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Acids and Alkalis

What is Dehydration?

Dehydration means removing water from a substance.
Concentrated sulfuric acid is very good at dehydration.

Example 1.
Blue copper(II) sulfate crystals contain water.
Five water molecules surround each copper sulfate particle.
Concentrated sulfuric acid takes away the water molecules
and the copper sulfate becomes white.

blue copper(II) sulfate              arrow          white copper(II) sulfate
CuSO4(5H2O)         sulfuric acid                    CuSO4

White copper(II) sulfate is called anhydrous
and is used as a test for water.

Example 2.
Glucose is a sugar which is made in
the leaves of plants during photosynthesis.
It does not contain water molecules but does contain
hydrogen and oxygen which are the elements of water.
Glucose has the formula C6H12O6.
Concentrated sulfuric acid will take away the elements of water
from glucose leaving only carbon.

glucose               arrow                    carbon
C6H12O6        sulfuric acid              C      

The water which is removed in these examples
dissolves in the concentrated sulfuric acid and makes it more dilute.

See also the dehydration of ethanol.

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