Dear students, you must like chemistry very much, so you can do an interesting little experiment by yourself. The theme of this experiment is dancing with small charcoal. Take a test tube, fill it with 3-4g solid potassium nitrate, then fix it upright on an iron frame with an iron clip, and heat the test tube with an alcohol lamp. When the solid potassium nitrate gradually melts, take a piece of charcoal the size of a small bean, put it in a test tube and continue to heat it. After a while, you will see the small carbon block suddenly jumping up and down on the liquid level in the test tube, and then turn it over by itself, like dancing, giving off a fiery red light, which is very interesting. Please enjoy the beautiful dance of Little Charcoal. Can you answer why Xiao Tan dances?

answer

It turned out that when the small charcoal was just put into the test tube, the temperature of potassium nitrate in the test tube was low, so the small charcoal was still lying there. After heating the test tube, the temperature rises to make the small charcoal reach the ignition point. At this time, there is a fierce chemical reaction with potassium nitrate, which releases a lot of heat and makes the small charcoal burn and glow immediately. Because potassium nitrate decomposes at high temperature to release oxygen, this oxygen immediately reacts with small charcoal to generate carbon dioxide gas, which pushes small charcoal up at once. After the charcoal jumped up, it was out of contact with the potassium nitrate liquid below, the reaction was interrupted, and carbon dioxide gas was no longer produced. When the small charcoal falls back to potassium nitrate due to gravity, it reacts again and jumps up for the second time. In this cycle, Xiao Tan will keep jumping up and down.

2. Sugar turns into "black snow"

White sugar is a substance that people often eat. It is small white particles or powder, like snow in winter. However, I can turn it into "black snow" right away. If you don't believe me, please take a look at the following experiment. Put about 5g of white sugar into a 200ml beaker, and then drop a few drops of heated concentrated sulfuric acid. Suddenly, the sugar turned into a pile of fluffy "black snow", and the volume of the "black snow" gradually increased, even overflowing the beaker. Sugar suddenly became

Black Snow, that's interesting. Who knows the secret here?

answer

It turns out that there is a chemical reaction between sugar and concentrated sulfuric acid called dehydration. Concentrated sulfuric acid has a particularly eccentric hobby, that is, it especially wants to combine with water. It makes full use of the moisture in the air, even the moisture in other substances. As soon as we meet, it will take the water away. Sugar is a kind of carbohydrate (C 12H22O 1 1). When it meets concentrated sulfuric acid, the water in the sugar molecules is immediately taken away by it, and the rest is the poor sugar with carbon, which turns black. Concentrated sulfuric acid is not satisfied with taking water for its own use. It uses another skill-oxidation, which oxidizes part of the residual carbon in white sugar to generate carbon dioxide gas to escape.

C+2H2SO4=2H2O+2SO2+CO2

Due to the escape of carbon dioxide and sulfur dioxide gas produced after the reaction, the volume is getting bigger and bigger, and finally it becomes fluffy "black snow". In the "battle" of concentrated sulfuric acid against water, it is an exothermic process, so it gives a sneer and provides heat for the process of continuous oxidation of carbon by concentrated sulfuric acid.

3, no light bulb

An interesting chemistry performance in a middle school is going on enthusiastically, and one of the programs is particularly eye-catching. I saw a 200-watt light bulb hanging on a wooden pole, giving off dazzling white light. As far as brightness is concerned, ordinary electric lights are far behind. However, this light bulb has no wires, because it is a light bulb without electricity. Please think about it, where is the secret of this light bulb without electricity?

answer

It turns out that this bulb is filled with magnesium bars and concentrated sulfuric acid, and they have a fierce chemical reaction in the bulb, producing exothermic light. As we all know, concentrated sulfuric acid has strong oxidation ability, especially when it comes to some metals. Magnesium metal is particularly easy to be oxidized, so they are naturally "a match made in heaven". As soon as they meet, they will have a chemical reaction immediately:

Magnesium +2h2so4 (concentrated) = = magnesium sulfate +SO2+2h2o

In the process of reaction, a lot of heat is released, which makes the temperature in the bulb rise sharply and makes the magnesium bar reach the ignition point quickly. Under the condition of sufficient oxygen supply from concentrated sulfuric acid, magnesium bars burn more violently, just like flares.

