MEL Chemistry
Hydrophobic sand DIY
updated
Equipment: glass bottle, rubber stopper with one hole, syringe.
Insert a syringe into a rubber stopper with one hole. Pour some hot water into a glass bottle, plug the neck with the stopper, and pull out the syringe plunger – the water boils!
As you pull the plunger on the syringe, the pressure inside the bottle decreases, and the boiling point of the water decreases with it. A similar phenomenon can be observed in the mountains: due to the increase in elevation, atmospheric pressure decreases, and with it, the boiling point of water. For example, on the summit of Everest, water boils at 69 °C (156.2 °F)!
Many more cool experiments are waiting for you in the MEL Physics subscription!
Warning! Only under adult supervision.
Equipment: paper cups, bamboo skewers, wooden popsicle sticks, rubber bands, zip ties, plastic lids, bead, hot glue, scissors, pliers, wire cutters, awl, stationery knife.
Race car: Poke 4 holes in a paper cup. Cut 2 small pieces and 1 large piece from a paper straw, pass them through the holes in the cup, and fix in place with hot glue. Trim the straws to even their lengths and insert bamboo skewers as axles.
Make and enlarge holes in four bottle caps. Put the “wheels” on the axles. Make a hole in the bottom of the cup and thread a rubber band through it, fixing it to the base of the cup with a paperclip and to the rear axle with a zip tie. Put one more rubber band on each rear wheel. Spin the wheels back to start the engine. Your car is ready!
Helicopter: Poke 4 holes opposite each other in the bottom of a paper cup. Attach 4 wooden skewers to the end of a paper straw and cut off the excess part of the straw. Insert the construction into the holes in the cup and fix in place with hot glue.
Make a hole in the middle of a wooden popsicle stick. Unbend a paperclip and pass it through the hole in the stick, bend the end back, and attach to the popsicle stick with hot glue. Add a bead to your makeshift propeller and put it in place. Fold a large rubber band on itself and pass a bamboo skewer through it. Break the skewer to fit in the base of the paper cup and hot glue it in place. Bend the propeller shaft and put the rubber band on the hook. Cut “blades” from a second paper cup and hot glue them to the propeller. Start the helicopter by rotating the blades counterclockwise. Your helicopter is ready to fly!
Boat: Poke two holes in a paper cup and thread a straw through them, fixing it with hot glue. Break a wooden popsicle stick into 4 equal pieces. Make 4 “tabs'' opposite each other in a plastic bottle cap and hot glue a popsicle stick piece to each one. Repeat once more to make a second propeller. Open the “hull” of the boat. Cut off the excess of the straw on both the inside and outside of the boat and thread a skewer through. Fix a plastic tie in the middle of the axis and trim the tail. Make a hole in each bottle cap and put them on the axis. Make a hole in the front of the boat and thread a cut rubber band through it, tie a knot in the rubber band, and trim the excess. Glue a stern to the boat to keep water out. Put a candle in a glass and pour boiling water over it to melt it: the paraffin should float to the surface. Use this paraffin to coat the boat. Start the engine by hooking the rubber band to the zip tie. Place some ballast in the front of the boat and launch it into the water.
All three mechanisms are based on the law of conservation of energy: as it stretches, a rubber band stores potential energy. The rubber band lengthens as it is wound around the axle and twists with itself; elastic force then returns the rubber band to its original length. Potential energy is converted into kinetic energy: the rubber band spins the helicopter’s propeller, boat’s motor, and car’s axle.
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Warning! Only under adult supervision.
Dry ice is solid carbon dioxide at a temperature lower than –78 °С (–108 °F). But the room’s temperature is about ~100 °С (~200 °F) higher! Under these conditions, the solid carbon dioxide rapidly becomes gaseous, which leads to the formation of gaseous layers under its solid pieces. This causes the solid pieces to remain on the water’s surface! Hovercrafts operate on a similar principle.
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Attention! All experiments are performed by professionals. Do not attempt.
Equipment: pencil, vegetable oil, Petri dish, mortar, glass.
Remove some graphite from a pencil and crush it to a fine powder in a mortar. Combine the resulting graphite powder with vegetable oil and stir – you’ve made a rheoscopic liquid! Such a fluid will allow you to visualize currents and trace its movement. Fill a glass to the brim with boiling water, set a Petri dish on the glass, and fill the Petri dish about halfway full with the mixture of oil and graphite. The water vapor heats the Petri dish and, after a while, cells will form on the surface of the oil mixture.
When the lower layers of the liquid become warmer than the ones above them, you’ll be able to observe flows as the warmer layer rises and the colder layer sinks.
These flows occur due to the fact that oil’s density decreases as it heats up. Under the influence of gravity, the less dense, warmer layer rises to the surface, and the denser, colder layer sinks. The layer that rises to the surface subsequently cools down, the descending layer heats up, and the movement continues. This phenomenon is called convection, and the currents caused by this process are called convection currents.
If you heat a rheoscopic fluid, you can see that convection can break into independent, closed Rayleigh-Benard cells under certain conditions. Mixing occurs independently in each cell, and there is practically no liquid transfer between them.
A similar experiment is included in the MEL Physics subscription!
Warning! Only under adult supervision.
A similar experiment is included in the MEL Chemistry subscription😉
To perform this and many other cool and safe experiments at home, sign up here: https://mel.sc/s2b/
Equipment: thick cardboard, foamiran, hot glue, clear tape, colorful paper, candy tray, scissors, pencil, ruler, small cylindrical glasses.
MEL Science Pop It: Make 2 frames from thick cardboard: cut out the same pattern of round holes in each one. Prepare a piece of foamiran for each hole. Glue them all to one of the frames and glue the second frame on top. Use a hairdryer to shape the bumps: heat each membrane and use an egg to mold it into the right shape. Your Pop It is ready! Try to craft a keychain this way!
