Magic Toothpick
Thinking: Will a toothpick placed in water swim with the sugar cubes placed in the water, or with the soap placed in the water? ?
Materials: toothpicks, a basin of water, soap, sugar cubes
Operation:
1. Place the toothpick carefully on the water.
2. Put the sugar cube into the water basin far away from the toothpick. The toothpick will move towards the sugar cube.
3. Change a basin of water, carefully place the toothpick on the water, and now put the soap in the basin closer to the toothpick. The toothpick will stay away from the soap.
Explanation:
When you put the sugar cube into the center of the basin, the sugar cube will absorb some water, so a small amount of water will flow in the direction of the sugar cube. The toothpick also moves with the water flow. However, when you put the soap into the basin, the surface tension on the edge of the basin is stronger, so it will pull the toothpick outward.
Creation: Please try to see which direction the toothpick will swim if you replace sugar and soap with other substances
Piece of paper with holes to hold water
Thinking: Why can paper with holes hold water?
Materials: a bottle, a pin, a piece of paper, a full cup of colored water
Operation:
p>1. Fill the empty bottle with colored water.
2. Poke many holes in the white paper with a pin.
3. Cover the mouth of the bottle with the perforated paper.
4. Press the paper with your hand and turn the bottle upside down so that the bottle mouth faces down.
5. Gently remove your hand. The paper covers the mouth of the bottle without moving, and the water does not flow out of the hole.
Explanation:
The thin paper can hold up the water in the bottle because the atmospheric pressure acts on the paper, creating an upward force. Small holes will not leak water because water has surface tension, and water forms a thin film on the surface of the paper, preventing water from leaking out. This is like an umbrella made of cloth. Although the cloth has many small holes, it still does not leak.
The secret of the handkerchief
Thinking: Spread the handkerchief flat under the faucet, turn on the faucet, will the water flow down through the handkerchief?
Materials: 1 glass, 1 handkerchief, 1 rubber band
Process:
1. Cover the mouth of the cup with a handkerchief and use a rubber band Tie tight.
2. Let the water wash on the handkerchief.
3. Turn off the faucet after the water flows into the cup until it is about seven to eight minutes full.
4. With the mouth of the cup facing down, quickly turn the cup over.
Instructions:
1. When flushing water from the cup, the water will flow into the cup through the handkerchief.
2. When the cup is turned upside down, the water will not flow out due to atmospheric pressure.
Extension:
If the cloth covering the mouth of the cup is different (such as cotton, towel, linen), what will happen to the water in and out?
1. Do measurement experiments and experience life
After learning to use a balance to measure the mass of an object, first estimate the mass of an egg, and then use a balance to measure it to see if your estimate is accurate. Then use a scale to weigh 10 eggs. Calculate the average mass of each egg and compare it with your estimate.
2． Do the inertia experiment with no risk
Put a piece of cardboard on the rim of a glass filled with half a glass of water, then put an egg on the piece of paper, pop the cardboard out with your hands, and the egg Will fall safely into the glass.
3. Do an inertia experiment and make an accurate judgment
Use one raw and cooked egg each, place them on the table, and rotate at the same speed at the same time. Because the yolk and egg white of the cooked egg are fixed, they rotate smoothly, while the raw egg Due to inertia, it shakes unsteadily and stops rotating quickly, so that raw eggs and cooked eggs can be accurately judged.
4. Doing pressure experiments is intuitive and clear
Pinch an egg with your hands. Since the force on the surface of the egg is uniform and the pressure is small, the egg is difficult to break. However, if we pinch two eggs with the same hand, Since the contact area between eggs is small and the pressure is strong, it is easy to crush the eggs.
5． Do atmospheric pressure experiments, which is full of fun
Place sand on the bottom of a wide-mouthed bottle that is slightly smaller than an egg, ignite the cotton soaked in alcohol and quickly put it into the bottle. It will be peeled later. The cooked egg blocks the mouth of the bottle. After a while, due to the strong atmospheric pressure, the cooked egg will be swallowed by the glass bottle.
6． Do a lively and interesting buoyancy experiment
Put a raw egg into a glass filled with water. You can see the egg sinking into the water. Then gradually add salt to the cup and stir continuously. You can see the eggs suspended anywhere in the water. Continue adding salt to the cup until the eggs float in the water. From this we can see the three states of eggs in salt water.
