Make Litmus Solution

Here is a familiar science lesson. I include it here because it correlates nicely with a previous lesson about using alkali to process corn. An alkali is a caustic or corrosive substance such as lye or powdered lime that is added to soil. As a caustic substance, it can help break down the coatings on corn. As lime, it helps lower or neutralize the acid in some soils. Thus, two important uses of alkalies are to break down difficult material, or to react with acids.

A gentle alkali is baking soda. A dangerous alkali is lye. The difference between the two is their position on the pH scale. The pH scale rates the acidity or alkalinity of a material. High pH can burn your skin and mucous membranes. Low pH can be used in baking. But how do you know the pH of a substance? Litmus paper, purchased at lab supply stores or some garden centers, will give you a reading. However, you can make your own litmus solution. This lesson shows you how.

Commercial litmus paper is soaked in a solution of water and lichen species. When you dip the paper into a liquid to be tested, the paper changes color. Match the color with the key that comes with the litmus paper and you’ll discover the pH value, ranging from 0 to 14. Low numbers are for acids, high numbers are alkali, 7 is neutral. The more extreme the number, the higher the acidity or alkalinity. Different litmus papers have different color values, but the numbers are standard.

Here is a simple pH scale:

Make Your Own Litmus Solution or Paper

Chop or tear leaves of purple cabbage. Put into a large pot and cover with water. (Note: the water source could make a difference. Tap water is generally neutral, which is what you want. Well water may start off being alkaline or acidic, which will affect the results of your homemade pH test.) Bring the water to a boil; then allow it to cool. Strain out the cabbage leaves and discard. Keep the water, which will be blue. This is your litmus solution.

Distribute the solution among several clear glasses. Keep one for comparison. This will be your “neutral”, unchanged solution and it represents #7 on the pH scale. Add a small amount of a substance you wish to test, into each of the other cups and stir. The color will change due to the acidity or alkalinity of each substance. Pink to deep red are acid; green to yellow are alkaline, also known as “basic.” Arrange the cups in order of color on each side of the neutral cup and you have your own litmus color scale. Be sure to label each cup.

From left: vinegar, orange juice, neutral, hardwood ash, calcium hydroxide, lye

Make litmus paper

Soak paper towel strips in the solution and allow them to dry. The color changes are not as dramatic as the litmus solution. You can drop liquids onto the paper, or dip the paper into liquids you want to test. If you want to test a powder, or soil, mix it with water first. Again, make sure your water is neutral.

Standardizing your tests

It is impossible to be completely accurate with the cabbage juice indicator, but you can approximate the standard pH test. Test the items on the standard test (graphic above) and note the color you get with the cabbage juice indicator. Either take a photo of your solution and then write the pH number on the photograph, or try to match the color with crayons/colored pencils. Keep these for future reference.

Don’t be limited by the items on the standard pH scale! Try all sorts of powders and liquids you find around your house. So much fun!

An experiment that didn’t turn out the way we anticipated (but we learned something important):

I taught this subject to a group of Kabul university chemistry students. The class was held in a hotel conference center. I instructed students to get a large pot of boiling water from the hotel kitchen. The hotel kitchen had just finished serving lunch to students and staff. Students were delighted to learn they could make their own litmus solution because litmus paper was difficult to come by, but purple cabbage was readily available from street vendors. The indicator solution was rapidly made, but the test colors kept coming out wrong. Everything was testing too alkaline. I decided the human dishwashers in the kitchen hadn’t rinsed the pot sufficiently after washing. It still had soap residue in it, which is alkaline. I was somewhat insulting of their care in rinsing pots and thought ruefully of the lunch we had just eaten, cooked in those same pots. Then it occurred to me that the well water serving the kitchen – and all of Kabul – might be alkaline itself. I checked this with local geologists who told me that the famously good Kabul water came from wells sunk deep into limestone layers. The limestone filters the water but adds alkali to it. Then I asked a physician whether this could be a cause of kidney stones that many residents had. “Yes,” he said. “Alkaline water can cause them.”

Chocolate Chip Levers

OK, the title is click-bait. You don’t need to use chocolate chips in this lesson but they sure are fun. I have used pennies or even beans. You simply need small objects that are consistent in weight and don’t roll.

Age level: PreK – third grade
Science Standards: for space considerations, these are addressed at the end
Materials Needed: 12-inch or cm rulers, tape, chocolate chips (or lentils, pennies, metal nuts, beans)

Levers are simple machines. That means they use few or no moving parts and can be the basis of more complex machines. Levers have been used since antiquity to lift or balance objects. In this lesson we will study teeter-totters and their kin to understand how they can be used to lift heavy objects with little effort.