Сandy tray Pop It: Draw an outline of a frame on thick cardboard to fit a candy tray. Cut the frame out and glue the candy tray to it. Now you can pop it!
An elastic bubble has two stable positions. If you apply too little force to the dome, it will return to its original position when released, since it is closer to it. By increasing the pressure and pushing the dome closer to its second stable position, you make this latter position more comfortable for it and force it to make the switch. The membrane jumps abruptly to the second position and stops, creating a pressure drop – a sound wave.
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Warning! Only under adult supervision.
Equipment: differently-colored alcohol-based markers, cotton disk, deep plate, milk.
Use markers to thoroughly saturate a cotton disk with ink, then toss the disk into a plate of milk: the milk becomes multicolored!
The marker ink permeates into the cotton fibers that make up the disk. As soon as the cotton disk comes into contact with the milk, some of the ink, which is less dense than the milk, floats to the surface. Surface tension stretches the ink into a thin film on the milk’s surface, as the dye molecules interact with the milk molecules more strongly than with each other.
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Warning! Only under adult supervision.
Equipment: several glasses, balloon, candle, plastic card, coins, thick cardboard, stapler.
Bet 1: Pour some water into a balloon and inflate it. Place a candle in a glass, light it, and cover the glass with the balloon. The candle will go out, and soon the balloon will be drawn into the glass. Now you can pick up the glass using the balloon!
Bet 2: Make a loop with thick paper and a stapler and place it on a narrow glass. Set a coin on top of the loop. Sharply pull the loop out from under the coin – the coin falls right into the glass!
Bet 3: Put a candle behind a glass and light it. Try to blow the candle out through the glass – it actually goes out!
Bet 4: Fill a glass to the brim with water. Place a plastic playing card on the surface of the water so that about half of it is suspended in the air. Balance a coin on the outer edge of the card – it remains steady!
Bet 5: Place a candle in a glass and light it. Thoroughly moisten a napkin with water and cover the glass with it. Press a second glass on top. The candle will go out and the glasses will cling to each other.
Bet 1: When the glass is covered with the balloon, its oxygen supply is cut off – the candle goes out, the air inside the glass cools down, and the pressure decreases. Atmospheric pressure pushes the balloon into the glass and presses the glass tightly against the balloon.
Bet 2: If you pull out the inner part of the ring, it stretches horizontally and shrinks vertically. In this case, the coin remains unsupported, with only gravity acting on it, and falls vertically downward. If you instead strike the outer part of the ring, it contracts horizontally and sharply increases vertically, instead catapulting the coin into the air.
Bet 3: Choosing the right obstacle is critical for this trick: it must have a streamlined shape like that of a cylindrical glass. When it meets the glass in its path, the air flow is divided and bends around it. The streams of air reunite behind the glass and extinguish the candle.
Bet 4: Surface tension prevents the card from lifting away from the surface of the water – it can even withstand a few coins!
Bet 5: When the glass’s oxygen supply is removed, the candle goes out. The air inside the glasses begins to cool down and the pressure decreases: atmospheric pressure reliably presses the glasses against each other. The napkin allows the pressure between the glasses to equalize, but at the same time seals the glasses by their edges.
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Warning! This experiment involves the use of small magnets. Only under adult supervision.
Equipment: PVA glue, contact lens solution, baking soda solution, thermochromic pigment, resealable bag, glass bowls.
Pour some PVA glue into a bowl and add a thermochromic pigment. In another bowl, combine a solution of baking soda with some contact lens solution. Pour the glue into the resulting mixture – it thickens instantly. And if you knead it with your hands, then it will begin to stretch and change colors!
PVA glue contains long molecules of polyvinyl alcohol, while contact lens solution contains a small quantity of boric acid. Under the influence of the baking soda, the boric acid binds the polyvinyl alcohol molecules together with weak chemical bonds. As a result, the mixture thickens and turns into slime! The thermochromic pigment, meanwhile, changes colors when the temperature rises. As you mold the slime, the heat from your hands causes it to change colors! Store the slime in a resealable bag in order to keep it for as long as possible.
Amazing and safe experiments await you in the MEL Chemistry subscription!
Warning! Only under adult supervision.
Equipment: cream (at least 30% fat), whisk, jug, refrigerator.
Pour some cream into a jug and leave it and a whisk in the refrigerator for half an hour. Then beat the cream with the whisk for a few minutes – the cream gradually turns yellow and thickens, forming butter.
Cream contains many droplets of fat. Each droplet consists of milk fat and special substances that make the walls of the droplets strong. Such substances are called phospholipids. When cooled, the milk fat partially freezes, forming sharp crystals that tear the walls of the droplets. This allows the droplets to stick together. For the droplets to collide more often, the cream must be intensively beaten. In just a few minutes, most of the droplets will combine to form your homemade butter!
Cool and safe experiments await you in the MEL Chemistry subscription!
Warning! Only under adult supervision.
Equipment: empty chip container, pushpin, optical-fiber cable, battery pack, wire connector, LED.
Carefully remove the insulation from an optical fiber and cut the fiber into small pieces (~ 10 cm / 4 inches). Use a pushpin to poke some holes in the lid of a chip container and insert a piece of the fiber into each hole. Connect a battery pack to an LED and place them in the container under the lid. Your night light is ready!
Unlike conventional cables, which employ electrical impulses, optical cables use light to transmit signals. Since light does not react to external electromagnetic fields, the signal is not distorted and data transmission is virtually uncompromised. In addition, optical fibers allow us to direct light along a convenient route. They operate based on the phenomenon of total internal reflection – when light moves from an optically denser medium to a less dense one, at more than a certain angle, it reflects entirely off their border. Total internal reflection minimizes losses as the signal is passed along.
