What exactly does the principle of similarity and compatibility refer to?

Similar compatibility means that molecules with the same structure are easily soluble in each other

Haiyou: “"Similar" means that the solute and the solvent are structurally similar. ； “"Miscible" means that the solute and the solvent are mutually soluble in each other. For example, there are strong hydrogen bonds between water molecules. Water molecules can not only provide hydrogen atoms for the formation of hydrogen bonds, but also have lone pairs of electrons on the oxygen atoms that can accept hydrogen atoms provided by other molecules. Hydrogen bonds are the main binding force between water molecules. Therefore, any solute molecule that can provide hydrogen or accept hydrogen to form a hydrogen bond is "structurally similar" to water. For example, ROH (alcohol), RCOOH (carboxylic acid), R2C=O (same), RCONH2 (amide), etc., can be combined with water through hydrogen bonds and have considerable solubility in water. Of course, the structure and size of the R group in the above substances also affect the solubility in water. Such as alcohol: R—OH, as the R group increases, the non-polar part of the molecule increases, which increases the structural difference from water (polar molecule), so the solubility in water gradually decreases. For gases and solid solutes, "like dissolves like" also applies. For a type of gas with a similar structure, the higher the boiling point, the greater the intermolecular force, and the closer it is to a liquid, so the solubility in the liquid is also greater. For example, the boiling point of O2 (90K) is higher than the boiling point of H2 (20K), so the solubility of O2 in water is greater than the solubility of H2. For a type of solid solute with similar structure, the lower the melting point, the smaller the intermolecular force, and the closer it is to a liquid, so the solubility in the liquid is greater.

The principle of similar compatibility is based on the molecular polarity of mutually soluble substances, such as polar molecules soluble in polar molecules.

The so-called similarity refers to the structure and the interaction between them. Needless to say, compatibility. In short, it is more difficult for a person with low quality like me to get along with people with high education, because I like to drink and goof off, while others like to be fulfilled and struggle. The interaction between molecules is similar to this. The good relationship between water and ethanol is entirely due to their similarities in hydroxyl groups, hydrogen bonds, etc. Regarding the specific issue of the original poster, we should first look at which one is more similar. In addition, we should also look at the subsequent separation costs, etc.

It mainly depends on whether the molecular structure is polar or non-polar. Polar molecules can be dissolved when mixed with polar molecules, while non-polar molecules are generally insoluble when mixed with polar molecules.