Why liq. NH3 cannot be used as a leveling solvent for NaOH and NaNH2?
If you really want to make a solution of HClO3, then indeed the way to go is reaction of dilute sulphuric acid with barium chlorate. Another option, which gives fairly pure HClO3 is mixing a hot solution of KClO3 with a hot solution of HClO4. On cooling down, KClO4 is formed. When the liquid is cooled to well below zero, then 99% or so of all KClO4 precipitates from the liquid. Use a slight excess of HClO4 and the resulting liquid will be almost free of any potassium. At concentrations of 20% or so, a solution of HClO3 is quite stable and then it may be hot. At 35% to 40% the solution already is much less stable and then heating leads to disproportionation to HClO4, ClO2, Cl2 and H2O. You can easily see this, the liquid then turns yellow.
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