After heating, how many grams of the anhydrous compound remained?

Question

One of the hydrates of CoSO₄ is cobalt(II) sulfate hexahydrate.

A 58.4 gram sample of CoSO₄  6 H₂O was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, how many grams of the anhydrous compound remained?

Answer 1

The dehydration reaction is: CoSO₄ • 6 H₂O → CuSO₄ + 6 H₂O

We see that 1 mole of the hydrate yield 1 mole of the anhydrous compound. So we can use this stoichiometry as follows to solve for the mass the the anhydrous salt.

(154.9 g CuSO₄ / 1 mol CuSO₄) (1 mol CuSO₄ / 1 mol CuSO₄ • 6 H₂O) (1 mol CuSO₄ • 6 H₂O ) / 262.9 g CuSO₄ • 6 H₂O) 58.4 g CuSO₄ • 6 H₂O = 34.4 g CuSO₄