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Warning! Only under adult supervision.
When the matches are heated, they ignite for a short time and release a lot of heat. Their wooden section begins to smolder, generating smoke, which in fact consists of very small, unburned wood particles. Alcohol mixed with this smoke burns out quickly, releasing enough heat to make these particles react with oxygen. The smoke thus burns completely, generating invisible water vapor and carbon dioxide.
Even more safe and cool experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
Equipment: sharp bamboo skewer, balloon.
Inflate a balloon and pierce it near the knot with a sharp bamboo skewer – it doesn’t burst!
Since the rubber that the balloon consists of is elastic, it can be stretched tremendously. When the balloon is pierced in places of high tension, an inhomogeneity appears on its surface, causing it to burst. In other words, when the balloon is inflated, each point on its surface is pulled in all directions; the tension that arises at the puncture site pulls the rubber apart from the puncture point. The air inside the balloon also affects the nature of the "explosion."
But there’s a cheat! The balloon won’t burst if you pierce it in the places of the least tension – at the knot and at the very tip of the balloon. The rubber tightly fits the bamboo stick, preventing the balloon from deflating quickly.
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Warning! Only under adult supervision
Equipment: glass, hot water, wax candle, paintbrush, watercolor paper, watercolor paints.
Put some candle wax in a glass and add hot water – the wax melts and floats to the surface. Dip a brush in the melted wax and use it to make an invisible painting on some watercolor paper. Now apply some watercolor paints to the paper – your hidden image appears!
Wax is mainly composed of fats and fatty acids, the molecules of which contain many groups of atoms consisting of carbon and hydrogen. Such groups don’t attract water molecules – in fact, they repel them. Therefore, water collects in droplets on the wax, either remaining on its surface or beading up and rolling off of it entirely. As watercolor paints mostly consist of water, they can’t permeate into the wax-covered sections of the paper, and your secret drawing is revealed instantly!
Cool experiments await you in the MEL Kids subscription!
Warning! Only under adult supervision.
Equipment: large container of water, two empty bottles, red and blue food coloring, two rubber stoppers, double-sided tape, two empty glasses.
Fill a bottle with hot water and tint the water red. Fill a second bottle with cold water and tint the water blue. Сlose the bottles with rubber stoppers and use double-sided tape to fix each bottle in a glass. Carefully place the glasses in a container of water and carefully remove the stoppers from the bottles. Observe as the cold (blue) water sinks and the hot (red) water rises!
If a solid body is less dense than water, buoyant force will cause it to float on the water’s surface. This is true for liquids as well! Water does not have a single, constant density – over a wide range of temperatures, the warmer water is, the lower its density, and vice versa. Therefore, hot water rises, and cold water sinks. The phenomenon when streams form due to temperature differences is called convection.
A similar experiment is included in the MEL Physics subscription!
Warning! Only under adult supervision.
Equipment: glass of warm milk, thermometer, funnel, gauze, white vinegar, tablespoon, food coloring, silicone ice molds.
Add four tablespoons of vinegar to a glass of warm milk (about 45 °C / 113 °F). White lumps of milk protein begin to form. Filter the protein out by pouring the liquid through a funnel with gauze. Take the protein and carefully squeeze out any excess moisture. Divide the resulting mass into two equal parts. Add a different food coloring to each half. Fill some silicone ice molds with the colorful mass and leave to dry for two days. You’ve made solid multicolored figurines! You can play with them or even use them to draw on asphalt or on a chalkboard!
Milk protein consists of casein and whey protein. Casein is evenly distributed throughout milk in the form of very, very small particles, which give the liquid its white color. With the application of heat and addition of acid, these particles clump together and combine with the whey protein to form a white mass of very large molecules. When this mass dries, it hardens like plastic. The moisture loss also causes the mass to decrease in size. The process yields a hard but rather fragile material, which you can draw with just like a crayon.
A similar experiment is included in the “Chemistry of materials” set from the MEL Chemistry subscription.
Warning! Only under adult supervision.
Equipment: 2 plastic bottles, 2 rulers, 2 balloons, bolt, nut, drill, cardboard, thread, paper straws.
Trace your hand and cut the drawing out. Use hot glue to attach some threads (tendons) to the fingertips and some pieces of straws (bones) to the hand. Pull the “tendons” – the hand contracts!
Make a muscle: bore a hole in a bottle cap, insert a silicone tube, and tape a balloon to the short end of the tube. Make several long vertical cuts in the plastic bottle. Insert the balloon into the bottle and screw the cap on – the muscle is ready! Make a second one the same way.
Hold two rulers together and drill a hole in them. Pull a thread through the tendon’s ligament and glue the “hand” to one of the rulers. Make another hole in the ruler and pull the thread through it. Fasten the rulers with a bolt and nut, and fix the muscles to the rulers using zip ties. Connect the tubes on the muscles with a splitter and pass the thread from the hand through the bottom of the first bottle and tie a knot. Attach the bicep to the second ruler the same way. Blow into the tube, inflating the balloons – the arm bends!
As they inflate, the balloons force the bottles to widen, which causes them to shorten. The “tendon” attached to the bottom of the bottle pulls the “forearm” along! Let the balloons deflate – the arm will unbend. Human biceps work similarly: the muscle shortens as it contracts, and the tendon thus pulls the forearm upward, bending the arm.
More exciting experiments are waiting for you in the MEL Kids subscription!
Warning! Only under adult supervision.
Equipment: thread, double-sided tape, metal paper clip, neodymium magnets, cardboard box, astronaut drawing, paintbrush, blue paint.
