Some compounds may be occur in a hydrated form, with the primary compound complexed with water molecules. The weight of the additional water molecules needs to be considered in determining the dose of the hydrated versus the nonhydrated compound.


Example: ferrous sulfate is often formulated as the heptahydrate



(1) molecular weight unhydrated

(2) number of water molecules involved


molecular weight of hydrated compound in grams =

= (molecular weight of nonhydrated compound) + (18 * (number of water molecules in hydration)


ratio of nonhydrated to hydrated formulations =

= (molecular weight nonhydrated) / (molecular weight hydrated)


amount of nonhydrated compound to dose =

= (dose of hydrated form) * (ratio of nonhydrated to hydrated)


amount of hydrated compound to dose =

= (dose of nonhydrated form) * (1 / (ratio of nonhydrated to hydrated)


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