Just two drops of glycerin - and potassium permanganate changes its color!
Complexity:
Danger:
Do this experiment at home
Why does the solution turn blue at first?
If you watch the chameleon closely, you will notice that within a few seconds of adding glycerin to the solution, it will turn blue. The blue color is formed by mixing violet (from MnO 4 - permanganate) and green (from MnO 4 2- manganate) solutions. However, it turns green quite quickly - there is less and less MnO 4 - and more MnO 4 2- in the solution.
Addition
Scientists were able to discover in what form manganese is capable of turning a solution blue. This occurs when it forms the hypomanganate ion MnO 4 3-. Here manganese is in the +5 oxidation state (Mn +5). However, MnO 4 3- is very unstable, and special conditions are required to obtain it, so it cannot be seen in our experience.
What happens to glycerin in our experiment?
Glycerol interacts with potassium permanganate, giving it its electrons. Glycerol was taken in our reaction in large excess (about 10 times more than potassium permanganate KMnO4). Under the conditions of our reaction, glycerol itself turns into glyceraldehyde, and then into glyceric acid.
Addition
As we have already found out, glycerol C 3 H 5 (OH) 3 is oxidized by potassium permanganate. Glycerol is a very complex organic molecule, and therefore reactions involving it are often complex. The oxidation of glycerol is a complex reaction during which many different substances are formed. Many of them exist for only a short time and are transformed into others, and some can be found in solution even after the reaction is complete. This situation is typical for all organic chemistry as a whole. Typically, those substances that are produced the most as a result of a chemical reaction are called the main products, and the rest are by-products.
In our case, the main product of glycerol oxidation with potassium permanganate is glyceric acid.
Why do we add calcium hydroxide Ca(OH) 2 to the KMnO 4 solution?
In an aqueous solution, calcium hydroxide Ca(OH) 2 breaks down into three charged particles (ions):
Ca(OH) 2 → Ca 2+ (solution) + 2OH - .
In transport, a store, a cafe or in a school classroom - everywhere we are surrounded by different people. And we behave differently in such places. Even if we do the same thing - for example, read a book. Surrounded by different people, we do it a little differently: somewhere slower, somewhere faster, sometimes we remember what we read well, and other times we can’t remember even a line the next day. Likewise, potassium permanganate, surrounded by OH ions, behaves in a special way. It takes electrons from glycerol “more gently”, without rushing anywhere. This is why we can observe a change in the color of the chameleon.
Addition
What happens if you don’t add a Ca(OH) 2 solution?
When an excess of OH - ions is present in a solution, such a solution is called alkaline (or is said to have an alkaline reaction). If, on the contrary, there is an excess of H + ions in the solution, such a solution is called acidic. Why "on the contrary"? Because together the OH - and H + ions form the water molecule H 2 O. But if the H + and OH - ions are present equally (that is, we actually have water), the solution is called neutral.
In an acidic solution, the active oxidizing agent KMnO 4 becomes extremely untrained, even rude. It very quickly takes electrons away from glycerol (as many as 5 at a time!), and manganese turns from Mn^+7 (in permanganate MnO 4 -) to Mn 2+:
MnO 4 - + 5e - → Mn 2+
The latter (Mn 2+) does not give the water any color. Therefore, in an acidic solution, potassium permanganate will discolor very quickly, and a chameleon will not turn out.
A similar situation will occur in the case of a neutral solution of potassium permanganate. Only we will not “lose” all the colors of the chameleon, as in an acidic solution, but only two - the green manganate MnO 4 2 will not be obtained, which means the blue color will also disappear.
Is it possible to make a chameleon using anything other than KMnO 4?
Can! A chromium (Cr) chameleon will have the following color:
orange (dichromate Cr 2 O 7 2-) → green (Cr 3+) → blue (Cr 2+).
Another chameleon - from vanadium (V):
yellow (VO 3+) → blue (VO 2+) → green (V 3+) → purple (V 2+).
It’s just much more difficult to make solutions of chromium or vanadium compounds change their color as beautifully as happens in the case of manganese (potassium permanganate). In addition, you will have to constantly add new substances to the mixture. Therefore, a real chameleon - one that will change its color “on its own” - can only be obtained from potassium permanganate.
Addition
Manganese Mn, like chromium Cr and vanadium V, are transition metals - a large group of chemical elements that have a whole range of interesting properties. One of the features of transition metals is the bright and varied color of compounds and their solutions.
For example, it is easy to obtain a chemical rainbow from solutions of transition metal compounds:
Every Hunter Wants to Know Where the Pheasant Sits:
Red (iron (III) thiocyanate Fe(SCN) 3), iron Fe;
Orange (dichromate Cr 2 O 7 2-), chromium Cr;
Yellow (VO 3+), vanadium V;
Green (nickel nitrate, Ni(NO 3) 2), nickel Ni;
Blue (copper sulfate, CuSO 4), copper Cu;
Blue (tetrachlorocobaltate, 2-), cobalt Co;
Violet (permanganate MnO 4 -), manganese Mn.
Development of the experiment
How to change the chameleon further?
Is it possible to reverse the reaction and get a purple solution again?
