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Fascinating Science Experiments for Young People
By George Barr, Mildred Waltrip
Dover Publications, Inc.Copyright © 1989 George Barr
All rights reserved.
Getting Off to a Good Start
You can easily get reliable results in your experimental work if you try to develop certain work habits. It is fun to do the research. But it is still more satisfying to feel that your conclusions are accurate. You can get this feeling of confidence by developing a good technique for attacking a problem.
Do you know exactly what you wish to find out? If you cannot pin-point your problem, you will find yourself repeatedly getting off the main track.
Even before you start your experiment, have you found out as much as you can about your problem? It may save you much time, money, and energy. It will also help you observe things in a more meaningful way. Go to library books, speak to experts and authorities such as curators of museums. By the way, it is good to work with a friend who shares your interests.
Do you have everything you need? If not, try to use inexpensive substitutes. It is very useful to have a work place at home with some basic tools and supplies. Work neatly, safely, and orderly. Put things back when you are through with them.
Can you foresee certain difficulties and avoid them? Plan your research. Can you think of better ways of performing parts of the experiment than those which are given here?
Report accurately what you see and always be on the alert for unexpected happenings. These may lead you to new problems to investigate later. In this way you will experience the thrills of a research scientist. Louis Pasteur stated, "Chance favors the prepared mind."
Learn to take readable notes in an organized manner. Become familiar with the use of tables and graphs. Do not trust your memory — and always label bottles! Also, write reminders to yourself, and tape these to parts of your experiment.
It is not scientific to base a conclusion upon only one experiment. Gather as much evidence as you can by repeating the experiment many times. If possible, do it in different ways. Think of possible sources of error. Invite your friends' criticism. Remember that an experiment does not always turn out as expected. Trying to discover why an experiment "failed" can often be more interesting than doing proven experiments. This is when your ability as a scientist is really tested.
You have no doubt heard of a CONTROL which is often used in an experiment. It is an important part of your research work which enables you to make very accurate comparisons before and after the experiment.
Wherever possible, you should have another setup just like the one on which you are working. All the conditions for both must be exactly the same, except for the one thing that you are doing differently to the experimental one. It is like setting up two experiments with just one difference between them.
This technique, used by scientists all over the world, lets you compare one thing at a time. You do not have to guess why any change occurred. Of course, not all experiments call for the use of controls. But keep on the lookout throughout this book for places where you can add controls — even where the specific suggestions may not have been included. They will improve your procedure.
For example, suppose you wish to find out whether a certain weed-killing chemical will kill dandelions in a lawn. Pour the weed killer on some dandelions, and in due time the plants die. Is this a good experiment? Of course not, because somebody may ask the obvious question, "How do you know that these dandelions died because of the weed killer? Maybe it was the time of year when most dandelions die anyway. Perhaps it was the lack of water that killed them."
A scientific control should be set up consisting of a nearby group of dandelions of similar size and health. These will not receive the weed killer. Otherwise, all the other conditions should be identical — amount of sunlight, temperature, moisture, type of soil, etc.
Now, if the treated dandelions should die, but those in your controlled group remain healthy, you can be more positive about your conclusion that it was the weed killer alone that killed them.CHAPTER 2
How can you separate colored solutions?
Have you ever watched a motion-picture scene of a chemist at work in his laboratory? Everything certainly looks mysterious and complicated. You get the feeling that it takes many years of special training and practice to know this business.
Sometimes, however, even a highly skilled chemist may use a method which is extremely simple and, at the same time, very effective. Would you like to be a scientific detective and do something that the best chemist could do years ago only after many hours of patient work? By learning a simple technique, you can do the same thing in minutes.
Suppose you want to find out whether a certain colored solution contains just one colored substance or whether there are several colored materials dissolved in it? Does this sound impossible? Well, you can do it. Just make a dot of the solution on a folded strip of white blotting paper, about 1 inch from the end. (See illustration.) After the dot dries, stand the blotting paper in a covered quart-size jar containing about ½ inch of water. The colored dot should be about ½ inch above the water.
In a short time the water will creep up the blotter and start dissolving the colored dot. The dissolved colored material in the dot continues to rise until it is redeposited on the paper. You may notice that there is now a separation of colors. For example, a bluish layer may be distinctly visible above a red layer. Perhaps a small mixed area may separate the red and the blue sections. Of course, if the original solution consisted of a single substance in water its color would not change this way.
This method of identifying and separating colors which are in solution is known as PAPER CHROMATOGRAPHY (krome-uh-TOC-ruh-fee). The word comes from chroma which means "color" and graphy meaning "writing." The colored paper strip is called a CHROMATOGRAM. In a way, it represents the fingerprints of the substance.
This technique works on the principle that molecules of different substances travel up the blotting paper at different speeds. The greater the attraction between the blotter and the molecules, the more slowly the molecules rise.
