Question

Why we put.between caso4. 2H20

Answer 1

Here is your answer dear friend,


We put . to indicate the attached amount of water molecules with the compound.


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Answer 2

this shows that the given compound is a PRODUCT of these two molecules.
as here,
CASO4 .2H20 ( zypsum) is a product of CASO4 and 2 water molecules (2H2O) .

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