Some chemical reactions can occur in one direction or in the opposite direction. Such reactions are called reversible and, compared to the total number of chemical reactions, not so many of them are known. You can reverse the reaction by creating special conditions (for example, high heating of the reaction mixture) or by adding some new reagent. The oxidation of glycerol with potassium permanganate KMnO 4 is not a reaction of this type. Moreover, within the framework of our experiment, it is impossible to reverse this reaction. Therefore, we will not be able to force the chameleon to change its color in the reverse order.
Addition
Let's see if there is a way to convert our chameleon?
First a simple question: can oxidized glycerol (glyceric acid) turn manganese dioxide MnO 2 back into violet potassium permanganate KMnO 4? No, it can't. Even if we help him a lot (for example, heat the solution). And all because KMnO 4 is a strong oxidizing agent (we discussed this a little higher), while glyceric acid has weak oxidizing properties. It is incredibly difficult for a weak oxidizing agent to oppose anything to a strong one!
Is it possible to convert MnO 2 back to KMnO 4 using other reagents? Yes, you can. But for this you will have to work in a real chemical laboratory! One of the laboratory methods for producing KMnO 4 is the interaction of MnO 2 with chlorine Cl 2 in the presence of excess potassium hydroxide KOH:
2MnO 2 + 3Cl 2 + 8KOH → 2KMnO 4 + 6KCl + 4 H 2 O
You cannot carry out such a reaction at home - it is both difficult (you will need special equipment) and unsafe. And she herself will have little in common with the bright and beautiful chameleon from our experience.
Scheele Volcano - classic version
Scheele Volcano is one of the simplest and most spectacular experiences. A couple of decades ago, when potassium permanganate (“potassium permanganate”) and glycerin were sold in any pharmacy, this experiment could be done by every schoolchild - even those not particularly inclined to conduct chemical experiments. Nowadays, when chemistry and the chemical industry are virtually outlawed, getting potassium permanganate is very problematic, but in this article we will not touch on these outrageous aspects of our reality.
So, the experimental design is extremely simple: a pile of potassium permanganate (usually a few grams) is poured onto a refractory surface. A depression is made in the slide - a “volcano crater” and a few drops of glycerin are dropped into it. After some time (seconds, sometimes minutes) a “volcanic eruption” begins. Yellow, white and blue flames appear, sparks fly in all directions.
Usually, carrying out the experiment does not cause difficulties, but there are still some peculiarities. When the author first decided to conduct this experiment (being no longer a young chemist), he was disappointed: glycerin never wanted to catch fire. The glycerin looked thick, it obviously did not contain significant amounts of water, but the experiment did not work. I asked my colleagues: it turns out that they did not have such problems. I took another glycerin - the result was not long in coming: from contact with permanganate, the glycerin quickly caught fire. Most likely, the “bad” glycerin contained an admixture of oil (the liquid was greasy to the touch).
However, the more common reason why the experiment may not work (or work, but poorly) is different: glycerin should be anhydrous or at least contain less water.
A few years after the events described, we decided to repeat the experiment. The glycerin that came to hand was a bit “thin”: it clearly contained a lot of water. Permanganate was taken in the form of large crystals. Ignition occurred, but the “volcanic eruption” had to wait several minutes. Before the mixture ignited, the liquid boiled, producing white vapor as water and glycerin evaporated.
It is very easy to remove water from glycerin: you need to carefully heat it in an open vessel. First, the liquid boils - water evaporates from it. When the boiling stops and thick white vapor begins to form, the procedure is complete: almost all the water has evaporated. Contact with a flame may cause glycerin vapor to ignite. If this happens, turn off the burner and cover the opening of the vessel to stop air from reaching the glycerin (a piece of plywood, cardboard or thick paper is suitable for this purpose).
Don’t even think about pouring water into burning glycerin! The water will immediately evaporate, carrying with it droplets of glycerin, which will immediately burst into flames. The effect will probably be less than adding water to hot oil, but you can still get seriously hurt.
Using chemical reagents, you can make a fire without matches or other means of ignition. For example, it is relatively easy to make fire from sugar and potassium permanganate, potassium permanganate and glycerin - substances that are often found in a tourist first aid kit.
Today in Russia and Ukraine potassium permanganate is prohibited for sale without a prescription and therefore buying it for tourism purposes is more difficult, but still possible.
There are also other ways to produce chemical fire using various substances, which are simply useful to know about. For example:
- Potassium permanganate + sulfuric acid + ethanol. To start a fire using potassium permanganate, drop a few drops of concentrated sulfuric acid onto dry potassium permanganate powder. If you now put cotton wool soaked in ethyl alcohol into the mixture, the cotton wool will catch fire.
- Chromium trioxide + ethanol. A little chromium trioxide is poured onto cotton wool moistened with ethyl alcohol. At the moment of contact of the reagents, the cotton wool ignites.
- Sodium or potassium + water. When one of these metals comes into contact with water, a violent reaction occurs with ignition.
- Potassium chlorate + sugar + sulfuric acid. To produce fire, powdered sugar is mixed with potassium chlorate, after which concentrated acid is dripped onto the resulting mixture. The moment the mixture comes into contact with sulfuric acid, a fire occurs.