Biological experiment:
How to prepare plant leaf vein specimens
1. Experiment purpose:
1. Learn to make leaf vein specimens
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2. Cultivate hands-on skills and interest in biology classes
2. Drugs:
NaOH (strongly corrosive, special care should be taken when using), Na2CO3, Hydrogen peroxide (or bleaching powder), dye.
3. Equipment:
Beaker, electric stove, large tweezers, toothbrush, plastic plate, glass rod, small plastic bucket, absorbent paper (or straw paper)
4. Operation steps:
1. Material selection: Select leaves (such as osmanthus leaves, bodhi leaves) with thick leaves, moderate size, flat leaf surface and rich veins, wash them with clean water and set aside.
2. Prepare the solution: Weigh 35gNaOH and 25gNa2CO3 into a beaker, add 1L of water to dissolve, and make a solution.
3. Heating: Heat the solution in an electric furnace. When it is almost boiling, immerse the leaves into the solution. At this time, lower the temperature of the electric furnace and stir while heating; the length of 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, use tweezers to take out the leaves, put them into a small plastic bucket filled with water and rinse them clean (usually more than twice)
5. Brushing: Place the leaves in a plastic plate, add a layer of water, tilt the toothbrush (approximately 45 degrees to the horizontal), and gently brush the flesh along the veins of the leaves. When brushing, be careful: only brush in one direction (absolutely not back and forth) ) to avoid damaging the leaf veins. When brushing, start from the back side first, brush the back side and then the front side. You can use the tapping method on the edge of the main leaf veins. Brush clean and place on absorbent paper (or straw paper) to dry.
6. Bleaching: Use 20% hydrogen peroxide (or bleaching powder) to bleach the leaf veins.
7. Dyeing and drawing: You can use red liquid, violet liquid, magenta and dyes to dye the leaf veins, or draw on the leaf veins.
8. Paste and glue: After drying, you can stick it with paper and glue it for storage.
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The magical power of chopsticks
Thinking: Insert a chopstick into a cup filled with rice, and then lift the chopstick up. The chopstick will melt the rice. Mention the cup?
Materials: One plastic cup, one cup of rice, one bamboo chopstick
Operation:
1. Fill the plastic cup with rice.
2. Press the rice in the cup with your hands.
3. Hold the rice with your hand and insert the chopsticks between your fingers.
4. Gently lift the chopsticks with your hands, and the cup and rice will be lifted together.
Explanation:
Due to the squeezing between the rice grains in the cup, the air in the cup is squeezed out. The pressure outside the cup is greater than the pressure inside the cup, causing the chopsticks and the rice grains to cleave together. The two are tightly joined together, so the chopsticks can lift the rice cup.
Bottle Race
Thinking: Two bottles of equal weight containing sand and water roll down from a height. Who reaches the finish line first?
Materials: two bottles of the same size and weight, sand, water, a rectangular board, two thick books
Operation:
1. Use The rectangular wooden board and the two books form a slope
2. Pour the water into another bottle and pour the sand into the bottle
3. Place the two bottles on the wooden board , let the two bottles roll down at the same starting height at the same time
4. The bottle filled with water reaches the end point earlier than the bottle filled with sand
Explanation:
The friction of sand against the inner wall of the bottle is much greater than the friction of water against the inner wall of the bottle, and there is also friction between the sand, so it slides slower than the bottle filled with water.
Creation: Change the substances in the bottles and let them compete!
Electric newspapers
Thinking: Without glue, tape or other adhesives, newspapers can be stuck on the wall without falling off. Do you know why?
Materials: 1 pencil; 1 newspaper.
Steps:
1. Unfold the newspaper and lay it flat on the wall.
2. After quickly rubbing the side of the pencil on the newspaper a few times, the newspaper will not fall off as if it is stuck to the wall.
3. Lift up a corner of the newspaper and then let go. The lifted corner will be sucked back by the wall.
4. Slowly peel the newspaper off the wall and listen for the sound of static electricity.
Instructions:
1. Rub the pencil to charge the newspaper.
2. The charged newspaper was sucked to the wall.
3. When the air in the house is dry (especially in the winter), if you peel the newspaper off the wall, you will hear a static crackling sound.