Paint a box blue and let it dry. Optionally, you can decorate it with stars. Attach a neodymium magnet to the top of the box with double-sided tape. Make an astronaut: pass a thread through a paper clip, cut out a drawing of an astronaut, and attach it to the paper clip along with a second neodymium magnet. You’ll ultimately achieve "weightlessness" by choosing the length of the thread: if the thread is too short, the astronaut will fall. Fix the free end of the thread at the base of the box and release your astronaut! If you cut the thread, the astronaut will be pulled to the magnet.
The strength of the interaction of two magnets depends on the distance between them: the closer two magnets are to each other, the greater the strength of their interaction. When the magnetic force acting on the “astronaut's” magnet becomes greater than the force of gravity acting on the astronaut and its magnet, they will be suspended in midair. The thread holds the astronaut in place, preventing it from being pulled all the way to the magnet at the top of the box.
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Warning! This experiment involves the use of small magnets. Only under adult supervision.
Equipment: plate, bowl, glass, tablespoon, vinegar, table salt, old copper coin.
Dissolve two tablespoons of table salt in a glass of vinegar. Pour the solution into a bowl and immerse an old copper coin in it – it brightens rapidly before your eyes!
Old copper coins are covered with films of a mixture of copper(I) oxide and copper(II) oxide. Such films cannot be dissolved in vinegar or a solution of sodium chloride separately, but they rapidly react with a mixture of vinegar and salt. Copper(II) oxide dissolves in acetic acid, forming copper(II) acetate:
2CH₃COOH + CuO → (CH₃COO)₂Cu + H₂O
And copper(I) oxide reacts with sodium chloride, forming chloride complexes:
Cu₂O + 2NaCl + 2CH₃COOH → 2Na[CuCl₂] + 2CH₃COONa + H₂O
These processes must happen simultaneously, so the coin cannot be cleaned by rinsing first with vinegar, then with a salt solution, or vice versa. Rinse your coin with water after the experiment to ensure that it retains its shine for a long time!
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Warning! Only under adult supervision.
Equipment: two forks, two toothpicks, cork.
Intertwine the tines of two forks and insert a toothpick between them. Insert a second toothpick into a cork and set the construction on the toothpick, establishing a fulcrum for balance. Surprisingly, this balance will be stable! You can even make the forks rotate around the support.
A body is in equilibrium if all the forces that tend to move or rotate it (e.g. gravity and support reaction force) are compensated. When talking about the balance of our construction, we must consider not only the value of the forces acting on it, but also their points of application. Gravity acts on each part of the construction, but we can consider that it applies to the object’s center of mass. The position of the center of mass of a composite body depends on the relative location and masses of its parts, and may even be located outside of the body, as in our construction. If the construction is to stay balanced as it rests on the support, its center of mass must be on the same vertical line as the fulcrum. But that’s not all! It’s not enough to obtain balance: it must be stable! For the construction to be stable, it must be able to return from small deviations from the position of equilibrium, for example, when we gently strike one of the forks. For a body resting on one point, this means that the center of mass must lie below the fulcrum as well as on the same vertical line with it. The complex shape of our construction fulfills both of these conditions.
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Warning! Only under adult supervision.
The burner flame consists of a heating zone, an intensive combustion zone, and a luminous zone. In the heating zone, hydrocarbon gases and oxygen are heated by the surrounding blue flame, but do not react with one another. Therefore, this part of the flame is colorless and is located at the bottom, and its temperature reaches about 350 °C (660 °F). Passing into the intense combustion zone, the gases react, releasing a blue glow and a lot of heat. This is the hottest part of the flame, with a temperature of approximately 1500 °C (2730 °F). The blue color is due to the formation of radicals such as OH and CH. These radicals are highly unstable and do not exist under normal conditions; they appear at high temperatures. In the flame, these radicals are in an excited state, that is, they have an excess of energy. In an effort to move to a more stable, ground state, these particles release energy in the form of blue light. Some gas molecules do not burn completely, forming small particles of soot. These particles rise higher and are oxidized by oxygen, heating up to about 1000 °C (1830 °F) and emitting yellow light. The flame of the burner can be used to detect metal ions: they absorb the thermal energy of the flame, which is then emitted in the form of light with a characteristic color. For example, copper(II) ions emit green light, sodium ions emit yellow light, and calcium or strontium create shades of red. In addition, the flame’s temperature is high enough to melt glass, causing it to bend and stretch. This time, the flame turns yellow-orange due to the sodium and calcium oxides presence in the glass.
Safer (but just as cool) experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
Equipment: cup of water, dental cotton roll, dark green/dark red/black felt-tip pens, filter paper, scissors, pencil, thread.
Draw a small circle in the center of a disk of filter paper with a green felt pen. Soak a dental cotton roll in a cup of water and place it in the middle of the green circle – over the course of a few minutes, an elegant pattern of several colors emerges. Optionally, you can trim this filter paper into the shape of a light bulb containing the resulting pattern and draw a base on it with a pencil. You can string a set of such “bulbs” and make your own creative holiday lights! If you alternate with using dark red or black felt pens, your string of festive lights will be multicolored!
As it turns out, a dark green felt pen (just like dark red or black) is composed of several colored compounds that combine to produce dark green. The molecules of these substances have different chemical natures and, as a result, interact with paper in different ways: some of them move through paper more quickly, and some more slowly. We can observe this using the capillary effect: the water we add moves evenly through the filter paper, carrying the dyes with it. This separation technique is called paper chromatography. However, the composition of these felt-tip pens can vary depending on the manufacturer – if the experiment doesn’t work with one particular dark green marker, try another one!
A similar experiment is included in the MEL Science subscription!
