Chemistry Help! Hydrates

The anhydrous form of a compound is 38.95 % of the mass of its heptahydrate form. Caluclate its molar mass.

Hi Dave 77!

38.95% =38*1/100 = 0.3895

MM =Molecular Mass

MM(anhydr )/MM(hydrate) = 0.3895

MM(hydrate) = MM(anhydr) + 7*MM(H20)

MM (anhydr )/MM(anhydr) + 7*MM(H20) = 0.3895

Epta- = 7, MM(H2O) = 18

MM (anhydr )/MM(anhydr ) + 18*7 = 0.3895

MM (anhydr )/MM (anhydr )+ 126 = 0.3895

MM (anhydr ) = [MM (anhydr) + 126]*0.3895

MM (anhydr )= 0.3895*MM(anhydr) + 49

MM (anhydr ) - 0.3895*MM (anhydr ) = 49

MM (anhydr )*(1 - 0.3895) = 49

MM (anhydr)* 0.61 = 49

MM (anhydr)= 49/0.61 = 80.33

MM (anhydr)+ 7*MMH2O = 80.33 + 126 = 206.33

Answer:

MM(anhydr)*7 H2O = 206.33 g/mol

Bye from Italy,

C6H6

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