Indicators, taking on one color or another, helped us distinguish an acid from a base. For example, vinegar from ammonia. But often this is not enough. How, say, to distinguish one acid from another? For this very important purpose, chemists have come up with and tested many reactions, perhaps for all more or less common substances. Such reactions are always noticeable by something; they allow one or another substance to be immediately and unmistakably determined by some sign. This sign is very often the color.

One color reaction that helps identify one common substance you're already familiar with: the starch found in many plants turns blue in the presence of a tiny additive, even traces of iodine. Unfortunately, this is a rare case, and most chemical analyzes require substances that you probably cannot buy anywhere. However, there are some things you can think of...

Here, let's say, ammonia, an aqueous solution of which, ammonia, you have already bought in a pharmacy. How to find ammonia? Firstly, by smell: once you smell it, you will remember it forever. Yes, but it is not always convenient to sniff (and sometimes it is simply impossible). Then - color reaction.

Throw a few grains of copper sulphate into a glass or a bottle of water and stir well. The solution should be pale blue; if it turns out to be dark, dilute it with water. Pour a little ammonia into this pale blue liquid. The solution will immediately turn bright blue. It was ammonia, combined with copper sulphate, that formed such a bright substance. And gave himself away with his head.

Another reaction is also with blue vitriol. Prepare a solution in a glass, but not as pale as before, but bright blue (that is, take more copper sulfate). Put unnecessary iron objects in it - at least old nails or screws, but not rusty ones. And take care of some other things, however, sometimes looking at the mortar with nails. After some time, you will notice that the solution has turned from blue to green. And when you take the nails out of it (but not with your fingers, but with tweezers or at least a clothespin - this is a general rule for all chemical cases), you will see that they have become copper-red.

When the nails lay in blue vitriol, iron gradually displaced copper from it and took its place. The result is green iron sulfate. And where was the displaced copper to go? Is that to settle right on the nail. Which she did, covering the nail with a red copper film.

To recognize certain substances, chemists test them with fire. The trick here is that many simple substances that are part of complex substances (for example, copper - in blue vitriol, calcium - in calcium chloride) have the ability to color the flame.

And not in the same color, but in a variety of colors.

If you have a spirit lamp at home, you can use it. And you can take a candle. But in any case, do the experiment only with adults - no jokes with fire! And be careful: there should not be paper, rags and any other things that easily catch fire nearby.

Find a soft wire, preferably nichrome - this wire is used to make spirals of electric stoves, irons, etc. Of course, you don’t need to break the tile or iron for this; a burnt-out spiral from an old electrical appliance will do just fine. As a last resort, buy the cheapest coil at the electrical store.

Straighten a not very long piece of the spiral and fix it in some kind of holder: for example, wind one end of the wire around a pencil or clamp it in a clothespin. At the other end, make a small loop with a diameter of no more than half a centimeter. Heat the loop on the fire and lower it into a glass of clean water - this is necessary so that the wire becomes clean, without impurities that can distort the whole picture. Do this several times until the flame stops changing colors as the wire is introduced.

Take a little table salt - the same one in the salt shaker; its chemical name is sodium chloride. Mix salt with an equal amount of ammonia (ammonium chloride). Please do not confuse ammonia with ammonia: the first is a white powder used for soldering, so it is sold in hardware stores; the second is a liquid with a pungent odor. In our experience, as in soldering, ammonia cleans the wire and helps the salt to evaporate quickly.

In a mixture of salt and ammonia, drop two or three drops of water, dip a wire loop and bring it into the flame. It will immediately turn bright yellow. This is how it reacts to sodium. To be honest, even small amounts of sodium make the flame turn yellow, and one could not make any special preparations for this experiment: it is enough just to "salt" the flame. But in all other cases, careful preparation is highly desirable: not all substances act on the flame so vigorously.

The next substance may be calcium chloride. If you have powder, do with it the same way as described above. If liquid, dip the cleaned loop directly into it. Calcium colors the flame bright red, but the trouble is that such substances rarely do without sodium impurities, and as a result, the yellow color suppresses the characteristic red. Therefore, it would be good to stock up on blue glass (or blue sunglasses) and look at the flame through it: blue glass traps yellow rays. By the way, this is also useful when looking at a flame with other substances - and an admixture of sodium compounds is not excluded in them.