Warning! Only under adult supervision
Equipment: large container with water, empty bottle, coins, electrical tape, silicone tube, balloon, rubber stopper, drinking straw, scissors, hot glue.
Make holes in the top and bottom of a plastic bottle. Bore another hole in the middle of the cap and pass a silicone tube through it. Put a balloon on the end of the tube and seal it with electrical tape. Insert the balloon into the makeshift “submarine” and cap it. Use electrical tape to attach a ballast of coins to the bottom of the submarine, glue a rubber stopper on top with hot glue, and insert a straw. Your submarine is ready!
Use a syringe to supply air through the tube – inside the “submarine,” the balloon inflates. When placed in an aquarium with water, the “submarine” stays on the surface. By removing air from the balloon with the same syringe, you can make it sink. You can control its diving depth this way!
When a body is placed in a liquid, a buoyant force proportional to the volume of the immersed part of the body acts on it. If the buoyant force exceeds the force of gravity, the body will float on the surface. When the bottle is filled with water, its volume remains unchanged, but its mass increases. At a certain moment, the force of gravity exceeds the buoyant force, acting on the submarine and causing it to sink. When air is supplied, the balloon inside the submarine inflates and displaces the water, which reduces the force of gravity acting on the bottle, and when the force of gravity becomes less than the buoyant force – the submarine rises to the surface.
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Warning! Only under adult supervision.
Sulfur molecules and crystals can have a variety of structures. Sulfur molecules can contain five atoms (S₅), eight atoms (S₈), or even more. In turn, the same molecules (for example, S₈), like construction toys, can be assembled in different ways: depending on how they are “stacked,” they’ll create solids with different structures. Solid sulfur powder consists of S₈ molecules that are folded in a special way, forming so-called rhombic sulfur. When the powder is heated, a yellow liquid of the same composition is formed. However, excess heat causes some of the molecules to polymerize, forming S₁₆, S₂₄, etc. and creating orange spots. A metal paper clip quickly absorbs the heat, and the sulfur crystallizes immediately. However, the molecules arrange themselves in a different way to how they started, forming so-called monoclinic sulfur. This creates a strong disc with a darker yellow hue than that of the powder. The molecules find this arrangement “inconvenient,” and rearrange over the course of several minutes (scientists call such structures metastable). This causes the disc to brighten noticeably and become so fragile that it is easy to break with three fingers!
Safe and cool chemical experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
Equipment: glass container with lid, glass, double-sided tape, message.
Fill a glass tank approximately halfway full with water. Tape a message to the bottom of a glass and fix the bottom of the glass to the inner side of the lid of the glass tank using double-sided tape. Gently close the lid, immersing the glass, upside down, in the water. When you open the lid and retrieve the glass from the water, you’ll see that the message inside is still dry! You can prove the presence of air in the glass by covering a candle with the glass and repeating the process – the candle will continue to burn, despite the fact that the liquid level outside the glass is higher than the flame.
When the glass is immersed in water, it contains air. Water tends to push light air upward, compressing it and trapping it inside the glass, which prevents the water itself from rising to fill the glass. Your message is safely hidden inside this air pocket!
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Warning! Only under adult supervision.
Equipment: hot solutions of copper(II) sulfate and sodium citrate, beaker, funnel, filter paper, Petri dish, sheet of metal, matches, paper stencil.
Add a hot solution of sodium citrate to a hot solution of copper(II) sulfate. Observe as a copper(II) citrate precipitate gradually forms. Filter it out and leave it to dry for 24 hours – it will turn into a beautiful turquoise powder. Arrange it in a paper stencil on a sheet of metal and touch it with a burning match. The copper(II) citrate will gradually turn black.
When heated, copper ions are reduced, taking electrons from citrate ions, and turn into very small particles of metallic copper. Unlike a sizable piece of copper, these particles are easily oxidized by atmospheric oxygen, releasing heat and forming black copper(II) oxide. The heat this generates keeps the process going, so even a small amount of heat is enough to cause the decomposition of the entire copper(II) citrate pile.
A similar experiment is included in the “Copper” set from the MEL Chemistry subscription!
Warning! Only under adult supervision.
Hydrogen peroxide is a very active compound and can be both an oxidizer and a reducing agent. In this process, it reduces iodic acid to form molecular iodine and a so-called triiodide complex. This process can be simplified to the following chemical reactions:
HIO₃ + 3H₂O₂ → HI + 3O₂↑ + 3H₂O
5HI + HIO₃ → 3I₂ + 3H₂O
HI + I₂ → H[I₃]
Since oxygen is formed during the first reaction, we can observe the emergence of the gas. The iodine and triiodide complex turn the solution amber. But the solution immediately turns blue, since the starch molecules, which are very long and look like spirals, trap iodine molecules like a fishnet, forming a deep blue iodine-starch complex. Under the action of malonic acid, this complex is destroyed, since it reduces iodine molecules, while the solution itself becomes colorless:
C₃H₄O₄ + I₂ → C₃H₃O₄I + HI
The process repeats every few seconds, and the reaction period depends on the concentrations of the initial solutions. What is this if not a chemical clock?
Fun and safe experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
A safer version of this experiment is included in the “Chemistry of eggs” set from the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
Equipment: two small glasses, soda, two galvanized screws, two copper coins, crocodile clips, digital alarm clock.
Connect a copper coin to a galvanized screw using a crocodile clip. Put the coin in one glass, and fix the screw to the wall of a second glass. Using crocodile clips, connect another screw to the “–” terminal of a digital clock, and another coin to the “+” terminal. Put the second coin in the glass with the first screw, and fix the second screw on the wall of the glass with the first coin. When the glasses are filled with soda, the clock starts working!
