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% H2O of hydration unknown?

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% H2O of hydration unknown?

Post  mgier001 on Fri Sep 16, 2011 11:52 pm

Hi everyone, I'm new to this forum (this is actually my first post!). I have a question regarding my General Chemistry 1 class lab. We had a lab where you had to Calculate the H20 of Hydration of an unknown substance. To do this we measured the constant weight of our crucible by removing all of the water from it, and then weighing our unknown and heating it until it became a constant weight as well. From this we were able to find the weight of the hydrate unknown sample, and the weight of the water lost which gave us the % H2O of hydration in the unknown. Unfortunately during my lab when I was heating my unknown, it got burned (quite a bit ).
Nonetheless, to find out what the unknown is, we have to compare our % H2O of hydration in the unknown to 6 different chemicals (which I will list). I calculated the % H2O of hydration for each of the chemicals and I will list them all below: [by the way: % H2O of hydration= mass H2O/total mass]
CuSO4•5H2O 36.05%
BaCl2•2H2O 14.74%
CoCl2•6H2O 45.41%
Na2CrO4•10H2O 52.63%
MnSO4•H2O 10.65%
MgSO4•7H2O 51.14%

So... when I got my results, my % H2O of my Unknown was 18.32%. Fortunately enough, my professor explained to me that because my unknown was burned, I should look up the chemicals that have a % H2O that were close to my result, and compare the physical properties to those chemicals to find out which my unknown truly is. (It is extremely important that I figure out which unknown is correct because it is worth 5 points out of the whole 15 point lab! ). Anyways, I tried to look up Barium Chloride Bihydrate and Manganese Sulfate Hydrate to find their physical properties but I got all confused and could barely find anything.
The physical properties of my unknown are as follows; when I first got the unknown, it was a very very light pink powder. After heating the unknown and removing the water from the unknown, it looked kind of like a white salt (with a lot of brown because it was burned of course ).
So that's pretty much my big problem, figuring out what my unknown really is. I hope someone here can help me out!
Thank you so very much in advance to everyone ,
Matt.

mgier001

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