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CuSO4.xH2O -- How to prove value of x?

Can you please tell any experiments that will answer the question copper sulphate.Xwater? I need to have an experiment that gives me X even when I know what X is. thanks 4 your time.

Lauren T.
hobbyist - London, Hertz, England
2003

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There's an interesting student question for a change because I know the value of x, but I don't know how to practically prove it. I guess I would weigh a quantity of it, plate out the copper, and figure out the weight of the copper by a stripping method. If you know the weight of the copper, the molecular weight of each of the elements, and the weight of the material, you can easily calculate x. However, I see practical difficulties with this method and hope someone can suggest a more practical method--perhaps based on reacting the copper or the sulphate with something rather than plating it out. It may also be possible to heat the crystals to drive off 100 percent of the water of hydration, but I don't know the technique.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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Five is the most common value for water of hydration in copper sulphate ⇦ this on eBay or Amazon [affil links] . How you go about proving this will depend on what assets you have and what level of accuracy that you need. A simple way is to weigh a decent sized sample. Spread it in a thin layer on a glass watch glass and bake it overnight at about 200C. Cool it and weigh it. For better accuracy, store it in a desicator with a fair desicant like calcium chloride for a couple of days to remove any moisture on the surface (not the hydrated water).Bake it and then cool it in a vacuum desicator or one with a strong desicant like phosphorus pentoxide. Weigh it. The weight difference is the amount of water of hydration.This weight divided by the original wt will give you a %. Ratio the molecular weights of water and copper sulphate and you can get the X. You can play around with the math at the level of your ability.

James Watts
- Navarre, Florida
2003

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The simplest way is to precisely weigh a known amount of the hydrated salt and then heat it up to about 150-200C, just as James says. Allow it to cool in a dry atmosphere and preferably in a desiccator and then reweigh it. The loss in weight will represent the loss of the water from the hydrated salt. However, I have a sneaking suspicion that even after that treatment the anhydride of copper sulphate still has one molecule of water attached. You should check that out before finally doing your calculations.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003