John said:
It seems you have obtained fresh and/or have decided your HCl concentration is 19%. That is probably pretty close as constant boiling HCl is 20% by weight.
I just bought the new bottle of HCl (because, allegedly, the shelf life has expired some 11 years ago for my old bottle, although I'm not sure that HCl has shelf-life if stored properly (it was in a plastic bottle with some kind of seal on the cap)). I measured pH (with universal indicator) of my old HCl and it shows pH below +1 !? As I know, 20% (or 6M) HCl have pH of about -0,8 (so, it should be OK). Same result for the new bottle. On that new bottle of "technical HCl" stays 19%, but I saw before that manufacturers mark that "concentration range" as 19-21%. So, it is, in fact, azeotropic solution (about 20±1%). I bought pharmacy grade peroxide of 12% (in my state all the pharmacists MUST have master's degree (one level below doctor's degree), so I can be confident about peroxide concentration. Btw. I simply can't understand why people demand 30 (or even more!)% peroxide??? There is no any need for that concentration, and that is POISON! I can buy (not allways!) in the pharmacy that concentration of peroxide, but only if I give my IDs and put signature in special book (also known as "poison book")! Adults only!
John said:
Also, it is generally recommended to add the acid to the peroxide-water solution.
You forgot that I have pretty much laboratory experience (as I said I studied physics
) - of course, never add water in any acid (except if it is diluted enough)! But, we allways have to repeat that warning, if nothing, because of "young chemists" that make stupid things over and over again (like mixing acetone and H2O2 or so)! And if you have concentrated acid and peroxide (why?) - peroxide is like water - so I agree, first goes water (or peroxide) and than, carefully, add acid. About hydrogen gas production: frankly, I don't remember when I saw that; I personally think that predominant gas in our case is oxigen (as you pointed before), than Cl, HCl(g)...