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Acids and Alkalis

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.

concentrated
blue copper(II) sulfate                              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.

concentrated
glucose                                       carbon
C₆H₁₂O₆        sulphuric 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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