Creation: Please give it a try, what other items can be stuck on the wall using static electricity without using adhesives
Separation of pepper and salt
Thinking: I accidentally mixed the kitchen seasonings: pepper and salt together. How to separate them?
Materials: pepper, salt, plastic spoon, small plate
Operation:
1. Mix salt and pepper together.
2. Stir evenly with chopsticks.
3. Rub the plastic spoon on the clothes and place it on top of the salt and pepper.
4. The pepper sticks to the spoon first.
5. Move the plastic spoon downward slightly.
6. The salt sticks to the spoon.
Explanation:
The reason why pepper is electrostatically adsorbed earlier than salt is because its weight is lighter than salt.
Create:
Can you use this method to separate other mixed ingredients?
Electric Balloons
Thinking: Under what circumstances will two balloons attract each other, and under what circumstances will they repel each other?
Materials: Inflated Balloons 2 , 1 piece of string, 1 piece of cardboard
Operation:
1 Inflate the two balloons separately and tie a knot at the mouth.
2 Connect the two balloons with string.
3 Rub the balloon on your hair (or sweater).
4 Lift the middle part of the string and the two balloons immediately separate.
5 Place cardboard between two balloons and the electricity on the balloons causes them to be attracted to the cardboard.
Explanation:
1 The electricity on one balloon repels the electricity on the other balloon.
2 The electricity on the two balloons causes them to be attracted to the cardboard.
Creation: Can you use other small experiments to show that the balloon is charged?
Cute watermark
Thinking: How are the beautiful patterns on rice paper made if they are not drawn?
Materials: 1 washbasin, 1-2 sheets of rice paper, 1 chopstick, 1 cotton swab, 1 bottle of ink, water (about half a basin)
Operation:
p>1. Pour half a basin of water into the basin and gently touch the water with chopsticks dipped in ink. You will see the ink expand into a circle on the water.
2. Take a cotton swab and rub it on the scalp two or three times.
3. Then tap the center of the ink circular pattern and see what happens.
4. Gently cover the calligraphy paper on the water, and then slowly pick it up. What pattern is printed on the paper?
Explanation:
1. When the cotton swab is touched, the ink will expand into an irregular circle shape.
2. The small amount of oil applied when the cotton swab is rubbed on the scalp will affect the force of water molecules pulling each other.
3. The watermark will appear in irregular concentric circles.
Create:
Try other ways to change the shape of the ink on the water.
Can you light the alcohol lamp with a glass rod instead of a match?
Experiment: Put a small amount of potassium permanganate crystals on a watch glass (or glass piece), drop 2 or 3 drops of concentrated sulfuric acid on the potassium permanganate, dip it with a glass rod, and then touch it The wick of the alcohol lamp was lit immediately.
Drip water ignites fire
Water can put out fires, but can it also start fires?
Experiment: Mix 5 grams of dry sucrose powder and 5 grams of potassium chlorate powder on an asbestos mesh, stir evenly with a glass rod, pile it into a hill, add 3 grams of sodium peroxide, drip with water, and wait for half a minute. White smoke erupted from the hillock, which soon caught fire.
The handkerchief that is indestructible
The handkerchief that has been burned by fire is actually intact?
Experiment: Soak a cotton handkerchief in a 1:1 solution of alcohol and water, then squeeze it gently, use two crucible tongs to clamp the two corners of the handkerchief, and put it on the fire to light. , when the flame decreases, shake the handkerchief quickly to extinguish the flame. You will find that the handkerchief is still intact.
Principle: When burning, the flame of alcohol is outside the water layer, and the water adsorbed in the fiber gaps absorbs the heat of combustion and evaporates. The temperature on the handkerchief does not reach the ignition point of the fiber, so the handkerchief does not burn.
Snowball burning
Can snowballs burn?
Of course, what burns is not the real snowball, but the calcium acetate precipitated by putting the calcium acetate solution in alcohol, just like white snow, made into a ball shape, and burns when ignited.
Experiment: Add 7 grams of calcium acetate to 20 ml of water to make a saturated calcium acetate solution, add it to 100 ml of 95 alcohol, stir while adding, and a solid like snow will precipitate.
Smoke from an empty cup
White smoke from an empty cup?
