I was also wondering how to distinguish between these acid pairs:
(a) Hydrobromic or hydroiodic acid
Bubble Cl2(g) through a solution of HI(aq) and will evolve I2(g), which is purple in colour but through a solution if HBr(aq) will evolve Br2(g) , which is brown in colour and will also layer above I2(g) because it’s molecular weight is lighter. Test the pH because HI will have a stronger degree of dissociation than HBr because of its electronegativity
(b) Sulfuric or nitric acid
NH3(g) + HNO3(aq) --> NH4NO3(s)
Bubble NH3(g) through HNO3(aq) will give NH4NO3(s), which is an explosive.
NH3(g) + H2SO4(aq) --> (NH4)2SO4(s)
But bubble NH3(g) though H2SO4(aq) will give (NH4)2SO4(s), which is a flame retardant.
(c) Hydrochloric or acetic acid?
HCl(aq) + AgNO3(aq) --> AgCl2(s) + HNO3(aq)
Mix with AgNO3(aq) to precipitate a metal salt, AgCl2(s), that can be heated to produce silver metal and pale yellow-green chlorine gas.
CH3COOH(aq) + AgNO3(aq) --> CH3COOAg(s) + HNO3(aq)
Mixing with AgNO3(aq) to precipitate a metal acetate, CH3COOAg(s), that won’t produce metallic silver or a pale yellow-green gas when heated but will give an offensive taste in the presence of cigarette smoke.