Dissolving (mixing liquids and liquids with solids) is the main step of solution preparation. The most important of all physic-chemical features of substances is the ability to dissolve in water or other liquids – solubility. It can be determined by the concentration of the saturated solution under defined circumstances.
It can be characterized by the same means as concentration (in the percentage of the dissolved substance or moles per one liter of solution). However, the most usual characterizer is the number of grams of the substance dissolved in 100 ml of dissolvent under defined temperature rates.
A great role in the mixture of liquids and preparation of solutions is played by the nature of the dissolved substance and a dissolvent. The same substance has different rates of solubility in different kinds of dissolvent and vice versa – different substances mix differently with the same dissolvent.
From a practical side, the essential rule which let’s determine overall regulations of solubility is known as an ancient principle “the similar is dissolved in similar” known by alchemists.
In modern time the essence of this solubility rule is determined as the approach to solubility as the result of homogeneous molecular contents of a substance and the dissolvent. This structural similarity allows the possibility of a spontaneous molecular mixture. Also, it determines the similarity of intermolecular forces in a solution.
The solubility rule comes to the fact that dissolvent substances, which consist of nonpolar molecules mix well with nonpolar substances. The substances with polar molecules dissolve much worse.
At last, substances with the highest polarity of molecules cannot be mixed with such vehicles. And vice versa, the vehicles with a good polarity of molecules mix good with polar substances and bad with unipolar ones.
The simplest mixture of liquids happens when there is no chemical reaction between molecules of dissolved substances when the contents of these substances are similar. In this case, the environment of the solution does not differ from the environment of the pure substance. When the size of molecules is equal, they penetrate the layers of one another with the same speed and their properties do not change dramatically.
In this case, the mixture of liquids is determined by diffusion. The appearance of the solution is not accompanied by temperature effects and volume changes because there is no energy spending.
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