The Amateur Chemist

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How to make Zinc Sulfate from Zinc Oxide


Ingredients
10 grams zinc oxide
115 ml 1 M sulfuric acid


Procedure
The basic idea is that by combining zinc oxide and sulfuric acid a reaction will take place that will make zinc sulfate. 

ZnO + H2SO4 --> H2O + ZnSO4

I tried this using 98% sulfuric acid and just adding it directly to the zinc oxide powder. This however, was an extremely exothermic reaction and blasted powder everywhere. I think this will work much better using a more dilute solution of sulfuric acid. The concentration of choice for me was 1 Molar. 

So to start, weigh out about 10 grams of zinc oxide. Next measure out 115 ml of a 1 M sulfuric acid solution and put it into a 250 ml beaker. Using a spatula, add the zinc oxide to the acid. Only add a little at a time, and stir in between additions of the powder to allow any effervescence to go away. Filter the solution to remove away any unreacted zinc oxide. Put your solution into an evaporating dish to evaporate away most of the water. You can use a water bath for this, and you can even boil it if you want to go faster. One of the sources where I got some info for this prep. said that you should not heat it too strongly, otherwise the solution will decompose. Zinc Sulfate does indeed decompose, but only when dry and at greater than about 680*C. Obviously, you could never achieve this temperature when it is a solution of water. So, go until about 1/5 of the original solution remains.

Then, allow the concentrated solution to cool until crystals form. Filter the crystals and if you want, dab them dry with some filter paper or paper towels. Then, cover them with a clean piece of filter paper and let them dry at room temperature. This should produce around 33 grams of zinc sulfate heptahydrate. I usually only get about 25 grams, but this is because I am too lazy to extract the rest of the zinc sulfate from the remaining liquid after you filter off the other crystals. The crystals produced are quite pretty, being long and narrow and actually quite large. The zinc oxide is in excess here to make sure that all of the sulfuric acid has reacted. 


Here are some pictures of my crystals...


A group of them...