Review Topics] Use the References to access important values if needed for this

Question

Review Topics] Use the References to access important values if needed for this question It is often possible to change a hydrate into an anhydrous compound by heating it to drive off the water (dehydration) A 34.15 gram sample of a hydrate of CosO4 was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, 18.83 grams of the anhydrous compound remained. What is the formula of the hydrate? Use a period instead of a dot in the formula of the hydrate. Retry Entire Group 9 more group attempts remaining

Explanation / Answer

mass of CoSO4 hydrate = 34.15 g

mass of anhydrous salt = 18.83 g

moles of CoSO4 = 18.83 / 155 = 0.1215

mass of water = 34.15 - 18.83 = 15.32 g

moles of water = 15.32 / 18.02 = 0.850 mol

moles Ratio :

CoSO4   :     H2O

0.1215         0.850

   1                  7

formula of hydrate = CoSO4 . 7 H2O

2)

Fe2O3 + 2 Al    -------------> Al2O3   +   2 Fe

159.69 g      53.96 g

23.9 g             ??

mass of Al needed = 23.9 x 53.96 / 159.69

mass of Al needed = 8.08 g

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