Experiment: Two clean and dry glasses, drop a few drops of concentrated hydrochloric acid into one, and drop a few drops of concentrated ammonia into the other. Rotate the glass until the droplets wet the wall of the glass, and then cover it with a glass piece. On the table, place the cup of concentrated hydrochloric acid upside down on the cup of concentrated ammonia, remove the glass piece, and gradually you will be able to see the cup full of white smoke.
1. Little Charcoal Dancing
Dear students, you must like chemistry very much, so you can do an interesting little experiment by yourself. The title of this experiment is called Little Charcoal Dance. Take a test tube, put 3 to 4 grams of solid potassium nitrate in it, fix it upright on the iron frame with an iron clamp, 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 into the test tube, and continue heating.
After a while, you will see small charcoal blocks suddenly jumping on the liquid surface in the test tube. Sometimes they jump up and down, and sometimes they turn over on their own, as if dancing, and emit a hot red light. It is very interesting. Please enjoy Xiao Zatan's beautiful dance. Can you answer why Little Charcoal dances?
Answer
It turns out that when the charcoal was first put into the test tube, the temperature of the potassium nitrate in the test tube was too low to cause the charcoal to burn, so the charcoal was still there. Lying down. After the test tube continues to be heated, the temperature rises, causing the charcoal to reach the ignition point. At this time, a violent chemical reaction occurs with potassium nitrate, and a large amount of heat is released, causing the charcoal to burn and glow immediately. Because potassium nitrate decomposes at high temperatures and releases oxygen, this oxygen immediately reacts with the small charcoal to form carbon dioxide gas, and this gas immediately pushes up the small charcoal. After the charcoal jumps up, it breaks out of contact with the potassium nitrate liquid below, the reaction is interrupted, and the carbon dioxide gas no longer occurs. When the small charcoal falls back to the potassium nitrate due to the effect of gravity, the reaction occurs again, and the small charcoal reacts again. Jump up a second time. This cycle goes back and forth, and the little charcoal keeps jumping up and down.
2. White sugar turns into "black snow"
White sugar is a substance that everyone often eats. It is in the form of small white particles or powder, like white snow in winter. However, I was able to turn it into "black snow" instantly. If you don’t believe it, please take a look at the experiment below. Put about 5 grams of white sugar into a 200 ml beaker, and then add a few drops of heated concentrated sulfuric acid. Suddenly the white sugar turns into a pile of fluffy "black snow", and with the sound of heat and steam, " The volume of "black snow" gradually increased, even filling the beaker. The white sugar suddenly turned into
'black snow.' It's really interesting. Who knows what the secret is here?
Answer
It turns out that white sugar and concentrated sulfuric acid occur Concentrated sulfuric acid has a particularly weird hobby, that is, it has a very strong desire to combine with water. It makes full use of the moisture in the air and does not let go of the moisture in other substances. As soon as it meets, it must snatch away the water. White sugar is a carbohydrate (C12H22O11). When it encounters concentrated sulfuric acid, the water in the sugar molecule is immediately taken away, leaving the poor white sugar with charcoal. After the concentrated sulfuric acid took the water for itself, it was not satisfied. It used another skill - oxidation. It oxidized part of the remaining carbon in the sugar, generating carbon dioxide gas and running out. .
C 2H2SO4=2H2O 2SO2 CO2
As the carbon dioxide and sulfur dioxide gas generated after the reaction escape, the volume becomes larger and larger, and finally turns into fluffy "black snow" ". In the "battle" of concentrated sulfuric acid to capture water, it is an exothermic process, so it makes a chirping sound and provides heat for the concentrated sulfuric acid to continue the process of oxidizing carbon.
3. No electricity Light bulb
An interesting chemistry performance in a middle school is in full swing. One of the shows is particularly eye-catching. There is a light bulb of about 200 watts hanging on a wooden pole. This light bulb emits a dazzling light. White light, in terms of brightness, is beyond comparison with ordinary electric lamps. However, this light bulb does not have any wires, because it is a light bulb that does not use electricity. Please think about it. Where is the secret?
