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Question

Cobalt (II) chloride [CoCl2) the anhydrate [MW = 129.84] is blue. However, it has a hydrate [MW= 237.93] that has a deep red color, used as an indicator for water. Given the molecular weight of water is 18.02 grams per mole, determine the number of waters of hydration for the red colored hydrate. 

Answer 1

Hello Mykayla

 

Anhydrate means "without water."  The difference in mass between the hydrate and the anhydrous compound will give the mass of water (H₂O).

 

mass of H₂O = 237.93 - 129.84 = 108.09 g

 

# of moles of H₂O in the hydrated compound = 108.09 g H₂O x (1 mol H₂O / 18.02 g H₂O) = 5.9983 mol H₂O ≈ 6 mol H₂O

 

 

FYI - The chemical formula of the hydrated compound would be written as CoCl₂ • 6H₂O.