Cabbage Chemistry: a pH Indicator
What you'll need:
-lemon juice (an acid)
-ammonia (a base)
-other liquid samples (soda, vinegar, water, milk, etc.)
The measure of a substance's acidity is labeled pH. The pH scale is a chart that organizes pH levels from 0 (acidic) to 14 (basic) with 7 being neutral. Strong acids are low on the scale, while strong bases like ammonia are much higher. Pure water is right in the middle.
Indicators are solutions that change color in the presence of acids or bases. Red cabbage juice contains a natural indicator that can be used to determine a substance's pH.
*****WARNING***** This experiment involves heat and household chemicals. Always get help from an adult before beginning an experiment like this!
To make the indicator, chop up half of a head of red cabbage into roughly 1 inch or smaller pieces. Boil these in a pan of water until a purple juice is created. Strain the juice into a container. This juice is your indicator.
To test the indicator's reaction to acid, pour a sample of the indicator into a clear glass. Add some lemon juice and observe the color change. This is how the indicator reacts to acid.
To test the indicator's reaction to a base, pour a sample of the indicator into another clear glass. Add some ammonia and observe the color change. This is how the indicator reacts to a base.
Next, try the same procedure with other liquids (milk, soda, vinegar, juice, soap, water, etc.) and observe their reactions. Thicker liquids might need to be stirred in. You will be able to compare the colors to the previous examples (lemon juice and ammonia) and determine if the substance is an acid or a base. The intensity of the color also indicates how strong of an acid or base the substance is.
This simple experiment will give you an insight into the world of chemistry. Testing the pH of substances is a useful skill in many areas, from soil and water management to commercial product testing.
Simple Slimy Slime
What you'll need:
-Borax powder (available at most stores near the laundry soap)
-disposable spoons or stirrers
Polymers are chains of linked molecules. In the experiment below, the Borax powder will cause the molecules in the glue to link and form a "slime" that can be played with.
*****WARNING*****Keep chemicals away from your eyes! Safety glasses are recommended. Do not eat or even taste any of the chemicals.
There are many "recipes" available for this activity, but this one works well and is easy to clean up. Larger quantities can be made by increasing the amounts of the ingredients.
Dissolve one teaspoon of Borax in a cup of water to create a Borax solution. In the second cup, mix about an inch of glue with 3 tablespoons of water and stir. Add your favorite color of food coloring to the glue mixture.
Next, add a tablespoon of the Borax solution to the glue solution. As you stir, the slime should form! When it is mixed, take it out and see how it feels. You should find that it has properties of both a solid and a liquid.
This simple demonstration makes a fun, messy polymer. You can change the ratio of Borax to glue to create thicker or thinner slimes. The slime can be stored in a sealed plastic bag, and should be kept away from small children. DO NOT EAT THE SLIME!
Crushing a Can...with Air Pressure!
What you'll need:
-a soda can
-a pair of tongs that will lift the can
Although it is invisible, air and other gases have mass. They also exert pressure on anything they touch. This pressure is greatly affected by temperature. Warm gases tend to expand, and cold gases tend to contract. This experiment will provide a dramatic demonstration of this effect.
*****WARNING***** Safety glasses are recommended. Extreme safety should be exercised around the stove. An adult should supervise this experiment. Beware of the steam produced by the can, because it can cause burns.
First, prepare an ice water bath. A metal pan, such as a cake pan, is recommended. Any heat resistant pan will work. It should hold at least an inch of cold water and be large enough to stand the soda can in it.
Next, you will put a small amount of water in the bottom of the soda can. The quantity isn't important, so around a half inch of water is fine. Too much takes too long to boil, and too litle boils away. When you have the can ready, place it on a stove burner and adjust the heat to high to boil the water. Be careful not to tip the can over or let the steam touch your skin.
When a steady stream of steam is coming out of the can, carefully grab it with the tongs. Quickly and carefully turn the can upside down and set it in the water bath. You should see dramatic results.
When you boil the water, hot water vapor is produced. This vapor expands and fills the can. When you put the can in the cold water, the vapor cools and contracts. The water also creates a seal on the opening of the can. This rapid drop in temperature creates a rapid drop in pressure, which causes the can to implode. This can also be done on a large scale with a 55 gallon drum.
More fun experiments coming soon!