[x_EN]

I'm reading the instructions for a lab, and I'm becoming more convinced that whoever wrote it had no idea what they were talking about. Maybe some of you could shed some light on this.

This was step one:

 1. Take two beakers. In the first, prepare a solution of 76% sulfuric 
    acid, 23% nitric acid, and 1% water. In the other beaker, prepare 
    another solution of 57% nitric acid and 43% sulfuric acid (percentages 
    are on a weight ratio rather than volume).

Ok, I'm sure you see the problem with this. When someone says a solution is 76% sulfuric acid by weight, they mean that for every 100 g of the solution, 76 of those grams are taken up by the H2SO4. With the solution density of 76% sulfuric acid being around 1.5 g/mL, I calculated this to be around 12 mol/L sulfuric acid. The problem is that it claims there is only 1% water by weight. A solution like that would be impossible to make, and 12 mol/L is already incredibly acidic, so I'm going to have to assume that it refers to pouring 76% by weight of a sulfuric acid solution of unknown concentration into 23% by weight of a nitric acid solution of unknown concentration and one percent by weight water. If that is the case (and it's the only thing I can think would be reasonable), then it is entirely useless, as it gives absolutely no indication to the concentrations of these solutions. Thanks a lot.

[nj_bartel]

Looks to be pretty clearly implying % by volume...

[x_EN]

What makes you say that? They didn't specify, so I simply assumed that it was a weight/weight percentage. Even so, the problem still remains. It doesn't tell you the concentrations of the acids. Sure, they ask you to make a solution made up of 76% sulfuric acid, and 23% nitric, but they never specify what concentration these acids would be at (unless they are saying that they want you to add anhydrous acids, ie. 76 mL pure 100% sulfuric acid and 23 mL pure 100% nitric acid and 1 mL water to make an 100 mL solution). In that case they would be referring to fuming nitric and fuming sulfuric acid?

[nj_bartel]

Well, those substances are all liquids.  When you're using just liquids, and it has a %, it's generally % by volume.  AFAIK, there's no such thing as anhydrous sulfuric acid, so I'd say it's implying 98% sulfuric and fuming nitric, but that could be wrong.

[Borek]

I'm reading the instructions for a lab, and I'm becoming more convinced that whoever wrote it had no idea what they were talking about.

Strong words. Not completely unfounded, procedure sounds ambiguous to me. Could be it is built on earlier procedures and some things (which acid to use, how to measure it) are long established at this moment.

AFAIK, there's no such thing as anhydrous sulfuric acid, so I'd say it's implying 98% sulfuric and fuming nitric, but that could be wrong.

That is wrong There is nothing special about sulfuric acid that makes preparation of anhydrous acid impossible. Difficult - yes, as it is highly hygroscopic. Then, we have a trick in a sleeve - we can dissolve excess SO₃ in the acid, to make sure that even if it will catch some water from the air, it will be converted to H₂SO₄.

I think solutions of up to 30% SO₃ in H₂SO₄ are comercially available. Google oleum or fuming sulfuric acid.