Doesn't seem to be a problem to me.

The "correct" way to do this problem would be to find out how many moles of CuSO4 there are, which is 5.24/159.6 = .0328 moles.

Then the "MW" of the hydrate can be found by doing grams divided by moles, or 1.77/.0328, which becomes 53.91.

This is some number of water moles, so you divide that by 18 and you get 3.

What you did works perfectly fine. Your teacher was probably just being an a-hole because you didn't learn the "standard" method. :p At least you fought for one point back.

But you should probably use the "standard" method from now on regardless, as there may be times where you won't have enough to do ratios anyways.

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My OOT Parody Thread. "Chapter 71: The Shadow Temple, Part VI- Jailbreak!" has been posted 12/14/08.
[Best Parody Fic S07/W08]