4, water purification expert-alum

Speaking of alum, people are familiar with it, and some people call it alum, and the chemical name is potassium aluminum sulfate. But alum is not only used as a chemical raw material, but also a water purification expert! Once we went to the countryside for investigation, and when we were cooking lunch, we found that the water in the tank was too muddy to use. Just as we were worried, technician Zhang from the agricultural technology station came. Seeing that there was nothing we could do, he immediately took out a few pieces of alum, ground it into fine powder and sprinkled it in the jar. After a while, the water in the tank became clear and transparent. Although it has been several years, it is still fresh in my memory. However, I still don't understand why. Please explain it to me.

answer

It turned out that the mud dust in the water was "caught" by alum and sank to the bottom of the pool together. So, why can alum "catch" the mud and dust in running water? This should start with the turbidity of water itself. Tiny dirt and dust in water are not easy to settle down because of their light weight, and they "swim" in the water, making the water turbid. In addition, these tiny particles have another feature, that is, they like to pull some ions in the water to their side, or ionize some ions themselves, thus turning themselves into charged particles, which are often negatively charged. Because like charges repel and opposite charges attract, these negatively charged particles repel each other and cannot get together, so there is no chance to form larger particles and settle down. Alum, on the other hand, has a strange ability to make these inaccessible particles run together. When alum meets water, there will be a hydrolysis reaction with potassium sulfate as the supporting role and aluminum sulfate as the protagonist. Aluminum sulfate reacts with water to form a white flocculent precipitate-aluminum hydroxide. The generated positively charged aluminum hydroxide "hugs" each other as soon as it comes into contact with negatively charged sludge and dust particles. In this way, many particles gather together, and the particles get bigger and bigger, and finally they all sink to the bottom of the water, and the water becomes clear and transparent.

Simply put, it is the hydrolysis of aluminum ions.

5. Boiled eggs with lime

The school building of Nanjing primary school is going to be repaired again, and the workers and teachers are arguing like boiling water. HuiQing and Yan Li stood watching curiously, chatting. Hui Qing said, "Look at this heat, you can definitely cook the eggs." Li Yan said: "Impossible." To find out, they took an egg from home and buried it in a pile of steaming lime. After a while, the egg exploded with a bang. They are even more puzzled when they see this situation. They thought about it and didn't understand what was going on. Who can explain it to them?

answer

There is a simple reason. The chemical name of quicklime is calcium oxide, which becomes hydrated lime after adding water, and the chemical name is calcium hydroxide, commonly known as white ash. The process of converting quicklime into hydrated lime is called "digestion", which is an exothermic reaction:

6. Unstable sanitary ball

Speaking of fitness balls, everyone must be familiar with them. They are often used to kill moths in suitcases. However, what happens when you put it in an aqueous solution containing acetic acid and baking soda? At first, it slept at the bottom of the cup. After a while, it became restless, but it jumped up and down in the water like crazy. Who knows why?

answer

After this chemical reaction, the easily generated carbon dioxide gas becomes tiny bubbles attached to the bottom or wall of the cup, and the whole body of the sanitary ball is covered by these bubbles. Carbon dioxide is lighter than water, so it will rise to the surface. Once the bubbles on the sanitary ball reach a certain level, they will rise straight like a drowning person pulling a lifebuoy. When the sanitary ball rises to the water surface, the small bubbles attached to the sanitary ball burst due to the decrease of pressure, and the sanitary ball recovered its original proportion and lost its "life buoy", so it sank back to the bottom of the cup, stuck enough small bubbles and floated up again. In this way, the sanitary ball will run around.

