[Big-Daddy]

If sulphuric acid and a little nitric acid, highly concentrated, are added to solid zinc oxide, and then the solution is heated, we get a white precipitate on cooling. Write a reaction equation for this process.

I can't think of anything else but ZnSO₄ but this is soluble too ... so what is the answer? ZnNO₃ is soluble of course.

[billnotgatez]

Just tinkering

Zinc_oxide
http://en.wikipedia.org/wiki/Zinc_oxide
ZnO

Sulfuric_acid
http://en.wikipedia.org/wiki/Sulfuric_acid
H₂SO₄.

Nitric_acid
http://en.wikipedia.org/wiki/Nitric_acid
HNO₃

Zinc oxide is an inorganic compound with the formula ZnO. ZnO is a white powder that is insoluble in water,

ZnO + H₂SO₄ + HNO₃ 

[billnotgatez]

http://en.wikipedia.org/wiki/Zinc_sulfide
says

Zinc sulfide (or zinc sulphide) is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various impurities, the pure material is white, and it is widely used as a pigment. In its dense synthetic form, zinc sulfide can be transparent, and it is used as a window for visible optics and infrared optics.

ZnO + H₂S  ZnS + H₂O

But maybe you can write a formula for any possible reactions?