Chemical Engineering in Daily Life – Question 28: Why doesn’t salt become damp during the hot summer days? Standard answer already exists
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This post was last edited by yjqin1 on 2015-9-10 at 20:59. The large-grained salt that used to be bought for use at home (crushed for cooking, or added directly when making pickles) would become damp during the hot summer months, that is, its surface would get wet； And the ground salt powder also clumps together during the hot summer days. Salt (in fine powder form) bought from supermarkets these days doesn’t exhibit such behavior; even when spread out on a plate, it doesn’t absorb moisture or clump together. Why?
The tobacco in our household gets damp; it doesn’t necessarily form clumps, but it absorbs moisture.
Presumably, the salt in your household is sold as smuggled salt. There are many fake salts these days. 80% of the salt in Baodi, Tianjin, is fake. Some time ago, reports indicated the discovery of over 100,000 tons of fake salt. It’s possible that (not necessarily) a certain chemical plant evaporates wastewater and then sells the resulting solid waste salts to unscrupulous merchants; this is even worse than gutter oil. Waste salt cannot be used as raw material in chlor-alkali plants; small soda ash plants have all disappeared, and large soda ash plants do not purchase waste salt. Let’s do the math: the waste salt produced by multi-effect evaporation and MVR processes ends up affecting our health, unless it is used in cement production, landfilled, illegally discharged, or dumped into the sea. Matter is indestructible!
Does coarse salt contain impurities? . . . . . . .
The salt I bought doesn’t absorb much moisture, but after some time (more than a month), there is still a little moisture present; however, it doesn’t form clumps. Why is that?
Low relative humidity, and what else? . . . .
It seems you don’t read the instructions on the packaging of table salt
When coarse salt becomes damp, is it because the salt did not crystallize properly during the crystallization process, resulting in many voids that allow it to absorb moisture from the air?； After being ground, the adsorption pores are destroyed, resulting in very low adsorption capacity.
Coarse salt absorbs moisture from the air and becomes damp, a process known as hygroscopicity. But it isn’t entirely caused by sodium chloride; it is mainly caused by other impurities such as magnesium chloride and potassium chloride, especially magnesium chloride. Modern table salt contains very little magnesium chloride, so it hardly absorbs moisture.
Ferrous **potassium, an anti-caking agent. Its appearance is that of light yellow monoclinic crystal particles or crystalline powder; its relative density is 1.853 at 17°C. It is odorless with a salty taste. It remains stable in air; when heated to 70°C, it loses its crystalline water and turns white. At 100°C, it forms a white powdery anhydrous form. Upon intense heating, it decomposes, releasing nitrogen and forming **potassium and iron carbide. It produces hydrocyanic acid when in contact with acids, and sodium when in contact with bases. It has low toxicity because its cyanide group binds firmly to iron. It is soluble in water, and its aqueous solution decomposes into hydrogen, oxygen, and iron oxide when exposed to light. Insoluble in ethanol and ether. Use: Anti-caking agent. Usage: 1. This product may only be used as an anti-caking agent in certain **. 2. For actual use, this product is usually prepared as an aqueous solution of 0.25–0.5 g/100 mL, which is then sprayed into 100 kg of table salt. Usage: For table salt, the maximum usage amount is 0.01 g/kg (based on ferrocyanide). Toxicity 1. LD50: 1.6–3.2 g/kg (bw) when administered orally to rats. 2. ADI 0～0.025 mg/kg(bw) (based on ferrous **sodium, FAO/WHO, 1994).
Salt these days contains fewer impurities, while larger grains of salt have more impurities!