How to prepare zinc sulphate salt?

Question

You are required to prepare dry zinc sulphate salt. The chemicals supplied are

- zinc nitrate solution

- dilute sulphuric acid

- sodium carbonate solution

Describe a laboratory experiment to prepare the salt. In your description, include chemical equations involved. Thank you.

Answer 1

Obviously the best way is to react an excess of Zn metal with H2SO4 and then filter out the solid zinc and evaporate the solution to dryness.

But since you don't have solid zinc, then it is more problematic.

Combine the zinc nitrate with sodium carbonate.  This will produce a precipitate of zinc carbonate.  Allow it to settle and pour off the solution containing sodium ions and nitrate ions.

Zn(NO3)2(aq) + Na2CO3(aq) --> ZnCO3(s) + 2NaNO3(aq)

To the solid zinc carbonate add sulfuric acid.  This will produce water and carbon dioxide along with zinc sulfate in solution.  Evaporate to dryness and you have your dry zinc sulfate.

ZnCO3(s) + H2SO4 -->  ZnSO4(aq) + CO2(g) + H2O(l)

Answer 2

Zinc nitrate is soluble, but so is zinc sulphate. To make it into a form that can be isolated, it has to be converted into an insoluble form first.

This is done by conversion to zinc carbonate, ZnCO3. To do this, mix the zinc nitrate with excess sodium carbonate. The following reactions will occur:

Zn(NO3)2(aq) + Na2CO3(aq) → ZnCO3(s) + 2NaNO3(aq)

Filter off the precipitate and wash it to remove the byproducts and unreacted components. You will be left with pure zinc carbonate.

To convert the carbonate into the sulphate, react the carbonate with sulphuric acid.

ZnCO3(s) + H2SO4(aq) → ZnSO4(aq) + CO2(g) + H2O(l)

The CO2 escapes from the reaction, and the water will be removed when the reaction mixture is allowed to dry. Filter the final mixture to remove any excess zinc carbonate and dry it to remove the water.