7. The origin of "bhc" powder name.

An insect pest occurred in a wheat field in the suburbs. In order to resist disasters and kill insects, farmers sprayed a chemical pesticide powder called "bhc". At this time, clever classmate A solemnly asked classmate B: "Why do you say this pesticide is called' BHC' powder?" "I don't know yet, because when this pesticide was invented, scientists experimented 666 times." Student B answered confidently. A classmate retorted, "What you said is wrong. It is said that this pesticide is made of 666 kinds of drugs, so it is called' BHC' powder. The two students are arguing with each other. ...

Please comment. Which of them is right? Why?

answer

Neither of the two students is right. This insecticide is produced by the reaction of a chemical called benzene with chlorine under ultraviolet radiation.

C6H6 13C 12 = C6H6Cl6

As can be seen from the molecular formula of the generated BHC powder, its molecule consists of six carbon atoms, six hydrogen atoms and six chlorine atoms, so it is called BHC powder.

8. The magical use of ammonium chloride fireproof cloth

Dear students, I soaked an ordinary cotton cloth in the saturated solution of ammonium chloride. After a while, I took it out to dry and made a fireproof cloth. This chemically treated cloth, if ignited with a match, will not ignite and will emit white smoke. Please tell me, what is the reason?

answer

It turns out that the surface of this chemically treated cotton cloth (fireproof cloth) is covered with crystal particles of ammonium chloride, which has a strange temper, that is, it is particularly afraid of heat. When heated, it will undergo chemical changes and decompose two kinds of non-combustible gases, one is ammonia and the other is hydrogen chloride.

NH4Cl-& gt； NH3 (gas) +HC 1 (gas)

These two gases isolate cotton cloth from air, and cotton cloth can't burn without oxygen. When these two gases protect cotton cloth from fire, they meet in the air and recombine into small crystals of ammonium chloride, which are scattered in the air like white smoke. In fact, ammonium chloride is a good expert in fire prevention. The stage scenery of the theater and the wood on the ship are often treated with ammonium chloride to achieve the purpose of fire prevention.

9. The ups and downs of eggs

Fill a big beaker with dilute hydrochloric acid solution, then put a fresh egg in the beaker, and it will immediately bottom out. After a while, the egg rises to the liquid level again, and then sinks to the bottom of the cup. After a while, the egg floats to the liquid level again, and so on many times. Please analyze it. What is the reason?

answer

Because the main component of egg shell is calcium carbonate, it will react with dilute hydrochloric acid to generate calcium chloride and carbon dioxide gas.

Cac0312hc1= CAC121c02 (gas) 1H20.

The bubbles formed by carbon dioxide gas are tightly attached to the eggshell, and the buoyancy generated makes the eggs float. When the egg rises to the liquid level, the pressure on the bubbles is less, some bubbles burst, and carbon dioxide gas diffuses into the air, thus reducing the buoyancy and the egg begins to sink again. When it sinks to the bottom of the cup, the dilute acid constantly reacts with the eggshell, constantly producing carbon dioxide bubbles, thus making the egg float again. In this way, the egg moves up and down repeatedly. Finally, when the eggshell comes into contact with hydrochloric acid, the reaction stops and the up-and-down movement of the egg stops. But at this time, because the liquid in the cup contains a lot of calcium chloride and residual hydrochloric acid, the specific gravity of the liquid is greater than that of the egg, so the egg finally floats on the liquid.

10, not "glass cutter" in glass cutter.

Dear students, do you want to carve a beautiful pattern on a piece of glass? You can use glass cutter's "glass cutter" to carve this pattern. The method is simple. Coat the glass with a thin layer of molten paraffin. After coagulation, use the needle tip to carve the pattern you need on the paraffin. In addition, take a lead evaporating dish, put calcium fluoride and sulfuric acid in the evaporating dish, put a circle of rubber on the edge of the evaporating dish, then put the waxed picture face down on the evaporating dish, heat it slightly, and wipe off the paraffin on the surface with gasoline. At this time, beautiful patterns were carved on the glass. You must find it interesting, so please think about it. This is not glass cutter's "glass cutter". What is it? Why can it carve patterns on glass?

