Thinking: Will the toothpick in the water swim with the sugar cubes in the water or with the soap in the water?
Ingredients: toothpick, a basin of water, soap, sugar cube.
Operation:
1. Carefully put the toothpick on the water.
2. Put the sugar cubes in the basin, away from the toothpicks. The toothpick will move towards the sugar cube.
Change a basin of water, carefully put the toothpick on the water, and now put the soap in the basin near the toothpick. Toothpicks will stay away from soap.
Explanation:
When you put the cube in the center of the basin, it will absorb some water, so there will be a small water flow in the direction of the cube, and the toothpick will move with the water flow. However, when you put soap into the basin, the surface tension at the edge of the basin is strong, so you will pull the toothpick out.
Creation: Please try. If sugar and soap were replaced by other substances, which direction would the toothpick swim?
Perforated paper can hold water.
Thinking: Why can perforated paper block water?
Material: a bottle, a pin, a piece of paper, a full cup of colored water.
Operation:
1. Fill the empty bottle with colored water.
Punch many holes in the white paper with a pin.
3. Cover the bottle mouth with perforated paper.
4. Hold the paper with your hand, turn the bottle upside down, and make the bottle mouth face down.
Gently remove your hand, the paper will cover the bottle mouth and the water will not flow out of the hole.
Explanation:
A thin piece of paper can hold up the water in the bottle, because atmospheric pressure acts on the paper, producing upward tension. Water will not leak out from the small holes because water has surface tension, and water forms a water film on the surface of paper, so water will not leak out. This is like an umbrella made of cloth. Although this cloth has many holes, it still won't leak rain.
The secret of handkerchief
Thinking: Lay the handkerchief flat under the faucet and turn on the faucet. Does the water run down through the handkerchief?
Material: 1 glasses, 1 handkerchief, 1 rubber band.
Process:
1. Cover the cup with a handkerchief and tie it with a rubber band.
2. Let the water flow on the handkerchief.
3. Turn off the tap after the water flows into the cup for about seven or eight minutes.
4. Turn the cup upside down.
Description:
1. When flushing from the top of the cup, water will flow into the cup through the handkerchief.
2. When the cup is inverted, water will not flow out due to atmospheric pressure.
Extension:
If the cloth covering the handkerchief is different (such as cotton cloth or towel or linen), what will happen to the incoming and outgoing water?
1. Do measurement experiments and experience life.
After learning to measure the mass of an object with a balance, first estimate the mass of an egg, and then measure it with a balance to see if your estimation is accurate. Then use the balance to weigh 10 eggs, calculate the average weight of each egg, and compare it with your estimated value.
2. Doing inertia experiment is near misses.
Put a piece of cardboard on the glass mouth with half a glass of water, and then put an egg on the cardboard. Suddenly, the cardboard will be ejected by hand and the eggs will fall into the glass safely.
3. Do inertia experiments and make accurate judgments.
Put a raw egg and a cooked egg on the table respectively and rotate at the same speed. Because the yolk and albumen of cooked eggs are fixed, they rotate smoothly, while raw eggs stop rotating quickly because of inertia, so it can be accurately judged that raw eggs are cooked.
4. Do stress experiment, which is intuitive and clear.
Pinch an egg by hand, because the surface of the egg is evenly stressed and the pressure is small, it is difficult to crush the egg. However, if we pinch two eggs with the same hand, it is easy to crush the eggs because of the small contact area and high pressure between them.
Doing atmospheric pressure experiment is full of fun.
Spread a layer of sand on the bottom of the jar slightly smaller than the egg mouth, light the cotton soaked in alcohol and quickly put it into the jar. Later, the peeled cooked eggs will block the jar mouth. After a while, due to atmospheric pressure, boiled eggs will be swallowed by glass bottles.
6. Doing buoyancy experiments is lively and interesting.
Put a raw egg in a glass filled with clear water, and you can see the egg sink into the water. Then gradually put salt into the cup and keep stirring, and you can see that the eggs are suspended in any position in the water. Continue to put salt in the cup until the eggs float in the water. From this, we can see three States of eggs in salt water.
Biological experiment:
Method for making plant vein specimen
First, the purpose of the experiment:
1, learn to make venous specimens.
