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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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OldSpice OldSpice
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9 years ago
An unknown hydrate of cobalt(II) cyanide, Co(CN)2 • XH2O, is heated to give 32.7% water. What is the water of crystallization (X) for the hydrate?
A) 2
B) 3
C) 4
D) 6
E) 10
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ElectricElectric
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9 years ago
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.silent.boss

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OldSpice Author
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#2
9 years ago
Perfect!

..Thank you so much for your support
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#3
9 years ago
My pleasure
.silent.boss
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#4
A year ago
The game plan with these is to figure out the number of moles of H2O there are per mole of CaSO4. Start by assuming any quantity of CaSO4 X H2O.

Assume 100.0 g of CaSO4 XH2O.

20.9 % of that = 20.9 g
That is the mass of water.
1 mole of water = 18.0 g
20.9 g x 1 mol/18.0 g = 1.16 mol H2O

100 % - 20.9 % = 79.1 % CaSO4
79.1 g is the mass of CaSO4
1 mole of CaSO4 = 40.1 + 32.1 + 4(16.0) = 136.2 g
79.1 g x 1 mol / 136.2 g = 0.581 mol CaSO4

Now calculate the ratio of mol H2O to mol CaSO4
1.16 / 0.581 = 2.00
So X = 2
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