Who has a simple and detailed scientific experiment material suitable for the fourth grade of primary school?

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 a basin away from 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.

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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 very strong, so the toothpick will be pulled 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 and turn the bottle upside down so that the bottle mouth is facing down.

Gently remove your hand, the paper will cover the bottle mouth and the water will not flow out of the hole.

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Tissue paper can hold up the water in the bottle, because atmospheric pressure acts on the paper, resulting in upward tension. Small holes will not leak water, because water has surface tension, water forms a water film on the surface of paper, and 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 water flow 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 flush 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.

When the cup is turned upside down, water will not flow out due to the 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 the mass of 10 eggs, calculate the average mass 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. When the cardboard is suddenly ejected by hand, 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, the boiled eggs will be swallowed by glass bottles due to atmospheric pressure.

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 add salt to the cup and keep stirring, and you can see that the eggs are suspended in any position in the water. Continue to add salt to 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 (strong corrosiveness, be careful when using), Na2CO3, hydrogen peroxide (or bleaching powder) and dye.

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. Solution preparation: 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 brushing, start from the back, brush the back and then brush the front, and knock out the main pulse. After brushing, put it on absorbent paper.

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.

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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 are closely combined with rice grains, so chopsticks can lift the cup with rice.

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.

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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: newspapers can be stuck on the wall without glue, tape and other things. 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 as if it were stuck on 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. The plastic spoon is rubbed on the clothes and put on the salt and pepper.

4. Pepper sticks to the spoon first.

5. Move the plastic spoon down a little.

6. Stick the spoon after salt.

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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 attracts them to the cardboard.

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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.

Rub a cotton swab on the scalp 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?

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1. When the cotton swab touches, the ink will swell into an irregular circle.

2. A small amount of oil on the scalp rubbed by cotton swabs will affect the strength of water molecules pulling each other.

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 tongs, light it on the fire, and shake the handkerchief quickly when the flame decreases, so as 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 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 precipitated from the calcium acetate solution in alcohol. Like snow, it 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: rotate two clean and dry glasses, one containing a few drops of concentrated hydrochloric acid and the other containing a few drops of concentrated ammonia water, so that the drops wet the glass wall and then cover it with a glass sheet. Invert the glass filled with concentrated hydrochloric acid on the glass filled with concentrated ammonia water, remove the glass piece, 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 topic of this experiment is small charcoal dance. Take a test tube and 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 and put it in a test tube. And heating is continued. After a while, you will see the small carbon block suddenly jump up and down on the liquid level in the test tube, and then turn it over by itself, giving off a glowing red light like dancing. 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, making the small charcoal reach the ignition point. At this time, it had a fierce chemical reaction with potassium nitrate, releasing a lot of heat, which made the small charcoal burn and glow immediately. Because potassium nitrate releases oxygen at high temperature, this oxygen immediately reacts with small charcoal to generate carbon dioxide gas. This gas lifted the small charcoal 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 the small charcoal jumps up for the second time. This cycle, small charcoal kept jumping up and down.

2. Sugar turns into "black snow"

White sugar is a substance that people often eat. Winter is small white particles or powdery snow. However, I can suddenly turn it into "black snow". If you don't believe me, please see 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, sugar turned into a pile of fluffy "black snow", which was still steaming before.

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

answer

There is a chemical reaction between white sugar and concentrated sulfuric acid called dehydration. Concentrated sulfuric acid has a particularly strange hobby, that is, it has a particularly strong desire to combine with water. It makes full use of the moisture in the air, even in other substances, and takes it away as soon as it meets. White sugar is a kind of carbohydrate (c12h22o1kloc-0/065438+), and the water in the sugar molecule is immediately taken away by it, leaving only carbon and turning black. Concentrated sulfuric acid is not satisfied when it takes water as its own. It uses another skill to oxidize. It oxidizes some carbon remaining in sugar and produces carbon dioxide gas.

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

Because the carbon dioxide and sulfur dioxide gas produced after the reaction are exhausted, 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 a sneer is issued, which provides heat for the 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 light bulb of about 200 watts hanging on a wooden pole. This kind of light bulb emits dazzling white light, which is beyond the reach of ordinary light bulbs in brightness. But this light bulb doesn't have any wires, because it is a light bulb without electricity. Please think about it. What's the secret of this light bulb being dead?

answer

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

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

During the reaction, a lot of heat is released, which makes the temperature in the bulb rise sharply and quickly makes the magnesium bar reach the ignition point. 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, everyone is familiar with it. 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 found that the water in the tank was too muddy to use when we were cooking lunch. Just as we were worried, technician Zhang from the agricultural technology station came. Seeing that we couldn't help it, he immediately took out a few pieces of alum, ground it into fine powder and scattered it in the jar. Soon, the water in the tank became clear and transparent. Although it has been many years, it is still fresh in my memory.