answer

This glass cutter is not glass cutter, but hydrofluoric acid. Because calcium fluoride reacts with sulfuric acid to generate hydrogen fluoride and calcium sulfate, hydrogen fluoride gas volatilizes from the solution into the glass and dissolves in the water above the glass to form hydrofluoric acid, which does not react with paraffin, but has a very strange chemical temper, that is, it reacts with silicon dioxide, the main raw material for forming glass, and generates water and fluoride gas after the reaction. This kind of acid that can "eat" glass is not called "glass cutter" in glass cutter. In this way, any glass surface that is not covered and protected by paraffin (that is, the pattern part) is "eaten" by this acid, and the pattern on the glass appears after removing paraffin. The reaction is as follows:

4HF ten Si02 = 2H20 ten SiF4 (gas)

1 1. The glass rod ignited the ice.

Glass rods can ignite ice cubes. You must think this is a joke. However, what I said is completely true. It is surprising that ice can burn. What is even more surprising is that in the absence of matches and lighters, as long as a glass rod is gently used, the ice will burn immediately and will not go out for a long time. You can do an experiment if you are interested. First, pour 1-2 small potassium permanganate into a small dish, gently grind it into powder, then drop a few drops of concentrated sulfuric acid and stir it evenly with a glass rod. The glass rod immersed in this mixture is an invisible small torch, which can ignite alcohol lamps or ice cubes. However, put a small piece of calcium carbide on the ice in advance, so that the ice will burn as long as it is gently touched with a glass rod. Please answer after the experiment.

answer

There is a simple reason. Calcium carbide (chemically called calcium carbide) on the ice surface reacts with a small amount of water on the ice surface, and the calcium carbide gas (chemically called acetylene) produced by this reaction is flammable. Because concentrated sulfuric acid and potassium permanganate are both strong oxidants, they are enough to oxidize calcium carbide gas, reach the ignition point immediately, and make calcium carbide gas burn. In addition, because the reaction between water and calcium carbide is exothermic, the combustion of calcium carbide gas is exothermic, and more and more water is melted into ice cubes, so the calcium carbide reaction is more and more rapid, and the calcium carbide gas is more and more, and the fire is more and more prosperous.

12, learn about copper in silver

High purity silver wire is needed in the production process of the factory. One day, the supplier bought a batch of silver wires from other places. A technician looked at the silver wire and said, "This silver wire is impure and doped with copper, so it can't be used." But some people disagree with him that there is no copper in it. Who is right about these two statements? Please help readers to identify it by chemical methods to see if there is copper in this batch of silver wires.

answer

First, take a small amount of silver wire and dissolve it in concentrated nitric acid. Then take this small amount of solution and add it to the excess hydrochloric acid. If white precipitate is generated at this time, filter out the white precipitate. Then a large amount of ammonia water is added to the filtrate. If dark blue cuprammonia complex ions are generated, the existence of copper is proved. On the other hand, if there is no dark blue copper-ammonia complex ion, it is proved that there is no copper.

13, mysterious picture

In an interesting chemical performance, the performer performed a mysterious picture. He hung a piece of white paper on the wall, then picked up the sprayer and sprayed a colorless and transparent liquid on this piece of white paper. In a blink of an eye, a beautiful picture was presented to the audience. In the dark blue waves, there is a big red-brown ship. His performance surprised the audience! Obviously it is a blank sheet of paper, why did you suddenly spray a beautiful picture? Dear readers, do you know the secret of this performer's painting?

answer

This is an ordinary chemical reaction. The white paper hanging on the wall has been pretreated by the performers. On this piece of white paper, he first drew a surging sea with yellowish potassium ferrocyanide solution, and then drew a huge ship in the sea with colorless and transparent potassium thiocyanate solution. After drying, there is no trace on the white paper. It turns out that the sprayer is filled with ferric chloride solution. When ferric chloride solution is sprayed on white paper, two chemical reactions occur on white paper at the same time. One is that ferric trichloride reacts with potassium ferrocyanide to generate iron ferrocyanide (blue), and the other is that ferric trichloride reacts with potassium thiocyanate to generate iron thiocyanate (red-brown). In this way, the blue sea and the red-brown boat were "sprayed".