Chemical Engineering in Daily Life - Question 3 - Standard answers available
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This post was last edited by yjqin1 on 2015-8-20 at 18:02. Back in junior high school (in 1976), it was discovered that when crushed table salt was added to water drawn from a deep well, bubbles would form and the water would appear dirty. In the 1990s, I went abroad and led a simple life; of course, I had to deal with things like oil, salt, soy sauce, vinegar, and tea. When I added fine powder of refined salt purchased from foreign supermarkets to mineral water, these two phenomena still persisted. I started to think about why. Dear readers, why are there bubbles? Why does water appear dirty? This involves two physicochemical phenomena.
Why not the porous water absorption of salt crystals? I don’t understand the rest.
Does table salt provide vaporization centers, just like zeolites?
The dissolution of salt increases the concentration of substances in the water, and any undissolved salt or impurities present make the water appear cloudy.
This post was last edited by yjqin1 on 2015-8-20 at 19:32. Standard answer: There is a chemical phenomenon known as the salting-out effect, whereby the addition of a solute (usually an inorganic salt) to water can reduce the solubility of another solute. Such a solute can be a volatile substance, or even things like nitrogen, oxygen, carbon dioxide, air, etc. In ordinary water, when in contact with air, the partial pressure of air in the water is close to one atmosphere, or slightly less than one atmosphere. The above is Background Knowledge 1. Background Knowledge 2: There is another phenomenon called foam separation, which is an application of a surface phenomenon discussed in physical chemistry. If there are some impurities with low surface tension in the aqueous solution, they adsorb at the water-air interface; the polar groups in their molecules remain in the water, while the non-polar groups end up at the air-water interface. If there is movement at the air-water interface, these low surface activity substances will move along with the interface. For example, air bubbles rise due to buoyancy, and substances with low surface tension also rise. When salt dissolves and increases the salt concentration in the surrounding water, a salting-out effect occurs; this leads to supersaturation of air in the water that was previously saturated with air, resulting in the formation of bubbles. Because the salt particles are very small, numerous tiny bubbles are formed, which in turn leads to a foaming separation effect. Water contains more or less some organic substances, such as humic acids; the concentration of these impurities is very low, for example, <1 mg/L. However, due to the magnifying effect caused by the bubbles, they remain on the surface of the water temporarily and appear quite dirty. I only came to understand this principle in recent years.