In your experimentation with this fascinating color analyzer you can use only colored substances which are soluble in water, since that is what you have in the jar. Chemists, of course, may use alcohol, benzene, or other dissolving agents. Examples of common water soluble, colored substances you may have at home are: washable ink, red ink, Mercurochrome, laundry bluing, food coloring dyes used for Easter eggs, strong tea, red cabbage, instant coffee, tobacco, ketchup, beet juice, merthiolate antiseptic. No doubt, you will discover more when you start your search.
Make a separate chromatogram for each material you intend to use. These individual strips will act as CONTROLS. By knowing the colors shown by individual substances, then you should be better able to distinguish them when they separate from a mixed solution.
Use white blotting paper, 1-inch wide and about 7-inches high. Make a heavy pencil line down the center and fold along this line as shown in the illustration. This shape will prevent the paper from bending in the jar. Keep the jar covered, since this creates a humid atmosphere so that the colored solution does not dry on its way up the strip.
To make the dots, use the end of a wooden match or a broken toothpick. Dip this into the solution and then touch the blotting paper. The size of the dot should be a little less than ¼ inch in diameter. However, if you wish, you may make a horizontal line instead of a dot.
For your first analysis, make three separate strips. One should have a dot of only red ink. Another strip should have a dot of washable blue ink. The dot on the third strip of blotting paper is obtained from a mixture of several drops of red ink and blue ink prepared in a small dish. Use a pencil to label each strip. Write on the folded side not being used for the test.
For other experiments, mix several substances having distinctive colors. Study the separations by comparing with your controls. Keep good records.
Try using filter paper, or even paper toweling strips, for paper chromatography. You can attach the top of the paper strip to the bottom of the jar cover by means of cellophane tape. If the paper curls, the bottom can be weighted by means of a small paper clip.
Chromatography is often used in crime detection because it gives quick and reliable results. When you learn more about this method of analysis, you will find that it is not limited to colors alone. We used colors for our beginning experiments because it is more convenient and visible. When invisible separations of molecules occur in colorless mixtures, the chemist has ways of developing the strips with chemicals so that different colors appear.
Can you make a tester for acids and bases?
Anyone who has ever worked with a chemistry set has used litmus paper to test for an acid or a base. Litmus paper is inexpensive and can be purchased from any drugstore. It consists of an absorbent paper which contains a natural dye obtained from a lichen, which is a kind of a plant described on page 108. There are two kinds of litmus paper, blue and red.
When blue litmus paper is placed in an acid solution it turns red. When red litmus is placed in a base it turns blue. Of course, you know that there are strong acids such as nitric acid and sulfuric acid which can eat away metal, cloth, and shoe leather. However, your home contains many safe acids such as acetic acid in vinegar, citric acid in lemons, and lactic acid in sour milk. The sour taste of many foods is due to acids.
When red litmus is placed in a solution containing a base, it turns blue. A base may be considered a chemical opposite of an acid. In fact, you can neutralize, or weaken an acid by adding a base to it. In the same way, a base can be weakened when an acid is added to it. Bases usually have a bitter taste and feel soapy when rubbed between the fingers. You have many substances at home which are basic, among them are household ammonia, milk of magnesia, and bicarbonate of soda. Bases are also referred to as ALKALIS (AL-kuh-lize).
Touch a moist bit of the food to be tested with the litmus paper. If solutions are used, it is better to employ test tubes. These can be bought in the drugstore. You may also use small glasses, pill vials, or even the glass containers in which toothbrushes are often purchased.
Litmus is called an INDICATOR because it indicates whether something is an acid or a base. It is only one of many natural substances which possess different colors in acids and in bases. You can experiment with the following easily obtainable materials to make your own indicators:
Red cabbage, tea, rhubarb stalks, diluted grape juice, purple blossoms of hollyhocks, red or purple dahlias, purple iris, red petunias, violets, cherries, huckleberries, elderberries. In addition you might try any colored juices from flowers, fruits, or vegetables to discover new indicators of your own.
In general, the procedure is to squeeze, crush, stir, and shake the fibers in some hot water until the water takes on a color. Then see how a small amount of the liquid behaves when either an acid or a base is added to it. The most common household acid for this purpose is vinegar. To test the indicators' reaction to bases, use several drops of household ammonia water or a pinch of baking soda. Finally, bottle your indicators and label them.
For example, here is how red cabbage is converted into an indicator: Chop up a few of the most purple leaves. Boil in a small amount of water for about twenty minutes. Use a small flame. Do not burn by allowing water to boil off. Cool. The liquid is now purple. Bottle some of this and label it: CABBAGE (NEUTRAL).
To a portion of the remaining purple liquid, add just enough baking soda to turn the liquid green. Bottle this and label it: CABBAGE (BASIC). To the last portion of purple liquid, add just enough vinegar to make it turn red. Bottle this and label it: CABBAGE (ACID).
To test whether some unknown liquid is an acid or a base, pour a small amount of the indicator in a test tube. To this, add some of the unknown liquid. Record what happens.
