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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: CSG on May 10, 2010, 08:21:34 PM

Title: Hydrate problems
Post by: CSG on May 10, 2010, 08:21:34 PM
Hi, I would be very grateful if anyone could show me how to answer the following question:

The value of x in Fe(NH4)2(SO4)2. xH2 O can be found by determining the amount in moles of sulfate in the compound.
A 0.982g sample was dissolved in water and excess BaCl2 (aq) was added.
The precipitate of BaSO4 was separated and dried and found to weigh 1.17g.

(a) Calculate the amount, in moles, of sulfate in the 0.982g sample of Fe(NH4)2(SO4)2. xH2O

(according the the answers it's 0.00501 which I do not understand)

(b) Calculate the amount, in moles, of iron in the 0.982g sample of Fe(NH4)2(SO4)2. xH2O

(apparently the answer is 0.00250 which is half of the previous answer - why?!)

Thanks in advance.
Title: Re: Hydrate problems
Post by: Borek on May 11, 2010, 02:55:22 AM
Quote from: CSG on May 10, 2010, 08:21:34 PM
The precipitate of BaSO4 was separated and dried and found to weigh 1.17g.

How many moles is that? How many moles of SO42- per mole of BaSO4?

Quote
apparently the answer is 0.00250 which is half of the previous answer - why?!

How many moles of SO42- per mole of Fe(NH4)2SO4?