The answer
It turns out that this light bulb contains magnesium strips and concentrated sulfuric acid, which undergo a violent chemical reaction inside the bulb, causing exothermic light. Concentrated sulfuric acid has strong oxidizing properties, especially when it meets some metals. Magnesium metal is a substance that is particularly easy to be oxidized, so the two are naturally "matched" as long as they meet. , a chemical reaction of desorption occurs immediately:
Mg+2H2SO4 (concentrated) = MgSO4+ SO2+2H20
A large amount of heat is released during the reaction, causing the temperature inside the light bulb to rise sharply, quickly When the magnesium strip reaches the ignition point, and the concentrated sulfuric acid is fully supplied with oxygen, the magnesium strip burns more vigorously, just like a flare.
4. Water purification expert - alum
Speaking of alum, people are very familiar with it. Some people call it alum, and its chemical name is potassium aluminum sulfate. However, alum is not only used as a chemical raw material, it is also an expert in water purification! Once, we went to the countryside to conduct research. While making lunch, we found that the water in the tank was too muddy to be used. When we were worried about this, technician Zhang from the Agricultural Technology Station came. He saw that we had no solution. Immediately take out a few pieces of alum, grind it into fine pieces, and then sprinkle it in the water tank. After a while, the water in the tank became crystal clear. Although this incident happened several years ago, it is still fresh in my memory. However, I still don’t understand what it means. Please explain it to me.
Answer
It turns out that after the mud dust in the water was "caught" by alum, it sank to the bottom of the tank together. So, why can alum "catch" mud dust in water? This has to start with the turbidity of the water itself. The extremely small mud and dust in the water are not easy to settle due to their light weight, and they "wander" in the water, making the water turbid. In addition, these tiny particles also have a characteristic, that is, they like to pull certain ions from the water to themselves, or ionize some ions themselves, thereby turning themselves into charged particles. These charged particles Particles tend to have a negative charge. Because charges of the same sex repel and charges of opposite sex attract, these negatively charged particles repel each other and cannot come together. They have no chance to form larger particles and precipitate. Alum has the unique ability to make these particles that cannot get close to each other run together. , as soon as alum meets water, a hydrolysis reaction occurs. In this reaction, potassium sulfate is a supporting role and aluminum sulfate is the protagonist. The reaction between aluminum sulfate and water produces a white flocculent precipitate - aluminum hydroxide. The generated aluminum hydroxide with a positive charge "hugs" each other as soon as it encounters the negatively charged dust particles. In this way, many particles gather together, and the particles become larger and larger. Finally, they both sink to the bottom of the water, and the water becomes clear and transparent.
To put it simply, it is the hydrolysis of aluminum ions
5. Boiled eggs with lime
The school building of Nanjing Primary School needs to be renovated. Like boiling a pot. Two classmates, Huiqing and Yanli, stood aside and watched curiously while discussing. Huiqing said: "Looking at the heat, the egg can be cooked." Yanli said: "It's impossible." In order to find out, they took an egg from home and buried it in the steaming lime pile. After a while, I heard a "pop" sound and the egg exploded. Seeing this situation, they became even more puzzled. They couldn't figure out what was going on after much thought. Who could explain it to them?
Answer
The reason is simple. The chemical name of quicklime is calcium oxide. After adding water, it becomes slaked lime. The chemical name is calcium hydroxide, which is commonly known as white ash. The process of turning quick lime into slaked lime is called "digestion", which is an exothermic reaction:
6. Unstable sanitary balls
Speaking of sanitary balls, everyone must be familiar with them. Use it to kill borers in your trunks. However, what happens when you put it into a water solution containing acetic acid and baking soda? At first, it kept sleeping at the bottom of the cup, but after a while, it stopped being quiet and jumped up and down in the water, as if it was suffering from madness. Does anyone know why this is?
Answer
The carbon dioxide gas easily generated through this chemical reaction turns into very small bubbles that stick to the bottom or wall of the cup. Sanitary balls My whole body is covered with these little bubbles. Carbon dioxide is lighter than water and will rise to the surface of the water. Once the bubbles stuck to the sanitary ball reach a certain level, it will rise straight up like a drowning person pulling on a lifebuoy. When the sanitary ball rose to the water surface, due to the reduction in pressure, the small bubbles attached to the sanitary ball burst. The sanitary ball returned to its original specific gravity and lost its "lifebuoy", so it sank back to the bottom of the cup again. When enough small bubbles are attached, they float up again. This cycle goes back and forth, and the sanitary ball keeps running.
