Why can alcohol kill bacteria and disinfect? ​​Why is it not the higher the concentration, the better? Can it be mixed with 84?

Alcohol is the most common disinfectant, especially during epidemics. Alcohol is a common reagent in every household. Alcohol is ethanol, the main active ingredient in the wine we usually drink. So can this drink really kill bacteria? The answer is yes.

Alcohol is ethanol, and its chemical formula is C2H5OH. As can be seen from the chemical formula, it is composed of two carbon atoms, five hydrogen atoms and one hydroxyl group. There are two main reasons why alcohol can kill bacteria and disinfect. One is that alcohol can cause cell dehydration, and the other is that alcohol can denature proteins. We know that all bacteria are single-cell organisms, while viruses are a mass of genetic material, not even cells. So how does alcohol kill bacteria and viruses respectively? First of all, the process of killing bacteria is relatively complicated.

As single-celled organisms, bacteria have a cell membrane, within which are genetic material and water. Water is a small molecule that can penetrate the cell membrane and enter and exit freely.

So what determines whether water enters the cell or goes out of the cell? It is the difference in liquid concentration. According to osmosis, water always flows to areas with high concentrations. So when the cell is surrounded by alcohol, the liquid concentration outside the cell is significantly higher than that inside, which will cause the water inside the cell to flow out of the body, and the cell will die of dehydration. If the bacteria do not die from dehydration, it does not matter, because alcohol will penetrate into the cell through the cell membrane, causing the protein inside the cell to denature. The denatured protein loses its function, and the bacteria can no longer survive.

Compared to bacteria, viruses are actually more fragile. They are just a group of genetic material wrapped in protein, and alcohol can cause protein denaturation, so most viruses can be easily killed.

Some viruses are more tenacious, such as the COVID-19 virus, which is wrapped in a protective film on the outside of its body, which greatly improves its own survival ability. However, this film is still powerless in the face of alcohol, because this protective film is essentially a phospholipid membrane, which is insoluble in water but soluble in alcohol, so alcohol can also kill this tenacious virus effortlessly. However, although alcohol has a good killing effect on bacteria and viruses, in actual use, the higher the concentration, the better. If you use 100% alcohol to improve the sterilization effect, the effect is not ideal.

Why does the sterilization effect of 100% alcohol become weaker?

Alcohol can cause protein denaturation. The higher the concentration, the faster the protein denaturation. So when cells come into contact with 100% alcohol, the cell membrane denatures instantly. The denatured cell membrane loses its function. The water in the cell can no longer seep out of the cell, and alcohol can no longer enter the cell, and it cannot kill it. This is why we often say that 75% alcohol has the best sterilization and disinfection effect. When using alcohol, in addition to paying attention to the concentration, you must also pay attention to the way it is used. Wipe it instead of spraying it, because alcohol is very flammable. Imagine if you have just disinfected the whole house with a spray, and then someone lights a cigarette, the consequences will be disastrous.

In addition to alcohol, another disinfectant we often use is 84 disinfectant. In order to enhance the effect, some people will use alcohol and 84 disinfectant to wipe and disinfect the room or items one after another. Some people will directly mix the two liquids and use them, which is very undesirable.

84 disinfectant is an easy-to-use and cheap disinfectant. The reason why it is cheap is that the preparation process is very simple, and the raw material used is just salt water. When salt water is electrified, chlorine, hydrogen and sodium hydroxide are generated. Then, the chlorine generated by the reaction is mixed into the sodium hydroxide, and salt water and sodium hypochlorite are generated again. At this point, the preparation of 84 disinfectant is completed, which means that 84 disinfectant is actually sodium hypochlorite. Sodium hypochlorite is a strong oxidant, so it can effectively kill bacteria and viruses.

Although both 84 disinfectant and alcohol can kill bacteria and disinfect, their ingredients and principles are completely different. So some people think that mixing the two can kill bacteria and disinfect more effectively, but the result is just the opposite.

Alcohol is C2H5OH, and 84 disinfectant is sodium hypochlorite, which is NaClO. When the two are mixed, NaCl+H2O+CH3CHO will be generated, which is salt water and triacetaldehyde. Acetaldehyde is a carcinogen, flammable and volatile, but it has no bactericidal effect, and salt water has even less bactericidal effect. Therefore, mixing alcohol and 84 disinfectant to wipe the room is actually equivalent to wiping the room with salt water, which basically has no bactericidal effect. In fact, whether it is alcohol or 84 disinfectant, as long as it is used properly, it can perfectly remove bacteria and viruses in the room, and there is no need to use it with other disinfection products.

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