Metal screws are often coated with zinc to prevent them from reacting with substances from their environment (for example, oxygen and water) via a phenomenon known as corrosion. Such screws are said to be “galvanized.” Meanwhile, soda contains what is known as acidity regulators, often either citric or phosphoric acid. These substances make the acidity of the drink suitable for our bodies. When the circuit is closed, these acidity regulators react with zinc and copper, electric current begins to flow through the circuit, and the clock starts working! The galvanized screws can be replaced with another metal, such as iron, but this will diminish the voltage of the “battery” as iron is less chemically active than zinc. You can confirm this by comparing the positions of zinc and iron in the electrochemical series.
Exciting experiments await you in the MEL Chemistry subscription!
Warning! Only under adult supervision.
Equipment: transparent bottle (0.5 L or 16.5 fl oz) with cap, star confetti, water, glycerol (0.25 L or 8.25 fl oz).
Fill a bottle with water, pour some star confetti into it, cap it, and shake – the sparkles swirl up but rapidly settle to the bottom. Carefully pour out about half of the water and top the bottle up with glycerin. Close the bottle and shake it again – this time the confetti settles much more slowly, creating a real blizzard!
The higher the viscosity of the liquid, the more the friction force slows down the movement of the confetti in it. Water has relatively low viscosity, so the confetti quickly settles to the bottom. However, you can significantly increase the friction force by adding a much more viscous liquid that mixes well with water – glycerol. Now the confetti settles much more slowly, and you can trace how each tiny star moves in this starry blizzard!
More fun experiments for the whole family await you in the MEL Kids subscription!
Warning! Only under adult supervision.
Equipment: used (clean) polystyrene container, whiteboard markers, scissors, letter opener, cutting board, thread, nail polish, oven.
Cut the lid off of a polystyrene container and draw your shape of choice on it. Cut your shape out, make two holes in it with a letter opener, and color it with whiteboard markers. Put it in the oven at 180 °C (360 ° F) for approximately one minute. It should shrink! Now you can put it on a thread and hang it on your keyring – it makes for a cute keychain! If necessary, coat your new keychain with nail polish.
As polystyrene containers are produced, the structure of the polystyrene is changed significantly. The molecules of the polymer are stretched and arranged randomly within its structure (such structures are referred to as “amorphous”), which is what makes it possible to form large pieces of plastic. Heating polystyrene returns it to its original shape: the elongated polystyrene molecules begin to curl up and assume a coil-like form. As a result, the structure of the plastic becomes more ordered, and its rigidity increases.
Amazing and exciting experiments await you in the MEL Chemistry subscription!
Warning! Only under adult supervision.
Equipment: cup, hibiscus tea, baking soda, watercolor paper, q-tip.
Make a cup of strong hibiscus tea and prepare a saturated baking soda solution. Apply the baking soda solution to a section of watercolor paper and leave the paper to dry overnight. The tea’s color will deepen overnight as well. The next day, dip a q-tip in the tea and start drawing on the prepared paper – part of the drawing will remain red and part of it will turn blue.
Hibiscus tea contains natural dyes called anthocyanins. Anthocyanins’ structure and color depend on whether they are in an acidic or alkaline medium. Hibiscus tea is acidic, which makes the anthocyanins tint the drink red. Baking soda, on the other hand, creates an alkaline environment and thus changes the anthocyanins’ structure. As a result, the tea turns blue.
More fun experiments await you in the MEL Kids subscription!
Warning! Only under adult supervision.
Equipment: glass, glue, pine cone, boiling water.
Glue a pine cone to the bottom of a glass and fill the glass with boiling water – in about half an hour, the cone’s scales will press noticeably towards its center, and the cone will close! But not permanently: if you leave it to dry, it will reopen in about two days!
Most of the water that the cone absorbs ends up in the scales. Each scale has two layers – an inner layer and an outer layer. As they absorb water, the scales’ layers expand, the outer layer more dramatically than the inner one. The change in the scales’ specific shape presses them towards the center of the cone. Thus, the cone closes as it absorbs water. If you leave it in the open air, the process will reverse – the scales will start to dry out and shrink, the outer layer again more so than the inner one, forcing the scales to unfurl and allowing the cone to reopen. Similar processes allow pine cones to protect their seeds from excess moisture in their natural environment.
Safe and fun experiments for the whole family are waiting for you in the MEL Kids subscription!
Warning! Only under adult supervision
Equipment: calcium nitrate, graphite dust, beaker with water, wooden stick, paintbrush, LEDs, 9 V battery, crocodile clips.
Prepare an aqueous solution of calcium nitrate in a beaker and add some graphite dust to create electrically conductive ink. Use this ink to draw a snowflake. Connect a 9 V battery to the snowflake with crocodile clips and put LEDs on the graphite lines to create a complete circuit – the LEDs light up!
Graphite has a special structure consisting of flat layers of carbon. Electric current can flow along these layers. Adding an electrolyte solution to its powder makes electrically conductive ink. An electrolyte is a substance that dissociates into charged particles (ions) in an aqueous solution, and therefore can also conduct electric current. Calcium nitrate is a perfect example. The electrolyte solution helps electrons move from one particle of graphite to the next. Thus, a thick mass is obtained, which you can use to make real liquid "wires" in an electrically conductive pattern!
A similar experiment is included in the “Zinc-carbon battery” set from the MEL Chemistry subscription!
Warning! Only under adult supervision.
Equipment: sodium carbonate, citric acid, ammonium iron(III) sulfate, potassium hexacyanoferrate(III), beaker, cotton roll, watercolor paper, negative image, hair dryer.
