nitroglycol

Mercury is indeed toxic, but I'd use metallic mercury over HF any day. HF is really toxic.

Well, it's a molecule for sure, but most definitions of a compound say that it contains two or more elements. I guess there might be some ambiguity in the definition though. Actually, I have to quibble with this too; sodium chloride is ionic, not molecular (there are no molecules containing one sodium and one chlorine, just a crystal lattice of sodium and chloride ions). But few would hesitate to call NaCl a compound.

Could be magnesium sulphate, but it could also be zinc sulphate or something else. NeonBlack's suggestion of a flame test is a good idea.

Is it really accurate to call it a compound at all? Yes, it has two atoms, but they're both the same element.

Uh... strictly speaking, "acid" is actually a base.

As well, any possibility of posting the design?

Very nicely done!

True of HCl certainly, but nitric acid is actually noticeably weaker. It has a pKa of -1.4, compared to -1.74 for the hydronium ion- so it's only about 93% dissociated in aqueous solution. Which is yet another example of the stronger acid being less corrosive than the weaker one. In this case, what makes HNO3 so nasty is its oxidizing power, not its strength as an acid.