:

Pieces of different recyclable plastics numbers 1 through 7 (about 4 pieces per student)

For each student:

Plastics Exploration worksheet

Setup:

Spread the recyclables across many tables. Make sure there are multiple samples of each of the seven types.

Polymers

Grow Dinos

Grades K-5 (with variations)

Overview:

This activity teaches students about careful scientific procedure and measuring. Students get their own grow dinosaur, made of a super absorbent polymer, to measure and study the rate of growth.

Time: 30-40 minutes every day

Materials:

For the class:

Water

Rulers

For each student:

Plastic grow dino (available at toy stores)

Clear plastic clamshell container labeled with his or her name

Worksheet for daily observations

Labeled graph for plotting growth

Teaching/demo materials:

Overhead projector

Labeled graph on an overhead for plotting group data

Setup:

Give each student his or her own grow dino and a plastic clamshell container (or cup). Be sure the students know what each dino is called in order to avoid confusion while reporting data. We had a Triceratops, a Tyrannosaurus Rex, a Dimetrodon and an Apatosaurus (a long-neck or one time Brontosaurus) Provide a ruler for each student for measuring their dinos. It is a good idea to practice using a ruler with the class and to talk about what all of the marks mean. Depending on age, some kids have had little practice with measuring, fractional pieces or the metric system. Since each of these can be a considerable skill to master, make allowances throughout the lesson and just have the kids work at their skill level.

Polymers

Gel Beads

Grades K-5 (with variations)

Overview:

In this activity, students get to combine two liquids- one colored, one clear. When they drop the colored solution into the clear solution, it forms a bead of gel that can be examined. It is a fun and colorful way to teach students about polymers, crosslinks, and diffusion.

Time: 40 minutes

Materials:

For the class:

Sodium alginate (2 wt% in water) in jars colored with food coloring

Calcium chloride (1.5 wt% in water)

Droppers

Small strainers to remove gel beads from solution

For each student:

Small plastic dish

Small baggies for them to take home their beads

Setup:

Place four jars of sodium alginate (one of each color) on each table with droppers for each jar. Provide a dish of calcium chloride for each student.