The same experiment, not forgetting to clean the wire with fire and water each time, repeat with blue vitriol and with three substances that you can buy at the pharmacy: potassium chloride, zinc oxide and boric acid (this acid is solid, it is sold in powder form) . Look and write down, just in case, how the color of the flame changes substances, which include potassium, zinc and boron. And in these experiments, if the flame is yellow because of the admixture of sodium, take a blue filter.

Let's deal with miracles of a different kind. If before you had coloration, now it will disappear.

Drip a small amount of blue fountain pen ink into a bottle of water to make the solution a pale blue. In the same vial, put a crushed tablet of activated charcoal. Close the mouth with your finger and shake the mixture. She brightens up before her eyes. The fact is that such coal literally absorbs dye molecules with its surface, removing them from the water. And when the colored substance is absorbed by the coal, it is, of course, no longer visible.

Try to make the same experiment with other coloring substances, for example, with inks of different colors and with gouache paints (but in all cases, take highly diluted solutions).

You will find that coal is capable of absorbing many substances.

This ability is not unique to coal. Some clays are called whitening clays. Wet chalk powder also absorbs paints (and therefore various contaminated objects are sometimes cleaned with chalk). You can experience how absorbing, absorbing dyes are scraps of blotting paper, scraps of old fabric, soil from a flower pot. Or, say, corn sticks. If you put a few sticks in a jar, into which you drop a drop of cologne in advance with a pipette, and then close the jar with a lid, then after ten minutes, when you open the lid, you will no longer smell: it was absorbed by the porous substance that makes up corn sticks. Such absorption - whether colors, smells - chemists call adsorption.

Let's go back to the color that we have appeared, changed and disappeared. Now it will move from one substance to another.

Pour about a third of water into a test tube or vial and add a dozen drops of iodine tincture to get a not very dark, brownish solution. Pour the same amount of gasoline over the solution (perhaps your family household has it, and if not, you will have to go to the hardware store).

When conducting this experiment, as well as any other in which gasoline and other combustible substances are involved, remember that there should not be a fire nearby - not a gas burner, not even a match!

After closing the vial with a cork, shake its contents well and leave it alone for a few minutes. Gasoline is lighter than water, so the mixture will separate: the water will remain at the bottom, and gasoline will float up - it does not mix with water. But, having set off on his way up, he will also take iodine with him, because iodine does not dissolve well in water, but well in gasoline. As a result, the lower, water, layer will be almost colorless, gasoline - dark brown.

Carefully, without stirring, drain the top, gasoline, layer into another vial, close it with a cork and leave it alone. In the meantime, prepare some fresh copper - such an experiment you made quite recently, immersing iron nails in a solution of copper sulfate. From a nail that has turned red in the solution, scrape off the plaque of just settled copper with an old spoon or some piece of iron. When a pinch of red wet powder is collected, pour it immediately into a vial of gasoline solution and close the cork again.

Now shake the vial several times and observe the color of the solution. After a minute or two, it will disappear, or at least become almost invisible. This iodine reacted with copper, and in this case a colorless compound was obtained - copper iodide.

The same experiment can be done with pieces of copper foil (it is similar to the silvery aluminum foil in which chocolate is wrapped, only reddish in color). However, in this case, the reaction will be much slower, and it will be necessary to shake the solution for several minutes before the color disappears.

What happened in the vial of iodine when gasoline was poured into it is scientifically called extraction. This is a very common technique, and not only in chemistry. With the help of solvents, they extract, extract the oil from sunflower seeds and nut kernels. And when the coffee beans are subjected to extraction, they get a brown liquid, from which the water is then evaporated, and the rest - a fluffy powder - is laid out in jars labeled "Instant Coffee".

Let's set up another experiment with extraction. This time we'll make the green colorless and the colorless green.

