[hendyn34]

We were given an example lab in which we had to identify an unknown solution from the following possibilities:
hydrochloric acid, sulphuric acid, calcium chloride, strontium chloride, copper (II) sulphate and and copper (II) nitrate.

The solution was unable to distinguish by appearance (normal clear/white solution) so the following tests were perfromed:
A litmus test was conducted, in which blue litmus turned red and red stayed red, so it's obviously an acid.
A flame test was conducted, the flame was mainly green, looked blue green at one point also.
A solubility/precipitate test was conducted. The following reagents were added to samples of the solution:
- SrCl₂, a precipitate formed.
- Ba(NO₃)₂, a precipitate formed.
- Na₂SO₄, no precipitate formed.

So i'm thinking that the unknown solution is either Copper II Sulphate or Sulphuric acid. Copper produces an obvious green flame, but the solution itself never looked blue at any point? However, I don't know what the flame color of sulphuric acid would be.

[Hunter2]

it depends of the concentration. I think its copper sulfate. Do you have ammonia. If yes then add it, the colour should be blue.

[Borek]

If the solution is colorless it is most likely just sulfuric acid. If it is so diluted you can't see blue color of the copper, most of simple tests for copper won't work.

No idea about the flame color though. Any chances it was green for some other reason? Contamination?