Light a light bulb with... a lemon!

Complexity:

Danger:

Do this experiment at home

Safety

Before starting the experiment, put on protective gloves and goggles.

Conduct the experiment on a tray.

General safety rules

• Do not allow chemicals to come into contact with your eyes or mouth.
• Keep people away from the experiment site without protective glasses, as well as small children and animals.
• Keep the experimental kit out of the reach of children under 12 years of age.
• Wash or clean all equipment and fixtures after use.
• Ensure that all reagent containers are tightly closed and stored properly after use.
• Make sure all disposable containers are disposed of correctly.
• Use only the equipment and reagents provided in the kit or recommended by current instructions.
• If you have used a food container or glassware for experiments, throw it away immediately. They are no longer suitable for storing food.

First aid information

• If reagents come into contact with your eyes, rinse thoroughly with water, keeping the eye open if necessary. Contact your doctor immediately.
• If swallowed, rinse mouth with water and drink some clean water. Do not induce vomiting. Contact your doctor immediately.
• If reagents are inhaled, remove the victim to fresh air.
• In case of skin contact or burns, flush the affected area with plenty of water for 10 minutes or longer.
• If in doubt, consult a doctor immediately. Take the chemical reagent and its container with you.
• In case of injury, always seek medical attention.

• Improper use of chemicals can cause injury and damage to health. Carry out only the experiments specified in the instructions.
• This set of experiences is intended for children 12 years and older only.
• Children's abilities vary significantly even within age groups. Therefore, parents conducting experiments with their children should use their own discretion to decide which experiments are appropriate and safe for their children.
• Parents should discuss safety rules with their child or children before experimenting. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
• Before starting experiments, clear the experiment site of objects that may interfere with you. Avoid storing food near the test site. The testing area should be well ventilated and close to a tap or other water source. To conduct experiments, you will need a stable table.
• Substances in disposable packaging must be used completely or disposed of after one experiment, i.e. after opening the package.

FAQ

The LED is not lit. What to do?

First, make sure that the slices in the lemon are not touching each other.

Secondly, check the quality of the connection between the crocodile clips and the metal plates.

Thirdly, make sure that the LED is connected correctly: the black crocodile is attached to the short “leg”, the red one to the long one. In this case, the crocodiles should not touch the other “leg”, otherwise the circuit will close!

The juice near the magnesium plate hisses. This is fine?

Everything is fine. Magnesium is a reactive metal and reacts with citric acid to form magnesium citrate and release hydrogen.

Other experiments

Step-by-step instruction

1. Take 2 magnesium plates from the jar labeled “Mg”.
2. Prepare 2 alligator clips: 1 black and 1 white. Connect the magnesium plates to the black and white crocodiles.
3. Take 2 copper plates from the jar labeled "Cu".
4. Connect the copper strip to the free end of the white crocodile. Connect the copper plate to the red crocodile.
5. Cut the lemon in half. Insert copper and magnesium strips into one half of the lemon at a short distance from each other (about 1 cm). Repeat with the remaining two slices, using the other lemon half. Make sure the plates are not touching.
6. Take the LED. Connect the free end of the red crocodile to the long leg of the LED. Connect the free end of the black crocodile to the short leg of the LED. The LED will light up!

Disposal

Dispose of solid waste from the experiment along with household waste. Drain the solutions into the sink and then rinse thoroughly with water.

What happened

Why does the diode start to glow?

Under the experimental conditions, a chemical reaction occurs: electrons from magnesium Mg are transferred to copper Cu. This movement of electrons is an electric current. As it passes through the LED, it causes it to glow. Thus, the installation assembled in this experiment acts like a battery - a chemical source of current.

To learn more

The participants in this experiment - copper Cu and magnesium Mg - are very similar. Both of them are metals. This means that they are quite malleable, shiny, and conduct electricity and heat well. All these properties are consequences of the internal structure of metals. It can be thought of as positive ions arranged in a certain order, which are held together using electrons common to the entire piece of metal. It is because of this commonality that electrons can “walk” throughout the entire volume of the metal.

Despite the common motifs in structure, copper and magnesium are different from each other. The overall “pack” of electrons is held in a piece of copper more strongly than in the case of magnesium. Therefore, purely theoretically, we can imagine a process in which electrons from magnesium “escape” to copper. However, this will lead to an increase in charges: positive in magnesium and negative in copper. This cannot continue for long: due to mutual repulsion, it will be unprofitable for negatively charged electrons to move further into copper. The charge is thus collected at the contact surface of two different metals.

Interestingly, the extent to which electrons are transferred from one metal to another depends on temperature. This connection is used in electronic devices that measure temperature. The simplest such device that uses this effect is thermocouple. The use of thermocouples is now widespread, and they form the basis of electronic thermometers.

Let's return to our experience. In order for electrons to constantly transfer from magnesium to copper, and for the process to become irreversible, it is necessary to remove the positive charge from magnesium and the negative charge from copper. This is where lemon comes into play. It is important what kind of environment it creates for the copper and magnesium plates stuck into it. Everyone knows that lemon has a sour taste mainly due to the citric acid it contains. Naturally, there is also water in it. A solution of citric acid is capable of conducting electricity: when it dissociates, positively charged hydrogen ions H + and a negatively charged citric acid residue appear. This environment is ideal for removing the positive charge from magnesium and the negative charge from copper. The first process is quite simple: positively charged magnesium ions Mg 2+ pass from the surface of the magnesium plate into the solution (lemon juice):

Mg 0 – 2e - → Mg 2+ solution

The second process takes place on a copper plate. Since it accumulates a negative charge, it attracts hydrogen ions H + . They are able to take electrons from a copper plate, turning first into H atoms, and then almost immediately into H 2 molecules, which fly away:

2H + + 2e - → H 2

Why can’t we get by with just one copper-magnesium pair?

The closest analogue of the “copper plate – lemon – magnesium plate” system is an ordinary AA battery. It works on the same principle: chemical reactions occurring inside it lead to the generation of a current of electrons, that is, electricity. You've probably noticed that in some devices AA batteries are arranged in a row (that is, the negative pole of one is in contact with the positive pole of the other). More often they do this not directly, but through wires or small metal plates. But the essence remains the same - this is necessary to increase the force that acts on the electrons, and therefore to increase the current.

Likewise, the copper plate in one piece of lemon is connected to the magnesium plate of another. If you connect a diode with only one copper-magnesium pair, it will not start to glow, but using two pairs leads to the desired result.

To learn more

To describe the force that causes charges to move, that is, leads to the generation of electricity, the concept is used voltage. For example, any battery indicates the voltage value that it can create in a device or conductor connected to it.

The voltage created by one magnesium-copper pair is not enough for this experiment, but two pairs are already enough.

Why do we use copper and magnesium? Is it possible to take some other pair of metals?

All metals have different abilities to hold electrons. This allows you to arrange them in the so-called electrochemical series. Metals that are to the left in this row hold electrons worse, and those that are to the right hold electrons better. In our experience, the electric current arises precisely because of the difference between copper and magnesium in their ability to hold electrons. In the electrochemical series, copper is significantly to the right of magnesium.

We can easily take two other metals - it is only necessary that there is a sufficient difference between their desire to retain electrons. For example, in this experiment, silver Ag can be used instead of copper, and zinc Zn can be used instead of magnesium.

However, we chose magnesium and copper. Why?

Firstly, they are very affordable, unlike silver. Secondly, magnesium is a metal that simultaneously combines sufficient activity and stability. Like alkali metals - sodium Na, potassium K and lithium Li - it is easily oxidized, that is, it gives up electrons. On the other hand, the surface of magnesium is covered with a thin film of its oxide MgO, which is not destroyed when heated up to 600 o C. It protects the metal from further oxidation in air, which makes it very convenient to use in practice.

What other fruits and vegetables can be used instead of lemon?

Many fruits and vegetables are suitable for this experiment. It is enough just for them to have juicy pulp. For example, instead of lemon, you can take an apple, banana, tomato or potato. Even a large grape will do!

All these vegetables, fruits and berries contain enough water, as well as substances that dissociate (break up into charged particles - ions) in water. Therefore, electric current can flow through them too!

What is a diode and how does it work?

Diodes are small devices that can pass electric current through themselves and perform some useful work. In this case, we are talking about an LED - when an electric current passes, it glows.

All modern diodes contain a semiconductor at their core - a special material whose electrical conductivity is not very high, but can increase, for example, when heated. What is electrical conductivity? This is the ability of a material to conduct electric current through itself.

Unlike a simple piece of semiconductor, any diode contains two “grades” of it. The very name “diode” (from the Greek “δίς”) means that it contains two elements - they are usually called anode And cathode.

The diode's anode consists of a semiconductor containing so-called "holes" - areas that can be filled with electrons (actually empty shelves specifically for electrons). These “shelves” can move quite freely throughout the anode. The cathode of the diode also consists of a semiconductor, but a different one. It contains electrons, which can also move relatively freely through it.

It turns out that this diode composition allows electrons to easily move through the diode in one direction, but practically does not allow them to move in the opposite direction. When electrons move from the cathode to the anode, at the boundary between them there is a meeting of “free” electrons in the cathode and electron vacancies (shelves) in the anode. Electrons happily occupy these vacancies, and the current moves on.

Let's imagine that the electrons are moving in the opposite direction - they need to get off the cozy shelves into a material where there are no such shelves! Obviously, this is not beneficial for them and the current will not flow in this direction.

Thus, any diode can act as a kind of valve for electricity to flow through it in one direction but not in the other. It is this property of diodes that has made it possible to use them as the basis for computer technology - any computer, smartphone, laptop or tablet contains a processor based on millions of microscopic diodes.

LEDs, of course, have another application - in lighting and display. The very fact of the appearance of light is associated with a special selection of semiconductor materials that make up the diode. In some cases, the same transition of electrons from the cathode to anode vacancies is accompanied by the release of light. In the case of different semiconductors, luminescence of different colors occurs. Important advantages of diodes compared to other electric light sources are their safety and high efficiency - the degree of conversion of electrical energy into light.

It happens that you find yourself in a difficult life situation when you urgently need a source of energy. For example, you need to charge your mobile phone, turn on the radio, and so on. Basic knowledge of physics and chemistry will allow you to find a way out of such situations. For many, it will be interesting to know that you can “power” the radio or charge your mobile phone from an apple or lemon.

For these purposes you will need:
- steel contact (nail, paper clip, piece of steel wire, steel coin, and so on...);
- copper contact (copper coin, piece of copper wire, any copper plate, etc.);
- lemon, and if you use an apple, you need to choose one that is as sour as possible;
- two wires for connecting to the “battery”.

Procedure:

Stage 1. Looking for a suitable “energy source”
The easiest way is to find an apple when you are in a country house, a village, or simply lost in the forest. The best option would be a sour apple, since acid is a key component in the operation of the battery. If there is lemon, then this is the most suitable option. You can also use oranges, kiwis and other similar fruits.

Stage 2. Establishing contacts
You need to insert contacts into a lemon or an apple; first you need to clean them thoroughly with sandpaper, a file, or rub them on a stone. The contacts are inserted at a distance of 2-3 centimeters from each other. The wider and longer the inserted electrodes, the more voltage the battery will produce. If coins act as contacts, then they must be inserted in parallel.

Stage 3. Connect the battery
Now all that remains is to connect the two wires to the installed contacts. You can simply carefully stick them into a lemon or apple along with the contacts. That's all, the battery is ready for use. There will be a plus on the copper electrode, and a minus on the steel electrode. The voltage will depend on the area of ​​the electrodes and the acidity of the apple or lemon.

One such battery is capable of delivering about 0.5-0.8 Volts. In order for a simple receiver to work or a mobile phone to charge, a voltage of at least 3-5 Volts is required. To obtain such power, you need to make several of these “batteries” and connect them in series. In our case, to get 3 Volts you will need about 5-6 of these “batteries”.

Stage 4. Charge the lemons
An interesting fact is that the “batteries” created in this way can be charged. For these purposes, you can use a mobile phone charger. The author decided to use a Krona battery for these purposes.

The red positive wire is connected to the copper electrode, and the black negative wire to the steel electrode. After charging, a voltage of 1-1.3 Volts will appear on the “lemon” contacts.

For lovers of all kinds of experiments and experiments, we offer an unusual idea - try to build a primitive battery from sour lemons with your own hands. We spend a lot of money on batteries, accumulators to power phones, watches, toys, without thinking at all that we are surrounded by a lot of inexpensive energy sources, from which we can assemble an economical and simple galvanic cell with our own hands at any time. We can’t even imagine how many interesting things surround us!

To carry out the experiment we will need, as I mentioned above, lemons (8 pieces), 9 thin wires with clamps, 8 small pieces of copper wire and the same number of galvanized nails, a watch with a battery, and, of course, a voltmeter to test the capabilities ( voltage) of the battery we built.

Having lightly kneaded the lemons in our hands, we stick a piece of copper wire and one galvanized nail into each of them. We take a watch, remove the battery from it, and using wires we create an electrical circuit, like in the drawing. We connect the free ends of the wires from the first and eighth lemon to the clock in the places where the battery was previously located, creating a closed circuit. At the end of the experiment we will see how the clock goes. By connecting the ends of the wires to a voltmeter, we can observe a voltage of 0.49 V.

