Chemical guard. Fun chemistry experience at home

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Entertaining experiments in chemistry

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We called this experiment a chemical watchman, and its more strict name is a chemotron sensor. Chemotronics is a new branch of science, it arose at the intersection of electronics and chemistry. Unlike electronics, it studies processes in a liquid where ions move. Since ions are much heavier than electrons, chemotronic processes are slower. But speed is not always the most important thing. Chemotronic devices are very reliable, they are already finding many applications.

Of course, real chemotronic devices are complex. And yet you can make a model of one such device - a sensor. First of all, it is curious to see how chemotrons work. And in addition, this sensor will surely serve you in good stead.

First, make a cylindrical body. It would be best to carve it from plexiglass on a lathe, but this is not necessary; the body can also be glued from separate Plexiglas plates, in which case it will be rectangular. The approximate diameter of the round case is 40 mm, and the height is about 20 mm. Two cavities about 5 mm deep and 30 mm in diameter must be machined from the ends of the cylinder, so that a thick-walled bridge remains between them. Directly under the jumper, drill a horizontal hole with a diameter of 2-3 mm for pouring electrolyte and pick up a tight plug to this hole. Then, on the opposite side of the case, drill three more holes for the electrodes, one under the other, with a diameter slightly larger than a millimeter. The central electrode must be in the jumper, the upper and lower - in the corresponding cavities.

As electrodes, take thick stylus for collet pencils. Those places where the slates come out of the body must be sealed with some kind of glue. When the glue dries, drill vertically a very thin through hole with a diameter of no more than 0,5 mm in the jumper. When choosing a place for it, keep in mind that this hole must pass through the middle lead electrode.

The device is almost ready. It remains only to glue to it from above and below along a thin membrane from that æe plexiglass, only of a small thickness (0,3-0,5 mm). Glue only the bottom membrane for now.

Now about the electrolyte. Dissolve 20-30 g of potassium iodide in half a glass of water, and then, slightly warming the solution, add about 1 g of iodine. Through the side, wider opening, pour this electrolyte into the sensor, into the lower cavity, making sure that no air bubbles remain. The easiest way to carry out this operation is with a medical syringe. When the upper cavity is also filled, glue the second membrane and finally seal the case by inserting a pre-prepared plug into the inlet and carefully filling it with glue.

The chemotronic sensor will be powered by a flashlight battery. Connect the upper and lower electrodes located in the cavity to the positive pole of the battery, the middle one to the negative. It is desirable to include a rheostat in the circuit, as well as a voltmeter and a microammeter, which, as you already know, can be replaced with a tester.

Using a rheostat (or resistances), set the voltage to approximately 0,8-0,9 V. A microammeter connected to the central electrode circuit will show a current of 200-300 μA. Leave the chain closed for ten to fifteen hours. The current will gradually drop to 10-20 µA, which is what is required. The sensor is now ready for use.

The easiest way to check how it works is to blow on one of the membranes or touch it with the tip of a needle. At the same instant, the microammeter needle will sharply deviate to the right. The movement of the membrane is invisible to the eye, but the sensor responded to it immediately.

Let's explain why this happens. The current strength depends on how much iodine is near the negative cathode electrode. Under the action of a direct current, pod at the cathode is restored, accepting electrons, and at the anode it is again formed from ions. Therefore, iodine is, as it were, gradually pumped from the cathode to the anode. After charging the sensor, the current gradually drops, because less and less iodine remains at the negative electrode. But as soon as you slightly, even with a weak touch, shifted the membrane, an additional, albeit very small, portion of iodine molecules enters the cathode; the sensor instantly reacts to this: the current increases.

Such chemotronic devices are extremely sensitive; carefully crafted, they can sometimes react to literally a few molecules. Their sensitivity is used in practice - when the signal is weak and difficult to register in other ways. Such chemotronic devices are used, for example, in medical research, in technology - to count small parts moving on a conveyor.

Is it possible to somehow use such a sensor at home or at school? Of course you can. Why not turn it into a device that will alert you when a guest arrives? To do this, it is enough to put the sensor in the doorway of the apartment, and it will respond as soon as the guest touches the door.

But, of course, one such sensor, by itself, is not very convenient for this purpose: you have to look at the microammeter all the time and wait until its arrow deviates. However, an alarm system can be adapted to the sensor - a bell or an electric lamp. How to do this - figure it out yourself or consult a physics teacher.

By the way, such a chemotronic "watchman" can be used to protect important objects, such as banks. Of course, in this case, the sensor is by no means hospitable - it warns of danger.

Author: Olgin O.M.

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