2. Biology class cultivates hands-on ability and interest.
Second, drugs:
NaOH (which is corrosive and should be used with special care), Na2CO3, hydrogen peroxide (or bleaching powder) and dyes.
Third, the equipment:
Beaker, electric stove, tweezers, toothbrush, plastic plate, glass rod, small plastic bucket, absorbent paper (or toilet paper)
Fourth, the operation steps:
1. Material selection: Choose leaves with thick, moderate size, flat leaves and rich veins (such as Osmanthus fragrans leaves and Bodhi leaves) and wash them with clear water for later use.
2. Preparation of solution: Weigh 35gNaOH and 25gNa2CO3 into a beaker, and add 1L water to dissolve to prepare a solution.
3. Heating: heat the solution with an electric furnace, and when the solution is close to boiling, immerse the blade into the solution. At this time, reduce the temperature of the electric furnace and stir while heating; The heating time depends on the leaves. After two or three minutes, you can take out a piece and observe it until the leaves turn brown (or the mesophyll falls off).
4. Rinse: Stop heating, take out the leaves with tweezers, and rinse them in a small plastic bucket filled with clear water (usually more than twice).
5. Brush: put the leaves in a plastic plate, add a layer of water, tilt the toothbrush (at an angle of about 45 degrees with the horizontal plane), and gently brush the minced meat along the veins. Pay attention when brushing: brush only in one direction (never brush back and forth) to avoid damaging the vein. When you brush, start from the back, and then brush the front after cleaning. Knock division can be used at the edge of the main pulse. After brushing, put it on absorbent paper (or toilet paper) to dry.
6. Bleaching: Bleaching the veins with 20% hydrogen peroxide (or bleaching powder).
7. Dyeing and painting: you can dye the pulse with mercuric chloride, purple syrup and magenta, or you can draw on the pulse.
8. Sticking and gluing: After drying, it can be pasted with paper and glued for preservation.
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The power of chopsticks
Thinking: Insert a chopstick into a cup filled with rice, and then lift the chopstick. Can chopsticks lift rice and cups?
Materials: a plastic cup, a rice cup and a bamboo chopstick.
Operation:
1. Fill the plastic cup with rice.
2. Press the rice in the cup by hand.
3. Hold the rice with your hands and put chopsticks between your fingers.
4. Gently lift chopsticks with your hands, and the cup and rice are lifted together.
Explanation:
Because of the extrusion between rice grains in the cup, the air in the cup is squeezed out, and the pressure outside the cup is greater than that inside the cup, so that chopsticks and rice grains are tightly combined and chopsticks can hold the rice cup.
Bottle race
Thinking: Two bottles of the same weight, one filled with sand and the other filled with water, roll down from a height. Who will reach the finish line first?
Materials: two bottles of the same size and weight, sand, water, a rectangular board and two thick books.
Operation:
1. Make a slope with a rectangular board and two books.
2. Pour water into another bottle and sand into the bottle.
3. Put two bottles on the board and let them roll down at the same starting height at the same time.
The bottle filled with water reaches the finish line earlier than the bottle filled with sand.
Explanation:
The friction between sand and the inner wall of the bottle is much greater than that of water, and there will be friction between sand, so its sliding speed is slower than that of a bottle filled with water.
Creation: change the substances in the bottle and let them compete!
Paid newspaper
Thinking: Without glue, tape and other things, newspapers can stick to the wall without falling off. Do you know why?
Material: 1 pencil; 1 newspaper.
Steps:
1. Spread the newspaper and lay it flat on the wall.
2. After a few quick rubs on the newspaper with one side of the pencil, the newspaper won't fall off just like sticking to the wall.
3. Lift a corner of the newspaper, and then let go, and the lifted corner will be sucked back by the wall.
Take the newspaper off the wall slowly and pay attention to the static sound.
Description:
1. Wipe the pencil to charge the newspaper.
2. The charged newspaper was sucked to the wall.
When the indoor air is dry (especially in winter), if you take down the newspaper from the wall, you will hear the crackle of static electricity.
Creation: Please have a try. What else can be stuck to the wall by static electricity without glue?
Separation of pepper and salt
Thinking: I accidentally mixed the kitchen condiments: pepper and salt. How can I separate them?
Ingredients: pepper, salt, plastic spoon, small dish.