- Aluminum + iodine. For this method, you will need to conduct a chemical experiment with crystalline iodine. It is mixed with aluminum powder and a little water is added to the finished mixture - after a short time the mixture lights up.
In fact, there are many more ways to start a fire using chemical reagents, but almost none of them are suitable for a tourist who finds himself in an emergency situation, because most of the reagents, not only on a hike, but also in a populated area, cannot always be bought.
Potassium chlorate ignites when in contact with sulfuric acid and sugar, but try buying it. Moreover, admit it: will you carry it in your backpack along with sulfuric acid?
It is even believed that fire can be started using hydrogen peroxide. This is not true, however: this reaction does not actually cause combustion, but can support it. So, if you add potassium peroxide to hydrogen peroxide, a rapid release of oxygen will begin. And in an oxygen environment, as is known, even a smoldering splinter instantly ignites.
In survival conditions, I don’t see any point in using hydrogen peroxide in this way: it will be more useful if it is used for its intended purpose, that is, for the purpose of disinfecting wounds and scratches.
I know of only a couple of chemical methods of starting a fire without matches and other devices for ignition, which can be implemented in the wild, for example, in a forest, with reagents that are generally available and found in a tourist’s first aid kit. These are methods using mixtures of potassium permanganate + glycerin and potassium permanganate + sugar.
These methods are based on the fact that potassium permanganate, when heated (in our case from friction), and sometimes at room temperature, actively interacts with various organic substances, for example, with the mentioned glycerin and sugar.
Starting a fire with potassium permanganate and glycerin
Potassium permanganate and glycerin can be stored in a travel first aid kit. Potassium permanganate is usually taken for the preparation of antiseptic solutions, and glycerin is used for various cosmetic and some other medical procedures.
Fire starting glycerin should be anhydrous or at least contain a minimal amount of water.
Note
Potassium permanganate (also known as potassium permanganate) in the Russian Federation and Ukraine was recognized as a precursor and included in the list of narcotic substances. However, it can still be purchased in some pharmacies, albeit in small quantities and at a considerable price.
In order to get fire using this method, you need to drop a few drops of glycerin onto potassium permanganate. After some time, the mixture will react, emitting smoke, and then ignite. It looks like this:
Safety precautions when using this method:
- Avoid contact of potassium permanganate with skin, mucous membranes (burns are possible) and clothing (stains may remain).
- Do not extinguish such a fire with water. The ingress of water causes the mixture to splash.
- Fire should be produced in this way in the open air, since overheating of glycerin promotes the release of acrolein, a toxic substance of the 1st hazard class. The same substance is released when fat burns during cooking.
Note
By the way, the negative effect of acrolein on the human body is also evidenced by the fact that during the First World War it was used as a chemical weapon.
Starting a fire with potassium permanganate and sugar
This method, in my opinion, is more universal for tourists than the previous one, since, unlike glycerin, most lovers of outdoor activities in the wild take sugar with them. Although in fact you can do without sugar at all, using only potassium permanganate, we will consider the most popular option.
Note
Potassium permanganate is often called manganese, although this is incorrect, since these are two different substances. The first is a dark purple-colored salt, and the second is a silver-white metal. Potassium permanganate is a more correct name for potassium permanganate.
The algorithm for obtaining fire in this way is as follows:
- Take flammable tinder, such as cotton wool or dry grass.
- A small stick is made from a dry but strong branch and pointed at the end.
- A small depression is cut out in a log or wooden plank along the diameter of the cross-section of the prepared stick.
- The tip of the stick is placed in the recess and rubbed in.
- Potassium permanganate is mixed with sugar in a ratio of 9:1 and placed in the recess.
- The mixture is pressed with a stick to the bottom of the recess, and tinder is placed above it along the perimeter.
- Rubbing a mixture of potassium permanganate and sugar produces a flash that causes the tinder to ignite. But, as already mentioned, the use of sugar in this method is not necessary: it is better to leave it for gastronomic purposes.
ATTENTION! It is unacceptable to prepare and store ready-made mixtures with potassium permanganate in advance: due to the strong oxidizing properties of potassium permanganate, such mixtures can spontaneously ignite or explode. Do not carry already mixed potassium permanganate and sugar in your backpack - such kindling can only be prepared immediately before starting a fire.
When using this method of starting a fire without matches, it should be remembered that during an outbreak, excess potassium permanganate can fly apart, getting on a person and his clothing.
If you only have potassium permanganate without sugar on hand, you can make a fire as shown in the video below:
In general, potassium permanganate is a necessary thing when camping, and not only for starting a fire. It can be used to disinfect water, to treat poisoning with certain alkaloids, to wash wounds and, as we can see, to make fire. Therefore, it makes sense to purchase potassium permanganate and carry it not only in the first aid kit, but also in the NAZ. For example, I carry a small amount of potassium permanganate in my cord bracelet: there it is sealed in a sealed flexible container and is located between the weaves of the cord.
Interesting video: 10 most common ways to create fire using chemical reactions:
