Does anyone know of an example for dehydration reaction?
I am not sure if this counts as a reaction but if you heat up
Copper (II) Sulfate * Pentahydrate, it will turn from a light blue to a tan brown color (the water evaporated) then if you let it set out in the air, it will absorb water and turn blue again. so there you have a dehydration, and rehydration.
do u know of another one?
no, thats just some random thing I remebered from chem. class, but I suppose that there would more if you looked up some more hydrated substances (tri, tetra, penta, hexa, ... hydrate)
Some organic compounds also undergo dehydration reaction, for example, an alcohol can be converted to an alkene by heating with sulfuric acid (a strong dehydrating agent). For example, cyclohexanol, C6H11OH, is converted to cyclohexene, C6H10. There are some other condensation reactions such as Schiff and Knoevenagel condensations, in which water is produced as a side product. All esterification and amidation reactions may be regarded as dehydration from the same viewpoint, but the term generally defines an intramolecular water production.
The synthesis of esters from an alcohol and a carboxylic acid, is an example of a dehydration, though as chem_tr said, this is not the standard case, as H+ comes from the acid and OH- from the alcohol. Some alcohols (especially aldols) dehydrate quite easily into alkenes. Others dehydrate upon heating or in the presence of strong acids.
Dehydration is also used in the purification of organic solvents such as methanol. In such cases, dehydration may be achieved by fractional distillation.
As far as inorganic compounds go, 'dehydration' is simply the process of removal of water from hydrated crystals (that can be achieved by simple heating). Like mrjeffy's example, you can dehydrate crytals of copper sulphate, or calcium chloride or ferrous sulphate by heating them.
There are several other examples, but here's one :
Heating sulfuric acid produces some fumes of sulfur trioxide. Write down this reaction, and you'll see that it is a dehydration reaction.
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