It's easy to explain how our fruit battery works. When copper and zinc come into contact with citric acid, a chemical reaction occurs, as a result of which copper becomes positively charged and zinc becomes negatively charged. When a closed circuit is created using copper wire and small galvanized nails, an electric current begins to operate. Zinc (source of electrons) is the negative pole fruit battery, copper – positive. The voltage in the batteries is related to the ability of the zinc and copper to give up electrons. The electric current depends on the number of electrons released during the chemical reaction.

If you don’t have lemons at home, you can use any other citrus fruits, kiwi, bananas, apples, pears, potatoes, tomatoes, cucumbers, and onions as the main material for the experiment. These vegetables and fruits can also work as a battery, although their voltage will be slightly different from the lemon current source. A pear will give the highest voltage, and a kiwi will give the lowest. The electrical characteristics of the batteries being created are affected by the acidity of the products used. By connecting several fruit batteries in series, we will achieve an increase in voltage proportional to the number of fruits used.

The copper and zinc pair can be replaced with other components, for example, copper and aluminum, aluminum and zinc. True, in the latter case the battery will turn out to be somewhat weaker than the “original” lemon one.

The experiment described above is direct confirmation that people can freely use natural, renewable materials to meet their energy needs. A number of companies on an industrial scale have already begun to create unusual batteries using processed products from bananas and orange peels. The Sony company not long ago presented to the public a battery in which fruit juice was used instead of electrolyte. By filling the battery with 8 ml of juice, you can power small portable electronics for one hour. Scientists from the UK have created a similar version of the battery for a low-power computer with an IPte1 386 processor. It has been experimentally proven that 12 potatoes can become a full-fledged source of energy for a computer for 12 days.

Juicy fruits, new potatoes and other food products can serve as food not only for people, but also for electrical appliances. To generate electricity from them, you will need a galvanized nail or screw (that is, almost any nail or screw) and a piece of copper wire. To detect the presence of electricity, we will need a household multimeter, and an LED lamp or even a fan powered by batteries will help us more clearly demonstrate success.

Mash the lemon in your hands to break down the internal membranes, but do not damage the peel. Insert a nail (screw) and copper wire so that the electrodes are located as close to each other as possible, but do not touch. The closer the electrodes are, the less likely it is that they will be separated by a partition inside the fruit. In turn, the better the ion exchange between the electrodes inside the battery, the greater its power.

The essence of the experiment is to place the copper and zinc electrodes in an acidic environment, be it lemon or a bath of vinegar. The nail will serve as our negative electrode, or anode. We will assign the copper wire as the positive electrode, or cathode.

In an acidic environment, an oxidation reaction occurs on the surface of the anode, during which free electrons are released. Each zinc atom loses two electrons. Copper is a strong oxidizing agent and can attract electrons released by zinc. If you close an electrical circuit (connect a light bulb or multimeter to an improvised battery), electrons will flow from the anode to the cathode through it, that is, electricity will appear in the circuit.

Potatoes are naturally an excellent casing and electrolyte for a galvanic cell. Potatoes consistently gave us a voltage of more than 0.5 V per cell, while lemon showed a result of around 0.4 V. The champion in voltage is vinegar: 0.8 V per cell. To obtain higher voltage, connect the elements in series. To power more powerful consumers (fan) - in parallel.

On the surface of the cathode, that is, a negatively charged electrode, a reduction reaction occurs: cations (positively charged ions) of hydrogen contained in the acid receive the missing electrons and turn into hydrogen, which comes out in the form of bubbles. A concentration of acid anions (negatively charged ions) occurs near the cathode, and zinc cations occur near the anode. To balance the charges in the electrolyte, it is necessary to ensure ion exchange between the electrodes inside the battery.

Increased soil acidity is a problem for agronomists, but a joy for electrical engineers. The content of hydrogen and aluminum ions in the soil allows you to literally stick two sticks (as usual, zinc and copper) into the pot and generate electricity. Our result is 0.2 V. To improve the result, the soil should be watered.

It is important to understand: electricity is not generated from lemons or potatoes. This is not at all the energy of chemical bonds in organic molecules that is absorbed by our body as a result of food consumption. Electricity arises from chemical reactions involving zinc, copper and acid, and in our battery it is the nail that serves as the consumable material.