Operation:
1. Mix salt and pepper.
2. Stir well with chopsticks.
3. Rub the plastic spoon on the clothes and put it on the salt and pepper.
4. Pepper sticks to the spoon first.
5. Move the plastic spoon down slightly.
6. After salt, stick it on the spoon.
Explanation:
Pepper is electrostatically adsorbed earlier than salt because its weight is lighter than salt.
Create:
Can you separate other mixed materials in this way?
Inflatable balloon
Thinking: When will two balloons attract each other and repel each other?
Material: 2 inflatable balloons, 1 string, 1 cardboard.
Operation:
1 Inflate two balloons separately and tie a knot in your mouth.
Connect two balloons with a thread.
Rub the balloon on your hair (or sweater).
Lift the middle part of the rope and the two balloons will separate immediately.
Put the cardboard between two balloons, and the electricity on the balloons makes them attracted to the cardboard.
Explanation:
The electricity on one balloon repels the electricity on the other balloon.
The electricity on the two balloons attracts them to the cardboard.
Creation: Can other small experiments be used to illustrate that balloons are charged?
Lovely watermark
Thinking: The beautiful patterns on rice paper are not drawn, but how are they made?
Materials: 1 washbasin, 1-2 rice paper, 1 chopsticks, 1 cotton swab, 1 bottle of ink and water (about half a basin).
Operation:
1. Pour half a basin of water into the washbasin and gently touch the water surface with chopsticks dipped in ink to see the ink on the water surface.
Expand into a circle.
2. Wipe the scalp with a cotton swab for two or three times.
3. Then touch the center of the ink circle and see what happens.
4. Gently cover the calligraphy paper on the water, and then pick it up slowly. What patterns are printed on the paper?
Explanation:
1. When the cotton swab touches, the ink will swell into an irregular circular pattern.
2. A small amount of oil on the scalp rubbed by cotton swabs will affect the mutual pulling force of water molecules.
3. The watermark will present irregular concentric circles.
Create:
Try other methods to change the ink pattern on the water surface.
Can a glass rod be used instead of a match to light an alcohol lamp?
Experiment: Put a small amount of potassium permanganate crystal on the mirror (or glass), drop 2 or 3 drops of concentrated sulfuric acid on potassium permanganate, dip it with a glass rod, and touch the wick of the alcohol lamp, and the alcohol lamp will light up immediately.
Drip ignition
Water can put out the fire, but can it be lit?
Experiment: Mix 5 grams of dry sucrose powder and 5 grams of potassium chlorate powder on an asbestos net, stir them evenly with a glass rod, pile them into hills, add 3 grams of sodium peroxide and drop them into water. Half a minute later, white smoke came out of the hill and soon burned.
An unbroken handkerchief.
The burnt handkerchief is actually intact?
Experiment: Soak the cotton handkerchief in the solution with the ratio of alcohol to water of 65,438+0: 65,438+0, then squeeze it gently, hold the two corners of the handkerchief with two crucible pliers, light it on the fire, and shake the handkerchief quickly to extinguish the flame when the flame decreases, and you will find that the handkerchief is still intact.
Principle: when burning, the flame of alcohol is outside the water layer, and the water absorbed in the fiber gap absorbs the heat of combustion and evaporates, so the temperature on the handkerchief can not reach the ignition point of the fiber, so the handkerchief can not be burned.
roll a snowball
Snowballs can burn?
Of course, it is not the real snowball that burns, but the calcium acetate separated from the calcium acetate solution in alcohol, like white snow, which is made into a ball and burned when it is ignited.
Experiment: Add 20 ml of water and 7 g of calcium acetate to make a saturated calcium acetate solution, add it to100 ml of 95% alcohol, and precipitate a snow-like solid under stirring.
An empty cup will smoke.
White smoke from an empty cup?
Experiment: Two clean and dry glasses, one with a few drops of concentrated hydrochloric acid and the other with a few drops of concentrated ammonia water, rotate the glasses to make the drops wet the glass wall, then cover the glass sheet, turn the glass with concentrated hydrochloric acid upside down on the glass with concentrated ammonia water, remove the glass sheet, and gradually you can see a glass full of white smoke.
1, small charcoal dance
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 "burst out".