Ancient Assyrians lift a stone colossus using a lever


Identify the parts of the lever: lever arms and fulcrum. The position of the fulcrum is crucial. In the following drawing, the fulcrum is in the middle and two children of equal size balance each other. But what if one child is much larger than the other one? Or, a child wants to teeter-totter with her mother who weighs quite a bit more? In those cases, the small child might not be able to lift the larger person and the teeter-totter wouldn’t work. Think: How can this problem be solved? As students provide thoughts, ask them to draw their solutions on the board. Think about this question as you proceed through the lesson. Either the fulcrum must be moved, or the position of the people on the teeter arms must change (effectively changing the fulcrum) The teacher may or may not want to share the correct solution at this point.

One child lifts another

Capturing student interest

Show photos of extraordinary levers at work, or levers that went awry. Or provide a discordant event (see “Fun with Students”, below)

Street scene, Kabul, Afghanistan

The Activity

In this lesson, we will create a teeter-totter from a ruler; then use it to lift objects of unequal weights.

Step 1: Tape a 6-sided pencil firmly to a table.

Step 2: Balance a ruler atop the pencil. You have created a potential lever. Where are the lever arms? Where is the fulcrum? The ruler is 12 inches long. Where should you place the ruler so it is balanced on the pencil?

The ruler is balanced on a pencil fulcrum

Step 3: Only after the pencil is balanced (both ends off the table), give the students two chocolate chips. Place one chip on each end of the ruler-lever and rebalance it. Make sure the two ends are off the table. Ask students to note the length of each lever arm (6 inches and 6 inches)

Success at balancing one against one

Step 4: Only after the two chips are balanced, give the children an extra chip. Ask them how they can change things so that a single chip can balance (or lift) two chips. Tell them they must keep the chips on the end of the ruler (because you want to emphasize the position of the fulcrum and lengths of lever arms). The single chip should be on the “zero” end of the ruler for easier computation. Students should note the lengths of each lever arm.

Step 5: After students have discovered they can change the lengths of the lever arms, give them 3 more chips and ask them to balance a single chip against 5 chips. Remember to leave the single chip on the zero end and keep all chips as close as possible to the end of the rulers.

Working to balance 5 chips against 1

Assessment and Thinking

What did you do, to enable a single chip to lift 5 chips? (made that side longer). Point out that longer levers do more work than shorter levers. Another way of thinking: Pushing on the end of a lever provides more strength than pushing midway on the arm. Some manufactured levers are designed to remind you where to push.

The end of the nail clipper is marked

Who can draw a teeter-totter correctly to enable Jane and her mom to use it?

How could you correct the situation of the poor donkey and his cart (above?) Lengthen the cart arms and put the donkey at the head.

Could an ant conceivably lift an elephant on a teeter-totter? How would you do it and why would it work?

The Elephant and the Ant

Fun with students via a discordant event

Rigging the game. Before asking students to start the lesson, I make one of two rigged rulers:

Rulers painted unevenly, difference magnified for clarity
  • Use red and black poster paint to paint one ruler in two equal 6-inch segments. Paint a second ruler in the same colors but make one end longer – hopefully, not enough for students to notice on casual inspection. The line separating the two colors will be put on the fulcrum. Use the first ruler to demonstrate how to balance one chip against the other. Switch out the second ruler while distracting them. Then use a “super chip” from a special jar to lift more than one chip. Ask students to explain.
  • Use a regular ruler to balance two chips. Then switch that ruler with an identical one that has a penny taped to the bottom. In one case, a chip balances another chip. In the second case, with everything apparently the same, one chip will simply not balance the other chip. Ask students to figure it out. Note that unscrupulous merchants have rigged scales this way in the past. With modern laws and computerized scales this normally wouldn’t be a problem today.
Preschool children share a laugh at rigged ruler

Etching of Assyrians and levers; Nineveh and Babylon – a narrative of a second expedition to Assyria during the years 1849, 1850, and 1851 by Sir Austen Henry Layard 1874

Donkey cart in Kabul; photographer known, google photos

Nail Clipper:

All other photos and drawings are owned and copyrighted by Camilla Barry, 2020

This lesson addresses many Next Generation core standards that carry through grade levels PreK – 12. Examples are (but not limited to):
Look for pattern and order in observations
Compare attributes of objects through measurement
Reason abstractly and quantitatively
Model with mathematics, Compare numbers
Use materials and tools to solve a specific problem
Analyze Data
Plan and Conduct an Experiment
Recall and gather information to answer a question
A problem can be solved through engineering
Multiple solutions to a problem are possible and should be compared/analyzed