7. The origin of the name "666" powder
An insect infestation occurred in a wheat field on the outskirts of the city. In order to fight against the disaster, farmers sprayed a powder called "666" of chemical pesticides. At this time, classmate A, who loves to use his brain, asked classmate B seriously: "Tell me, why is this pesticide called '666' powder?" "I don't know yet, because when this pesticide was invented, scientists We have experimented six hundred and sixty-six times." Student B answered confidently. Classmate A retorted: "You are wrong. I heard others say that this pesticide is made from 666 kinds of medicines, so it is called '666' powder." The debate continues...
Readers are asked to comment, which one of them is right?
Answer
Neither of the two students is right? . This pesticide is produced by reacting a chemical called benzene with chlorine under ultraviolet irradiation.
C6H6+3C12=C6H6Cl6
"It can be seen from the molecular formula of the powder: Its molecule is composed of six carbon atoms, six hydrogen atoms, and six chlorine atoms, so it is called "666duo, powder."
8. The wonderful use of ammonium chloride - fireproof cloth
Dear classmates, I soaked a piece of ordinary cotton cloth in a saturated solution of ammonium chloride. After a while, I took it out to dry. Thousands of them become fireproof cloth. When the chemically treated cloth was lit with a match, it not only failed to light, but also emitted white smoke. Please tell me, what does this mean?
Answer
It turns out that the surface of the chemically treated cotton cloth (fireproof cloth) is covered with crystal particles of ammonium chloride. Ammonium chloride, a chemical substance, has He has a weird temper and is particularly afraid of heat. When exposed to heat, he will undergo chemical changes and decompose into two incombustible gases, one is ammonia and the other is hydrogen chloride gas.
NH4Cl—gt; NH3 (gas) + HC1 (gas)
These two gases isolate the cotton cloth from the air. Of course, the cotton cloth cannot burn without oxygen. While these two gases protect the cotton from being burned by fire, they meet again in the air and recombine to form small crystals of ammonium chloride. These small crystals are distributed in the air like white smoke. In fact, the chemical substance ammonium chloride is a very good fire prevention expert. The stage scenery in the theater and the wood on the ship are often treated with ammonium chloride in order to achieve the purpose of fire prevention.
9. The sinking and floating of an egg
Put dilute hydrochloric acid solution into a large beaker, and then put a fresh egg into the beaker, it will bottom immediately. After a while, the egg rises to the liquid surface again, and then sinks to the bottom of the cup. After a while, the egg floats to the liquid surface again, and this can be repeated many times. Please analyze, what is the truth of this?
Answer
Since the main component of egg shell is calcium carbonate, a chemical reaction will occur when encountering dilute hydrochloric acid to generate calcium chloride and carbon dioxide gas.
CaC03 + 2HC1 = CaC12 + C02 (gas) + H20
The bubbles formed by carbon dioxide gas are tightly attached to the eggshell, and the buoyancy generated makes the egg rise. When the egg When it rises to the liquid surface, the pressure on the bubbles is small, some of the bubbles burst, and the carbon dioxide gas diffuses into the air, thereby reducing the buoyancy and the egg begins to sink again. As it sinks to the bottom of the cup, the dilute acid continues to react chemically with the eggshell and continuously generates carbon dioxide bubbles, causing the egg to float again. This cycle moves up and down. Finally, when the egg shell is completely destroyed by the hydrochloric acid, the reaction stops and the egg's up and down movement stops. But at this time, because the liquid in the cup contains a large amount of calcium chloride and remaining hydrochloric acid, the final specific gravity of the liquid is greater than the specific gravity of the egg. Therefore, the egg finally floats on the top of the liquid.
10. A "glass knife" that is not a glass knife
Dear students, do you want to carve a beautiful pattern on a piece of glass? You can use a “glass knife” other than a glass knife to carve this pattern.
The method is very simple. Apply a thin layer of molten paraffin on the glass. After it condenses, use the tip of a needle to carve the pattern you need on the paraffin. In addition, take a lead evaporation dish, put calcium fluoride and sulfuric acid in the evaporation dish, place a ring of rubber on the edge of the evaporation dish, then place the wax-coated painting face down on the evaporation dish, heat it slightly, and use gasoline to Wipe off the paraffin on the surface. At this moment, beautiful patterns on the glass are carved out. You must find it interesting, so please think about it, what is this "glass knife" that is not a glass knife? Why can it carve patterns on glass?