Dissolve sodium carbonate, citric acid, ammonium iron(III) sulfate, and potassium hexacyanoferrate(III) in water to create a light-sensitive mixture. Use a cotton roll to apply this solution to a piece of watercolor paper, then cover the paper with a negative image and set the paper and negative under a lamp. After 10 minutes, remove the negative image and rinse the paper with water, then dry it with a hair dryer – you’ve made a cute winter postcard!
Under the influence of bright light, the iron(III) ions in the photosensitive mixture begin to actively enter an excited state. At the same time, they oxidize citric acid ions, resulting in the formation of a complex mixture of organic substances and iron(II) ions, with which potassium hexacyanoferrate(III) forms an insoluble blue compound:
Fe²⁺ + K₃[Fe(CN)₆] → KFe[Fe(CN)₆]↓ + K⁺
This compound is firmly fixed in the pores of the paper, so when rinsed with water, the blue pattern remains!
A similar experiment is included in the “Cyanotype” set from the MEL Chemistry subscription.
Warning: only under adult supervision.
Equipment: diapers, scissors, table salt, glasses, spoon.
Cut a few diapers and pour their filler into a glass. Fill a plate with water and pour the filler on it – the filler absorbs most of the water and increases dramatically in size, beginning to resemble snow. Fill a glass with this "snow," add three teaspoons of table salt, and stir with a spoon – the snowdrift “melts” into a cloudy liquid.
Sodium polyacrylate’s long molecules contain many carboxyl groups. These carboxyl groups attract a lot of water, which causes the sodium polyacrylate powder to swell and increase significantly in size. This effect is reversible: when table salt is added, osmotic pressure arises, which draws the water molecules out of the structure of sodium polyacrylate – yielding liquid once again!
A similar experiment is included in the “Chemistry of winter” set from the MEL Chemistry subscription.
Warning! Only under adult supervision
Equipment: glass bottle with cap, water, isopropyl alcohol, sodium chloride (salt), food coloring.
Mix some isopropyl alcohol and water in a bottle to create a homogeneous liquid. Add salt and food coloring and shake the mixture well – the liquid readily separates into alcohol and water, and the water is tinted more vividly than the alcohol.
Alcohol and water will mix with each other in any ratio. Sodium chloride dissolves well in water, but poorly in alcohol. When salt is added to the prepared solution, it attracts water molecules to itself, “distracting” them from the alcohol molecules. As a result, when the mixture is shaken, the alcohol molecules separate from the water to form a second layer of liquid. Since water is more dense than alcohol, the water winds up at the bottom. The water is also tinted more vividly because food coloring, like salt, dissolves better in water.
More entertaining experiments await you in the MEL Physics subscription!
Warning! Only under adult supervision.
Equipment: beaker, chicken eggs, copper(II) sulfate solution, pipettes, wooden stick, Petri dish, sodium hydroxide solution.
A few egg whites are separated from their yolks and a few drops of copper(II) sulfate solution are added. Light blue threads form in the mixture. The mixture is poured into a Petri dish and some sodium hydroxide solution is added – and the mixture turns purple!
Egg white contains ovalbumin protein. Copper(II) sulfate forms an insoluble compound with it, which creates the light blue threads you observe. When sodium hydroxide is added, the copper and ovalbumin compound breaks down into smaller molecules, which give the solution its purple color.
A safer version of this experiment is included in the “Chemistry of eggs” set from the MEL Chemistry subscription.
Attention! All experiments are performed by professionals. Do not attempt!
Equipment: toaster, frying pan, bread, vegetable oil, potatoes.
If you toast a slice of bread for a minute, it turns out golden and crisp. When you peel some potatoes and fry them in a greased frying pan, they also turn a beautiful golden-brown after a while. Why?
All foods contain proteins and carbohydrates. When heated, these compounds partially decompose to amino acids and sugars. Amino acid molecules contain special fragments (amino groups), as do sugars (aldehyde groups). Due to these fragments, amino acids and sugars react in what is known as the Maillard reaction to form hundreds of new compounds, which are responsible for the crispness and pleasant aroma of cooked food. This reaction has been studied for more than a hundred years, but the exact compositions of all the products of this reaction have not yet been established.
Cool and safe experiments await you in the MEL Chemistry subscription!
Warning! Only under adult supervision
Equipment: zinc wire, thread, wooden stick, tin(II) chloride, sodium hydrogen sulfate, glass container, beaker of water.
Dissolve some tin(II) chloride and sodium hydrogen sulfate in a beaker of water, then transfer the solution to a larger glass container. Bend a zinc wire into the shape of a tree and suspend it in the container by a thread tied to a wooden stick. In a few minutes, the tree is covered in fluffy “snow”!
Zinc is located to the left of tin in the reactivity series, meaning that it is chemically more active and easily takes part in redox reactions with solutions of tin(II) salts. In this case, the tin moves from the solution to a metallic state, forming beautiful crystals on the surface of the zinc wire:
SnCl₂ + Zn → Sn↓ + ZnCl₂
A similar experiment is included in the “Chemistry of winter” set from the MEL Chemistry subscription.
Attention! Only under adult supervision.
Equipment: glass container with sodium silicate solution, nickel(II) sulfate.
Drop some nickel(II) sulfate crystals into a glass container with a solution of sodium silicate. In 20 minutes, vertical green sticks resembling trees form.
Once the nickel(II) sulfate crystals enter the solution, they are immediately covered with a brittle green film of nickel(II) silicate:
NiSO₄ + Na₂SiO₃ → NiSiO₃ ↓ + Na₂SO₄
There are many cracks in this film, and they allow the reaction to continue and build upon itself. In 20 minutes, enough nickel(II) silicate forms to make large green sticks.
A similar experiment is included in the "Artificial Sea" set from the MEL Chemistry subscription!
Warning: only under adult supervision.
