Exercise 3. The Purification of Copper Sulfate

As a preliminary experiment to prove that simple recrystallization will not remove ferrous sulfate from copper sulfate, proceed as follows  

Dissolve 500 g. of commercial copper sulfate (blue-stone) in 1.5 1. of boiling water in an evaporating dish, add 3 g. of ferrous sulfate (unless this is known to be present as an impurity), and allow the solution to cool. Select about 1 g. of the crystals that form and test them for iron. To do this, dissolve the material in 10 cc. of water, add about 2 cc. of concentrated nitric acid, and boil for a few minutes. Cool the solution and add 

Drain the crystals of copper sulfate that have by this time accumulated in the original solution, if necessary evaporating the mother liquors from them to secure a second crop of crystals. Secure about half of the original material in this form and set aside the mother liquor for future use. Recrystallize the salt as in the original procedure, using a proportionate quantity of water. Again test a specimen of the crystals obtained for iron and convince yourself that it is still present. Those experiments show that the ferrous sulfate is not removed by several crystallizations. 

Drain the crystals on a bare Witte plate or a Buchner funnel, wash them once or twice with small portions of cold water, and spread them to dry on clean filter paper supported on a glass plate. A second and third crop should be secured from the mother liquor. 

References on CuS02-5H20 Friend, II, 279 Mellor, III, 240 Krauch, p. 90 Murray, p. 225 Foote, Am. Chem. J., 26, 418 (1901) Hopkins, 

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