(1) Absorbing water, a bottle of concentrated sulphuric acid is placed in the air, its mass will be added, its density will be reduced, its concentration will be reduced, and its volume will be increased. This is because concentrated sulfuric acid is water-absorbent, and it is often used as a drying agent in the laboratory.
Concentrated sulphuric acid can absorb not only water in air, but also water vapor mixed in gas, wet water mixed in solid and part of crystalline water in hydrate.
The H2SO4 molecule in concentrated H2SO4 can absorb free water molecules intensely to form a series of sulfuric acid hydrates. These hydrates are very stable, so concentrated H2SO4 can be used as a dry agent for some gases and solids that do not react with them, and can not be exposed to the air at the same time. Thick H2SO4 can be used to dry gases such as acidic or neutral gases, while recoverable gases such as NH3 and alkaline gases can not be used to dry gases such as thicker H2SO4. In addition, in esterification reaction, such as medium, concentrated H2SO4 as catalyst and water absorbent.
(2) Dehydration refers to the property that concentrated H2SO4 removes oxygen and oxygen elements from organic matter at the atomic number ratio of 2:1 to form water. Concentrated H2SO4 takes off the atoms of hydrogen and oxygen from organic matter, not water. The atoms of dehydrated hydrogen and oxygen form hydrogen peroxide in a ratio of 2:1. Concerning the organic matter (such as sucrose, cellulose, etc.) whose number ratio of hydrogen and oxygen atoms in molecule is 2:1, concentrated H2SO4 can make its carbonization black, such as:
(3) At ambient temperature with strong oxidation, Fe and Al will be passivated when H2SO4 is concentrated. However, hot concentrated H2SO4 oxidizes most metals (except gold and platinum), some non-metallic elements and some resilient compounds. Such as:
In these oxidation recovery reactions, the recovery product of concentrated sulfuric acid is usually SO2.
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