Some substances, participating in chemical reactions, have the ability to emit light. Every amateur chemist at least once made a luminous liquid. This article will discuss what luminol is, how to prepare it at home.
What is chemiluminescence?
Many reactions in chemistry proceed with the release of energy. In most experiments, energy is released as heat. With the interaction of alkalis and acids, the solutions heat up. There are cases when energy can manifest itself in the form of an electric current (experiments with galvanic cells). When reacting substances are burned, energy is converted into heat and light.
But there are reactions in which light is emitted, but no increase in temperature is observed. This phenomenon is called chemiluminescence. The most striking example is the cold glow of phosphorus. It should be noted that in most chemical reactions with the release of “cold light” organic compounds are oxidized . The oxidizing agents are usually oxygen or hydrogen peroxide.
In nature, there are many substances that can emit light. But most often the glow is very weak and can only be detected with the help of special equipment.
A relatively small group of organic and inorganic compounds is capable of bright and beautiful chemiluminescence. The following substances can be cited as examples: luminol, siloxene, lofin, lucEGenin and diphenyloxalate.
What is luminol?
Luminol was synthesized in Germany in 1902, but got its real name later. It is a white or light yellow crystals, readily soluble in polar organic solvents. In water, luminol is completely insoluble.
It is an organic substance capable of emitting light when combined with hydrogen peroxide or other oxidizing agents. In neutral and slightly acidic liquids, when illuminated with ultraviolet light, it fluoresces with a light blue light. In alkaline solutions (hydrogen peroxide), where the reaction proceeds in the presence of catalysts - phosphorus compounds, metal salts, hemin and hemoglobin - the glow is more saturated and bright.
The process consists of 2 stages. The acid is heated with hydrazine in a high boiling point organic solvent (3-ethylene glycol). As a result of condensation, a heterocyclic system of 5-nitrophthalylhydrazide is obtained. This compound is reduced with ammonium sulfide, resulting in the formation of luminol. With your own hands it can be obtained in laboratory conditions by synthesis from 3-nitro-phthalic acid.
Where are luminol used?
The substance in question reacts remarkably with iron, which is part of the hemoglobin of the blood. Therefore, it is widely used by forensic experts in identifying traces of blood and fingerprints left at the crime scene. Luminol is used by scientists in various biological studies to detect iron, copper and cyanides.
Where to buy luminol solution
The cost of luminol is quite high. You can search it on chemical forums, special bases or in pharmacies. If you do not know where to get luminol, then you can buy it at the Galavit pharmacy, which is available in tablets, ampoules and suppositories. The tablet contains 25 mg of luminol sodium. For 50 ml of a 1% solution, 20 tablets are needed (packaging). The tablets are ground into powder, and then water is added to it.
Luminous liquid with hydrogen peroxide
There are recipes for making luminous fluids from improvised products. But for the preparation of the solution, it is best to use luminol, because it gives an even and soft bluish light. Before starting work, be sure to protect exposed parts of the body with a thick cloth and wear gloves on your hands.
Let's prepare luminol at home according to the classic (first) recipe:
- Luminol - 2-3 grams.
- Water - 0.1 liters.
- A solution of hydrogen peroxide (3%) - 0.08 liters.
- Caustic Sodium - 0.01 liters.
- Copper sulfate - 3 grams.
- Dyes (chopped, brilliant green or any other).
- Glassware (flasks or jars).
Cooking process:
- Pour water into a glass container and add luminol. Thoroughly mix the crystals in water so that they dissolve as much as possible in it.
- We add hydrogen peroxide to the resulting solution.
- In the resulting composition, add copper sulfate. Sulfate can be replaced with iron chloride or blood salt.
- The most recent sodium hydroxide is added to the composition.
- In the room we turn off the light. The resulting composition should emit a bright blue glow. If a different color is needed, then add the desired fluorescent dye to the solution.
The second option:
- Luminol solution (3%) - 5 ml.
- Hydroperite (3%) - 10 ml.
- Washing powder with water - 20 ml.
- Potassium permanganate.
- Any glass jar or jar.
Work Stages:
- Pour solutions of luminol, washing powder and hydrogen peroxide into the container.
- Gently rub several crystals of potassium permanganate and add it to the overall composition.
- To see what luminol is and how it will manifest its properties, turn off the light in the room. The liquid will emit a beautiful glow. If the solution is periodically mixed, then sparkling foam will appear on its surface.
Preparation of dimethyl sulfoxide solution
A more interesting option would be the oxidation of luminol with atmospheric oxygen in a dimexide environment. Glow occurs at the interface between air and water.
To prepare the composition, we need:
- Luminol - 0.15 grams.
- Dimexide (dimethyl sulfoxide) - 30 ml.
- Dry alkali - 35 grams.
- Any fluorescent dye.
- High glassware.
Stages:
- Thoroughly mix dimexide, luminol and alkali in a flask.
- Close the flask tightly with a lid.
- In the room we turn off the light.
- Shake the flask until a bluish glow. To change the color, add a fluorescent dye.
- If the glow has lost its brightness, then you can open the tank. When air enters the flask, the solution again becomes bright and saturated.
Cooking Tips
It is not recommended to add a lot of alkali to the solution, because it is very poorly soluble and turns the liquid into a thick porridge. A suspension of luminol, dimexide and alkali can be stored for a rather long time. When an oxidizing agent is added, the glow will be uniform. Its duration depends on the amount of hydroperite and luminol and can reach 40 minutes. But from an excess of luminol, the glow becomes weaker.
It should be noted that the brightness and duration of the glow will also depend on the concentration of luminol. Highly diluted solutions give a faint but lasting glow. A large concentration of the substance forms a strong brightness of the entire solution. The color of the glow can vary from blue to green. In more saturated formulations containing a high concentration of blood salt, a green glow is obtained.
Can luminol be replaced?
There are situations when it is necessary to prepare a luminous liquid without luminol. To do this, take boric acid and a few drops of fluorescein. These substances must be mixed and heated on a metal plate. The liquid will glow in the dark for about a minute.
To understand what luminol is, it is better to try to get it yourself. As they say, it is better to see once than hear a hundred times. But do not forget that any experiments involve interaction with caustic and harmful substances. Therefore, safety precautions must be observed.