[the_little_angel]

today i did an experiment at home. It was really strange that it was a reaction of Copper oxide and H₂SO₄.Theoretically, there must be H₂O and Sulphate Copper made from that creation. But when I fired the solution, there was something black and brown. I dipped a piece of litmus paper in it, it was crimson. Who can explain it to me?

[billnotgatez]

Copper(I) oxide (cuprous oxide, Cu2O), a red powder.
Copper(II) oxide (cupric oxide, CuO), a black powder.

Which of these did you have?
Are you sure it was pure
Was the sulfuric acid pure?
Could you write a balanced equation (just for grins)?

I am curious

[the_little_angel]

i used copper(II) oxide (I think we usually think of copper(II) when we mention it without the valence). Theoretically, a reaction of an acid oxide and an acid makes a salt and water.
CuO + H₂SO₄ -> H₂O + CuSO₄
I've read a lot of books to check this equation. It exists. But I'm not sure my copper oxide and sulphuric acid are all pure.

[the_little_angel]

no more explanation for this?

[billnotgatez]

In this case, unfortunately I am not knowledgeable as well

I am curious

[the_little_angel]

that's ok. I have one more thing to ask: what's the color of copper chloride? I combined CuO and HCl together, it made a green solution.

[Donaldson Tan]

Did you use concentrated HCl? CuCl₄^{2-[/sub] is a green complex which forms in the pressence of excess chloride ions.}

[UnintentionalChaos]

How concentrated was the H2SO4? Anhydrous CuSO4 is white or grayish and the color could easily be affected. This would be the majority product if you used conc. H2SO4. If this is the case, dilute some in water and see if you get blue.

[the_little_angel]

thanks very much. Yes, that's right, i used concentrated HCl. I couldn't explain how could CuCl₂ be green instead of blue. It wasn't CuCl₂, was it?

[UnintentionalChaos]

In concentrated solution, a good deal of the copper (II) chloride acts like "copper (II) tetrachlorocuprate (II), which is still two copper and 4 chlorine, so the formula is the same. Tetrachlorocuprate ion I think is bright yellow and combined with the normal blue color of the water coordinated looks deep green. If you dilute the green solution, it reverts to blue as the equilibrium is shifted toward water-coordinated copper ions.

My last post was about the copper sulfate from the original question.