making copper sulphate

[pkij]

Hello all labbies

I have a prac to make copper sulphate with 1M sulphuric acid and copper (II) oxide. The procedure involves heating the sulphuric to 60C then adding CuO until no more dissolves and the pH is neutral. The solution is then filtered and the filtrate copper sulphate is evaporated to allow crystallisation. (The text is Science for Life 9)
I have tried this a few times but cannot get the solution to neutral ph no matter how much CuO I add. The highest ph I could get was 4-5. After a bit of research I found other methods but none of them require the neutral pH.

Ok to get to the bottom of the story, has anyone any suggestions, hints, explanations about this prac.?

Thanks
Pilar

[Jazz]

hi,

i think that neutralise does not mean pH7.
copper II oxide (base) reacts with sulfuric acid (acid) to form salt and water and this is called neutralisation,
as you know acids are defined as proton donors and base as a proton acceptors.

[pkij]

The prac in the book actually asks to test the solution with pH paper, and if it is still acidic to add more CuO. That is where I found it got to the stage I couldnt add any more CuO and the solution was still acidic not pH7

[Jazz]

I work in senior school and I am not familiar with this experiment, that is why I had to do experiment myself to figure out.
I used 0.5M acid and it worked (slower then 1M), it is easier to neutralize (as you said by adding copper ii oxide). oxide. I asked my HOD why we checking pH he said that we have to be sure that no acid remains and If acid has not been hot enough, excess can coexist with copper oxide
hope i got it right this time

[Robb]

Hi All,

Just keep in mind that you need to make sure that the pH does not remain in the Acidic scale. Otherwise the CuO to CuSO4 will just continue to produce the reverseable reaction between the Copper Oxide and the Sulfate of the Copper Ion. We don't want that to happen.

I hope I made that easy to understand.

Cheers,

Robb....