Last session the experiments involved making clay float, the diving eyedropper, air pressure, and the baking soda/vinegar fire extinguisher. This session will explore science with a little more thought provoking demonstrations.
Experiment 1. Blue plus clear equals red???
Materials: Red cabbage, vinegar, baking soda, sauce pan, small bowls, misc. kitchen items.Step 1. Remove 5-6- cabbage leaves and chop. Place in a sauce pan, cover with water and cook for 5-10 minutes. Cool and strain the blue juice into a pitcher or bottle.
Step 2. Arrange 3 small bowls or drinking glasses (white or clear glass are best) and pour a quantity of the blue juice into each bowl.
Step 3. Into bowl one sprinkle a small amount of baking soda. Observe that the color darkens, in addition it will take on a blue-greenish color.. Into bowl two slowly pour a small quantity of vinegar. Observe that the color changes to a lighter blue then to pink. Bowl or glass three receives no treatment but serves as a reference color. In addition to testing baking soda and vinegar, testing other household items such as coke, stomach anti-acid tablets (Tums), or soaps, can give interesting and surprising results.
Lesson: You have just performed a science lab experiment to detect the acid or base properties of a liquid! Scientists use the term pH to measure the chemical balance of a substance. In simple terms acid things taste sour and base things taste bitter. Caution children to never taste unknown substances to discover their properties!
Technical discussion: A scale from 1 to 14 is used to measure pH. Seven is neutral with 1 being extremely acid and 14 being extremely base. Indicators are methods to visualize the level of acid or base. Litmus strips are small pieces of paper that will change color depending on the pH of the substance being tested. Red cabbage contains a substance similar to that found in litmus paper. Garden soil test kits are available to determine if your soil is good for acid or base loving plants. Here are the pHs of ten common items. Lye =14 (used in soap manufacture), ammonia water = 11.6, baking soda = 8.0, human blood = about 7.4, pure water = 7.0, bread = about 5.5, sour milk = 4.4, vinegar = about 2.9, battery acid (sulfuric) = 0.3.
Technical discussion for older kids: The pH scale of 1-14 is not linear. In other words, the interval between 3 and 4 is not the same size as the interval between 4 and 5. In fact the intervals increase by ten times with each step! This curious property is found in many areas of nature. Our ears are sensitive to sounds in a similar manner. Sounds must actually be four times louder to sound twice as loud. (Called the decibel scale). Our eyes respond to the brightness of light likewise. Objects appearing twice as bright are actually four times brighter. Even musical scales reflect a non-linear property. The pitch change (in frequency between B and C is different than the pitch change between E and F.
Super bonus points: The pH scale is based on logarithms. In 1614 John Napier, a Scotsman, published a system to simplify the task of multiplying large numbers. Today virtually all modern branches of physical science use logarithms to deal with extremely large or small numbers. Go to Wikipedia.org for a detailed discussion.
Experiment 2. Cloud in a jar.
Materials: Large clear plastic flexible jar (bottle). My favorite is a 64oz. juice bottle. The mouth is large enough to draw in the smoke needed and the rectangular shape is easy to hold. Be sure to remove the label so you can see the cloud! Wearing a dark shirt as you hold the bottle in front of you will make the cloud more apparent to your viewers. Water, matches. Again, here is an experiment that requires flame or heat. Adult supervision required!
Step 1. Add about ½ half cup of water and tighten the cap. Shake vigorously. (No cloud) Squeeze and repeat. (No cloud).
Step 2. Carefully light one match and allow it to burn for a few seconds. With the cap off the bottle slightly squeeze it and place it below the match. Extinguish the match. The match will smoke for a few seconds. Try to get some smoke into the bottle by relaxing your grip to help the bottle “inhale” a little smoke. It is not necessary to capture all the smoke but more is better than less. If a little smoke is visible in the bottle it’s OK but a surprisingly little will do the trick.
Step 3. Replace the cap and shake vigorously while squeezing. Stop shaking and quickly relax your grip. Fog (cloud) will appear in the bottle. Squeeze the bottle and the cloud will disappear. Relax your grip and it will reappear!
Step 4. Take a bow.
Lesson: This simple experiment belies the multiple physical phenomena occurring. The three principles involved are: first, the compression of a gas heats it while expansion cools it; secondly, evaporation and condensation of water into air is dependent on temperature; and thirdly, water molecules, when grouped together will disturb the passage of light. Step one simply captured the evaporating water molecules and raised the relative humidity in the bottle to near 100%. Even the second part of step one, squeezing the bottle while shaking, caused the humidity to equal or even exceed 100%. Still no cloud! Why? Condensation, to occur, needs a little help. If the humidity is raised enough the water molecules will begin to condense on each other. Cooling, in effect, raises the humidity because colder air slows down molecular activity, thus forcing the water molecules to squeeze together. Adding smoke particles create a “seed effect” that speeds up condensation by providing a nucleus to begin the process.
Outside the bottle, in the sky, there are generally ample condensation nuclei in the form of dirt, smoke, pollen, dust, salt crystals, etc. to serve this purpose. Water vapor is constantly being added to the atmosphere from oceans and lakes. Plants and animals contribute vast amounts of water vapor too! So, what causes the cooling? Our atmosphere is in constant motion, in addition to heat being added by the sun and being lost to space. On a typical summer day the sun heats the ground causing the air to lift to higher altitudes. These rising columns of air, (called thermals) as they lift themselves, expand due to lower atmospheric pressure as they rise. Basic laws of gas behavior explain that lowering the pressure of a gas while changing nothing else will result in cooling. In fact, on average, as air is lifted it will cool 3.5 degrees Fahrenheit per thousand feet! Airliners fly at altitudes where the air temperature is often below zero even on a summer day.
As moisture laden air reaches a certain altitude the temperature reaches a point where it can no longer support invisible water vapor. Condensation occurs (called the dew point temperature) and a visible cloud forms. The flat bottoms of cumulus clouds marks the altitude/temperature tipping point where the invisible becomes visible! Warm and cold fronts, mountain ranges, high and low pressure areas, and other physical causes can and do cause cloud formation. Oh, yes, what about rain? That’s a whole story in itself. Check out any book on basic meteorology or Google “How it works.” for great explanations.
A Personal Note
People occasionally ask me if I was a science teacher. The answer is no. Although I created a special course at our High School on Aviation & Aeronautics. Obviously I have acquired a fair understanding of things scientific. My professional career was in public education in student services (counseling). I have always had a curiosity about what “made things tick”. Hobbies in electronics and aviation exposed me to many aspects of science and stimulated further study.
Today’s youth are swamped in a pop culture that emphasizes materialism, and instant gratification. To be fair, many youth do show concern for our fellow man and the environment. For me, my volunteer time, sharing my enthusiasm and curiosity for science and learning, has been very rewarding. I encourage all parents and grandparents to discover the joy of youth’s natural curiosity and foster their love for the infinite variety and beauty of creation.
Paul Lupton (Park Place 2012)