How could you establish the formula of #ZnSO_4*7H_2O#?

2 Answers
Apr 13, 2017

Answer:

How would you show that it is the #"heptahydrate"#?

Explanation:

Possibly, the best means would be by complexometry.

So, perhaps you would take thesalt, #ZnSO_4*7H_2O#, or one of its several hydrates, and perform a titration with #"EDTA"#.................

And #"EDTA"# reacts with #Zn^(2+)# with 1:1 stoichiometry. With standardized #"EDTA"#, and an accurate mass of the hydrate, you could establish the degree of hydration of the zinc salt.

Apr 13, 2017

Answer:

You could use heat to remove the cristal water.

Explanation:

If you weigh an amount of hydrate and heat it (not too hot!) untill the weigh stays constant, then:

End weight represents anhydrous #ZnSO_4#, which you can convert to mols.

Weight loss represents the cristal water removed, which you also convert to mols.

The ratio of the two gives you the #x# in #ZnSO_4*xH_2O#

Note:
There are three ways this can go wrong:
(1) If you don't heat long enough, not all the water will be gone, and you'll end up with a lower number for #x#
(2) If the sample of hydrated salt is already partly dehydrated, you'll also get an #x# that is too low.
(3) If you heat too long, or too hot, part of the zinc sulphate may disintegrate: #ZnSO_4->ZnO+SO_3(g)# and you will get a value of #x# that is too high.