Fresh leaves of any plant will serve as a source of greenery for us: from lettuce to nettle. To speed things up, you can grind a sheet or two, but you can leave them untouched - as you like. Put them in a thin-walled glass (necessarily in a thin-walled one: thick, faceted, it can burst) and fill it with a small amount of diluted alcohol. You can take, say, a glass of vodka (such use of it - for chemical experiments - is, in my opinion, the most correct), or you can take cologne: it also contains alcohol. You probably already guessed what will happen next. But at room temperature, alcohol will take a long time to turn green. Therefore, put the glass in a saucepan with hot water (chemists call it a water bath), and it is advisable to put the glass not directly on the bottom, but on some wooden circle. When the water in the saucepan has cooled, remove the leaves from the glass with tweezers. They have discolored, and the alcohol has become emerald green. Do you know what we extracted from the leaves? Chlorophyll, a green dye that helps plants "feed" on solar energy.

Two useful conclusions can be drawn from this experience. Firstly, if you accidentally stained your knees with grass, then you can wipe them off with alcohol or cologne. Secondly, to decorate cakes, pies and other homemade sweets, green dye is often needed, which is harmless to humans. Now you know how to cook it. Alcohol will not hurt here, because the dye will need a few drops. But if you are extracting chlorophyll for food, then please do not take cologne and make sure that the leaves are edible and not bitter - lettuce, spinach, etc. Otherwise, you will get an onion-scented cream ...

Extraction, as you probably noticed, is based on the fact that different substances dissolve in different ways. Let's return to the example of coffee, which, by the way, is almost insoluble in cold water. Chicory dissolves much better. If you throw a little ground coffee with chicory into a bottle of cold water, you can see that part of the powder floats on the surface (this is coffee), and part dissolves and sinks down, leaving behind a brown trail (this, of course, is chicory).

A curious and often used method of recognizing and separating impurities is based on the ability of substances to dissolve differently in the same liquid. This method is called chromatography.

I hope you still have a solution of chlorophyll from green leaves. Now we will check whether this is a single substance or a mixture.

Take out a clean white blotting paper from the notebook (strictly speaking, and it has a scientific name - filter paper). Put it on glass or on a tile and put a drop of chlorophyll solution from a pipette in the middle. Wait until the stain blurs and drop a drop of alcohol into the middle (you can use isopropyl, it is used to clean glass and is sold under the name IPS). When the drop is absorbed, drop the next one; and so several times. The spot will get bigger and bigger, and two multi-colored rings are clearly visible on it: one is yellowish-green and the other is gray-green. These are two varieties of chlorophyll, both of them were in the leaves, and now they are separated on paper due to the fact that they dissolve differently in alcohol. Chemists call this method "paper chromatography"; they use a special porous paper, which, as you see, can be quite replaced with a blotting paper.

And here is another version of chromatography. Maybe it will be more accessible, since the solvent will be just pure water.

Cut out a strip of filter paper (that is, from a blotting paper) one or two fingers wide and at one of its ends, about a centimeter from the edge, draw a line with ink. Poke a hole at the other end of the strip, insert a stick or pencil into it and place it on the edges of a tall glass so that the strip is inside the glass, but does not touch the walls and almost reaches the bottom. Very carefully, so that the splashes do not fall on the paper strip, pour a little water down the side of the glass. As soon as the bottom edge of the strip is in the water, stop pouring water and carefully watch what happens next.

And this is what will happen: the water will rise up the paper. And let it rise until it reaches almost to the end. Then take the strip out of the glass and let it dry. You will see on it not one, but several dashes of different colors and at different heights. This is water, which serves as a solvent in the ink, so it dispersed various coloring substances across the paper.

I must say that ink of any color is rarely made from a single dye: much more often from a mixture. So you can test blue, red, green, and black inks, gouache paints, various fabric dyes (they are sold in hardware stores) and any other colored liquids, including juice and fruit water, in your home chromatograph.

It can also happen that pure water does not separate substances well. Then try other options, especially since the experience is simple and does not take much time. Try instead of water to take a mixture of equal amounts of water and vinegar - it will be an acidic solvent. Try the main solvent - two or three tablespoons of ammonia in a glass of water. You can, of course, take alcohol or isopropyl alcohol.

For chromatography, not only paper is used. Simple experiments can be done with starch. Shake two or three teaspoons of starch with a little isopropyl alcohol (IPA) or cologne, apply the liquid mixture to the glass and let dry. Then, on a dry plate, drop one drop of a colored substance, let it dry, apply a drop of alcohol and see how the stain spreads. If it was a mixture of substances, colored rings will appear. Try to separate some liquids from your first-aid kit in this way - say, valerian drops, cough mixture or calendula tincture.