answer

It turned out that the dirt and dust in the water were "caught" by alum and sank to the bottom of the pool. So, why can alum "catch" the mud and dust in the water? This should start with the turbidity of water itself. Because of their light weight, tiny dirt and dust in the water are not easy to settle down and wander 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. These charged particles are usually negatively charged. Because like charges repel and opposite charges attract, these negatively charged particles repel each other and cannot get close to each other, so there is no chance to form larger particles and settle down. Alum has a strange ability to make these inaccessible particles run together. Alum will hydrolyze when it meets water, in which potassium sulfate is a supporting role. Aluminum sulfate is the main component. 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 soil 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, and the noise of the workers' masters is boiling. HuiQing and Li Yan stood watching curiously, talking. Hui Qing said, "Look at the heat, you can boil the eggs." Li Yan said: "Impossible." To find out, they took an egg from home and buried it in a steaming pile of lime. After a while, they only listened. "

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 health balls, everyone must be familiar with them. They are often used to kill moths in suitcases. However, what happens when you put them 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 jumped up and down in the water like crazy. Who knows why?

answer

The carbon dioxide gas easily produced by this chemical reaction 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 bubble attached to the sanitary ball reaches a certain level, it will rise straight like a drowning person pulling it to the lifebuoy. When the sanitary ball rises to the surface, the small bubbles attached to the sanitary ball are reduced by pressure. 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 again. Repeat this cycle, and the sanitary ball continues to run.

7. The origin of "bhc" powder name.

A wheat field in the suburbs is infested by insects. 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 think 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. Student A 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 bhc powder, its molecule is composed 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, and then took it out to dry, which became a fireproof cloth. When this chemically treated cloth was ignited with a match, it not only failed to ignite, but also emitted 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. Ammonium chloride is a chemical with a strange temper, but it is particularly afraid of heat. Chemical changes will occur when heated, and two kinds of non-combustible gases will be decomposed, 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. These two gases meet in the air while protecting cotton cloth from burning, 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. In order to achieve the purpose of fire prevention, the stage scenery of the theater and the wood on the ship are often treated with ammonium chloride.

9. The ups and downs of eggs

Put the dilute hydrochloric acid solution in a big beaker, and then put a fresh egg in the beaker, and it will immediately bottom out. After a while, the egg will rise to the surface again, then sink to the bottom of the cup, and then the egg will float to the surface 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 into the bottom of the cup, the dilute acid constantly reacts with the eggshell, constantly generating carbon dioxide bubbles, so that the egg floats again. Finally, when the shell of the egg is completely acted by 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. After solidification, you can carve the pattern you need on the wax with a needle tip. In addition, take a lead evaporating dish, put calcium fluoride and sulfuric acid in it, put an eraser on the edge of the evaporating dish, then put the waxed picture face down on the evaporating dish and heat it slightly, and you can use it. Why can it carve patterns on glass?

answer

This is not glass cutter's 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. Hydrofluoric acid does not react with paraffin, but it has a very peculiar chemical temper, that is, it reacts with silicon dioxide, the main raw material for forming glass, and after the reaction, it generates water and fluoride gas, which can "eat" the glass. People call it the "glass cutter" of non-glass cutter. In this way, any glass surface that is not covered and protected by paraffin (that is, the pattern part) will be "eaten" by this acid. After removing the paraffin, the pattern on the glass appears. Its reaction is as follows:

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

1 1. The glass rod ignited the ice.

You must think this is a joke. However, what I said is completely true. Ice can burn, which will surprise people. What is even more surprising is that the ice cubes will burn immediately without matches and lighters, and they will not go out for a long time. You can do an experiment if you are interested. First, pour 1 1 2 into a small dish. Then drop a few drops of concentrated sulfuric acid and stir evenly with a glass rod. The glass rod dipped in this mixture is an invisible small torch, which can ignite alcohol lamps and 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 test.

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 combustible gas. 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 releases heat and the ice melts.

12, learn about copper in silver

A factory needs high-purity silver wire in the production process. 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 don't agree 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, a small amount of silver wire is dissolved in concentrated nitric acid. Then, this small amount of solution is added to excess hydrochloric acid, and if a white precipitate is produced, it is filtered out. Then a large amount of ammonia water is added to the filtrate, and if dark blue copper-ammonia complex ions are generated, the existence of copper is proved. On the other hand, if there is no dark blue cuprammonia 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. A huge reddish-brown ship is sailing in the dark blue waves. His performance surprised the audience! This is a blank sheet of paper, but why did a beautiful picture suddenly appear? Dear readers, do you know the secret of this performer's pop-up picture?

answer

This is an ordinary chemical reaction. The white paper hanging on the wall has been treated by the performers in advance. He first drew a surging sea on this piece of white paper 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. The original sprayer contained 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".