Answer
This "glass knife" that is not a glass knife is hydrofluoric acid. Because calcium fluoride reacts with sulfuric acid to form hydrogen fluoride and calcium sulfate, the hydrogen fluoride gas evaporates from the solution to the glass and dissolves in the water on the glass to form hydrofluoric acid. Hydrofluoric acid does not react with paraffin, but it does It has a very peculiar chemical property, which specifically reacts with silica, the main raw material for forming glass, and produces water and fluoride gas after the reaction. This kind of acid that can "eat" glass is called not a glass knife. "Glass Knife". In this way, any glass surface that is not protected by paraffin (ie, the pattern part) is "eaten" by this acid. After the paraffin is removed, the pattern on the glass is displayed. The reaction is as follows:
4HF+Si02=2H2SiF4 (gas)
11. The glass rod ignites the ice cubes
The glass rod can ignite the ice cubes. You must have thought this was a joke. However, what I said is completely true. Ice cubes can burn, which will surprise people, and what is even more surprising is that without matches or lighters, just tap lightly with a glass rod, and the ice cubes will burn immediately and will not go out for a long time. If you are interested, you can do an experiment and see. First, pour 1 to 2 small grains of potassium permanganate in a small dish, grind it gently into powder, then add a few drops of concentrated sulfuric acid, stir evenly with a glass rod, dip the glass rod in this mixture , is an invisible small torch that can light alcohol lamps and ice cubes. However, put a small piece of calcium carbide on the ice cube in advance, so that as long as you lightly touch the ice cube with a glass rod, the ice cube will burn immediately. Readers are asked to give their answers after experimenting.
Answer
The reason is simple. The calcium carbide on the ice (the chemical name is calcium carbide) reacts with a small amount of water on the ice surface. The calcium carbide gas (the chemical name is acetylene) generated by this reaction is a flammable gas. Since concentrated sulfuric acid and potassium permanganate are both strong oxidants, they are enough to oxidize the calcium carbide gas and immediately reach the ignition point, causing the calcium carbide gas to burn. In addition, since the reaction between water and calcium carbide is an exothermic reaction, and the combustion of calcium carbide gas releases heat, The ice melts into more and more water, so the calcium carbide reaction becomes faster and more calcium carbide gas is produced, and the fire becomes more and more prosperous.
12. Identifying copper from silver
A certain factory requires high-purity silver wire during its production process. One day, the supply and salesman bought back a batch of silver wire from other places. A technician looked at the silver wire and said: "This silver wire is impure. It is mixed with copper and cannot be used." However, some people disagreed with his statement and thought that There is no copper in it. Who is right about these two statements? Please readers help them use chemical methods to identify whether 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 add this small amount of solution to excess hydrochloric acid. If a white precipitate forms, filter out the white precipitate. Then add a large amount of ammonia water to the filtrate. If dark blue copper ammonia ions are generated, it proves the presence of copper. On the contrary, if no dark blue copper ammonia ions are produced, it proves that there is no copper.
13. Mysterious Picture
At an interesting chemistry performance, the performer performed a mysterious picture. He hung a piece of white paper on the wall, then picked up a sprayer and sprayed a colorless and transparent liquid on the white paper. In a blink of an eye, a beautiful picture was displayed in front of the audience. A huge red-brown ship was sailing in the dark blue waves. His performance surprised the audience! It was obviously a blank piece of paper, but why did a beautiful picture appear in the blink of an eye?
Do you know, dear reader, what the secret is to the pictures this performer spews?
Answer
This is a common chemical reaction. The white paper hanging on the wall has been processed by the performer in advance. On this white paper, he first drew a turbulent sea with a light yellow potassium ferrocyanide solution, and then used a colorless The transparent potassium thiocyanide solution painted a giant ship in the sea. After drying, there was no trace on the white paper. It turns out that the sprayer is filled with ferric chloride solution. When the ferric chloride solution is sprayed on the white paper, two chemical reactions occur on the white paper at the same time. One is the reaction between ferric chloride and potassium ferrocyanide to produce ferric ferrocyanide (blue), the other is the reaction between ferric chloride and potassium thiocyanide to produce ferric thiocyanide (reddish brown). In this way, the blue sea and the red-brown giant ship "squirted" out.