And the last option for home use is with starch poured into a long transparent tube. Plug the lower end of the tube with cotton wool, pour a layer of starch about 10 cm high. Pour a little colored liquid (chlorophyll solution, diluted ink, juice, etc.) on top and, when it soaks the starch layer by half, add a little alcohol or other solvent. Beautiful multi-colored stripes will appear on white starch. Try to pick up different colored substances and different solvents. And in order not to get confused in the end, what happened as a result of these very serious experiments, write down the information you obtained in a notebook (preferably in the form of a table).

In general, I must say, you rightly consider yourself a young chemist, and every self-respecting chemist keeps a laboratory notebook (or journal) in which he writes down his observations and results of experiments. It's time for you to start such a laboratory journal. Write down in it what, when and how you did, what results you got, what conclusions you made for yourself. All this will take literally minutes, and it will give a lot of benefits and food for thought. Otherwise, why would adult experimenters waste time writing in journals?

After such a serious matter, let's take a break and do some colorful miracles just for fun. For them, it will be necessary to stock up on glass, but not ordinary, window glass, but liquid. There is such a substance - sodium silicate, its solution in water, thick and sticky, is called liquid glass. It is often used in construction; however, in everyday life too, but under a different name - silicate office glue. Perhaps, for our purpose, the glue is a little thick, so pour it into a small bottle and mix it in half with water. Keep in mind that liquid glass, as soon as it dries, cannot be peeled off by anything, and therefore, if you put a spot of silicate glue on a table or on clothes, wash it off with water and immediately. For the same reason, I do not advise you to stick photos in an album or drawings on the wall with such glue.

Pour into a test tube or vial about a third of pharmacy calcium chloride and drip a few drops of a solution of phenolphthalein. Pour about the same amount of diluted silicate glue into another vial. And now pour the contents of the first vial into the second and shake the mixture. Firstly, it will turn red and, secondly, it will thicken like jelly or jelly. Once again - the experience is just like a trick.

Another variant of the trick experiment with liquid glass: instead of calcium chloride, take two or three pinches of magnesium sulfate (it is sold in a pharmacy under the name of bitter salt, or Epsom salt) and throw it into a vial half filled with water. Shake, add three to four drops of diluted silicate glue and stir well. Again, jelly forms in the vial, only this time pale pink.

You can use your ability to get red jelly from colorless solutions to color pictures without paints and colored pencils. At least this way. Draw the outline of the drawing on a piece of paper with a pencil and “paint over” everything inside the outline with a transparent solution of phenolphthalein. Cover another sheet of paper entirely with diluted silicate glue. Fold both sheets, press one against the other and let them stay together for three to four minutes. Carefully separate the sheets - and you will see that the picture you have drawn has turned red by itself.

Making the invisible visible is not such a special miracle. There are many recipes for this, and all of them have been known for a very long time. For example, this: take ammonia powder on the tip of a spoon, pour it into a small bottle of water. The clear solution will serve as your ink. Dip a clean pen in it and write or draw something on plain writing paper. Let the paper dry properly, but do not even think of putting it in a warm place, say, on a battery, just to speed things up. Nothing is visible yet - after all, the solution was transparent.

Now let's heat up our piece of paper. So that it does not accidentally catch fire, it is best to heat it over an electric stove with a closed coil, holding the leaf with tweezers or a clothespin. If there is no such tile, you can heat it over a candle (or spirit lamp). However, paper with an invisible design must be held high enough above the fire so that it warms up, but does not catch fire! You will see how, as it heats up, a drawing or an inscription will begin to appear on a clean sheet of paper - what you drew with a pen.

To turn the invisible into the visible, it is not necessary to buy any special substances. Instead of ink, you can use some products that are quite likely to be found in the refrigerator or kitchen cabinet. Let's say milk. Or lemon juice. Or juice squeezed from onions. Or at least table vinegar. But in all cases, in order to develop an inscription or a picture, it is necessary to heat a piece of paper over a tile or a candle, making sure - I remind you again - that it is far enough from the tile or from the flame.

Author: Olgin O.M.

 We recommend interesting experiments in physics:

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