Equipment: sodium silicate, solutions of copper(II) chloride and nickel(II) sulfate, Petri dish, pipettes.
Add a few drops of copper(II) chloride and nickel(II) sulfate solutions to a solution of sodium silicate. The droplets don’t spread through the sodium silicate, but rather remain on the surface, forming neat-looking artificial jellyfish.
Due to the high viscosity of the sodium silicate solution, the droplets don’t spread over its surface or mix with it, but instead splash and spatter somewhat like paint capsules falling on asphalt. At the same time, reactions begin between the compounds in the droplets and the sodium silicate solution:
CuCl₂ + Na₂SiO₃ → CuSiO₃↓ + 2NaCl
NiSO₄ + Na₂SiO₃ → NiSiO₃↓ + Na₂SO₄
CuCl₂ + Na₂SiO₃ + H₂O → Cu(OH)₂↓ + 2NaCl + SiO₂↓
Such reactions proceed relatively quickly, yielding a film of insoluble compounds between each droplet and the sodium silicate solution. Thus the droplets do not spread, instead beginning to resemble jellyfish.
A similar experiment is included in the MEL Chemistry subscription!
Warning! Only under adult supervision.
Magnesium strips are dropped in a flask with a solution of tartaric acid and the flask is covered with a balloon. When the balloon is completely filled with the gas forming in the flask, it is tied with a thread with an attached screw-nut – and the balloon floats! If touched with a burning match, the balloon will explode.
Magnesium and tartaric acid react to release hydrogen gas:
C₄H₆O₆ + Mg → MgC₄H₄O₆ + H₂↑
Hydrogen gas is 15 times lighter than air, and therefore a balloon filled with it can float. It explodes if exposed to flame due to the violent reaction between hydrogen and oxygen, which forms water:
2H₂ + O₂ → 2H₂O
The energy released in this reaction can safely be utilized to power so-called hydrogen vehicles.
Amusing and safe experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
An electrode with a positive charge is called an anode because it attracts particles with a negative charge (anions). An electrode with a negative charge is called a cathode as it attracts particles with a positive charge (cations). Therefore, the green strip of the starting material is divided in two – a blue segment consisting of copper cations and a yellow segment consisting of chromate anions. When we change the polarity of the electrodes, we simultaneously switch their charges – and the stripes begin to move in opposite directions. This is how ionic races go!
Cool and safe experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
Equipment: plastic bottle, rice, funnel, chopstick.
Fill a plastic bottle to the brim with rice. Then, closing the opening with one hand, tap the bottle on the table several times to make the rice settle in place. The volume of rice in the bottle should decrease. Add more rice and tamp it down again. Then insert a chopstick into the rice and try to pull it back out again. The stick lifts the bottle easily!
Frictional force arises when two bodies come into contact and interferes with their movement relative to each other. In this experiment, the chopstick and the rice are two such bodies. When the rice is tamped down, it becomes quite dense, and when the chopstick is inserted the rice has nowhere to go: the bottle limits its movement. The rice squeezes the stick firmly from all sides and a strong frictional force arises, which is capable of supporting the bottle. It is worth noting that frictional force also arises if the rice is uncompressed, but it is much weaker, because the uncompressed rice presses less on the stick.
Cool experiments await you in the MEL Physics subscription!
Safety precautions: Warning! Only under adult supervision
Equipment: alkaline luminol solution, thick paper, q-tip, ozonizer.
A q-tip is dipped in an alkaline luminol solution and is used to draw a ghost on a piece of thick paper. The lights are turned off and a stream of ozone is directed at the drawing – the drawing glows blue!
Ozone oxidizes luminol. In the process, energy is released as a blue glow.
A safer version of this experiment is included in the “Chemistry & light” set from the MEL Chemistry subscription
Attention! All experiments are performed by professionals. Do not attempt.
Equipment: pumpkin-shaped candlestick, 25 g (1 Tbsp) baking soda (sodium bicarbonate), 75 mL (7 Tbsp) white vinegar (acetic acid solution), food coloring, wooden stick.
Separate an egg’s white from its yolk and pour the white into a pumpkin-shaped candlestick. Add baking soda and stir with a wooden stick. Mix some vinegar and food coloring and add the mixture to the candlestick. Colorful foam bursts out of the pumpkin when the mixture is stirred with the wooden stick!
Sodium bicarbonate and acetic acid react to form gaseous carbon dioxide. As it emerges, the gas is trapped by the relatively thick egg white, thus frothing the mixture. You can use different food colorings to make foam with all sorts of different colors!
A similar experiment is included in the “Chemistry of eggs” set from the MEL Chemistry subscription.
Warning! Only under adult supervision
Equipment: heater, tray, cork stands, solid fuel, beaker, aluminum foil, calcium chloride, sodium acetate.
A heater is set on a tray with cork stands. Calcium chloride and sodium acetate are measured into a beaker, which is then covered with aluminum foil and heated with solid fuel. After the beaker cools, the foil is removed and a lit match is lowered into the beaker – and a flame flares up!
Heating calcium chloride with sodium acetate produces sodium chloride and calcium acetate:
2CH₃CO₂Na + CaCl₂ ⇄ 2NaCl +(CH₃CO₂)₂Ca
The latter then decomposes upon further intense heating:
(CH₃CO₂)₂Ca → CaCO₃ + (CH₃)₂CO
This also produces a volatile and flammable substance – acetone. Its vapor burns easily when a burning match is lowered into the beaker:
(CH₃)₂CO + 4O₂ → 3CO₂ + 3H₂O
Calcium acetate can also be used to make a flammable gel. For a similar experiment, see the link.
Safe experiments await you in the MEL Chemistry subscription!
Safety precautions: Attention! All experiments were performed by professionals. Do not attempt.