How would each of the three cabbage indicators behave with a substance such as milk of magnesia which is a base? The neutral cabbage will change from purple to green. The acid cabbage will change from red to green. The basic cabbage will not be affected. (Actually, the neutral cabbage indicator is unnecessary. It was included here because of the fun in seeing the color change.)
Do you think you can make paper indicators by soaking blotting paper or mimeograph paper in the indicators and then drying them?
Remember that many substances are not acids or bases. They are neutral. Of course, if they are very weak acids or bases and your indicator is not sensitive, then you will also get a neutral reaction.
Test the following substances: orange, lemon, lime, grape, tomato, onion, celery, grapefruit, rhubarb, soda water of any flavor, table salt, chlorine water used for laundering clothes, apple, banana, milk, benzene, vinegar, sour milk, cottage cheese, alcohol, human perspiration, aspirin, epsom salt, starch, washing soda, plaster, pickle, baking powder, vitamin C pill, borax, boric acid, strong laundry soap, lime water, mayonnaise, French dressing.
Use this form for your notes:
Can you formulate your own tooth paste?
Many years ago our country was not industrialized and there were no corner drugstores, supermarkets or department stores. Most families had to prepare their own food, design and construct furniture, and weave and sew clothing. In addition, many of the household preparations had to be developed after much experimentation. People proudly talked about their personal formulas for soaps, medicines, and even shoe polish.
You too can have something to be proud of by developing your own inexpensive tooth powder which you and your family will be happy to use. You will also gain much interesting experience as an amateur pharmacist.
Despite the advertisements which appear everywhere, dentists agree that most tooth pastes and tooth powders serve the same purpose, regardless of price. Their main job is to cause a mild, harmless scouring action which brushes away the particles of food clinging to the teeth.
It is believed that cavities are formed when bacteria use the food particles of especially sugars and starches to produce acids which dissolve away the hard, protective enamel of the teeth.
The following formulas and suggestions are for your experimentation. Mix very small amounts for each trial recipe. Vary the quantities of each ingredient until you have a product which is not too gritty, leaves a pleasant taste, and makes the teeth feel clean. When you are finally satisfied, then you may mix up a larger quantity.
Store each product in a folded piece of wax paper which is properly labeled and secured with a rubber band. Keep careful notes of each experiment.
Your first recipe for a tooth powder is one recommended by dentists as being economical and very effective. It consists of 1 part table salt and 3 parts baking soda, which is also known as bicarbonate of soda. These ingredients are found in every home. Try fine salt in one formula, then use coarse salt in another. You will get accustomed to the salty taste which is easily swished away by several mouthfuls of water.
Another type of tooth powder has a more pleasant taste and enables you to do more experimentation. You will have to purchase a small quantity of powdered chalk from your druggist. This is also known as precipitated chalk and is very inexpensive. Start your experiment with small amounts of the following formula:
4 parts of precipitated chalk
1 part baking soda
1 part powdered sugar
(Use a very small thimble as a measurer of "1 part.")
In making up different proportions of each ingredient you should know that the chalk is used for its scouring action, while the baking soda is added mainly for counteracting the acids in the mouth. The sugar is included only to provide a pleasant taste, so use it sparingly. Try using a small amount of saccharin as a substitute for the sugar.
You may wish to add a small quantity of powdered white soap. This is what makes commercial tooth powders foam slightly.
If you want a flavor, add a few drops of oil of peppermint, wintergreen, cinnamon, or vanilla. You can get tiny amounts of these from your druggist.
When you find the best combination for the tooth powder you can make a tooth paste from it. Make up a solution of equal parts of glycerine and water. Mix this solution with the powder in a deep bowl until a smooth, thick paste is formed.
You can use milk of magnesia instead of the baking soda as an acid neutralizer, if you wish. You can keep the tooth paste in a jar.
CHEMISTRY — More to find out: How are secret invisible messages written?
"Invisible ink" can be made from certain household liquids such as onion juice, lemon juice, or milk. Use any one of these to write a message on white paper, with a very clean pen point. You can see what you are writing if you place a light on your left side and look at the writing from the right. Dip the pen into the juice often. Do not scratch the paper. The writing should be invisible when dry.
To read the message, it is necessary to char the writing. Try heating with an electric iron or baking in an oven for a few minutes.
The writing appears because the solids in the juices burn or char faster than the paper does. Experiment with many juices.
What cleans pennies?
Place a tarnished copper penny in a small drinking glass and squeeze some lemon juice over the coin. Does the penny get clean? Pour some table salt into the glass. In a few minutes the penny will be as bright as new. The cleansing action is due to hydrochloric acid which is formed from salt and the citric acid in the lemon juice.
Will salt alone clean pennies? Can other household acids be used with the salt instead of lemon juice? Try vinegar; it contains acetic acid. Can rust be cleaned this way? Can you clean nickels and dimes too?
Excerpted from Fascinating Science Experiments for Young People by George Barr, Mildred Waltrip. Copyright © 1989 George Barr. Excerpted by permission of Dover Publications, Inc..
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