22. "What is left over after evaporating Hydrochloric acid (muriatic acid) in a glass dish?" a) hydrogen chloride precipitate. b) nothing at all c) Chlorine crystals d) table salt Curiously, nobody knew what this answer was...
a). muriatic acid is hydrogen chloride dissolved in water, so evaporate the solution and you get the crystalline solute that was in solution. table salt is what you get if you add NaOH to HCl. and chlorine is, well, a gas (not crystalline solids). if you've ever worked with a bottle of pool acid, you'd notice crusty precipitate around the cap...the remains when the liquid evaporates.
Hydrochloric acid will completely evaporate. There is no such thing as crystaline HCl - it is a gas. Hydrochloric acid is HCl gas dissolved in water. When you evaporate the acid, water will evaporate off first (a little HCl will always vaporize too) until the solution is saturated (ie, max concentration) then both water amd HCl will vaporize in equal proportions until neither is left. The answer is B.
I've ended up with carbonate salts (my mistake, muriatic is typically hydrogen chloride gas is dissolved in DI water) on the cap, probably because of where I stored it. dilute hcl may undergo carbonation upon prolonged exposure to air. in inert conditions, it'll evaporate cleanly. HCl gas would actually evaporate first, it has a higher vapor pressure.
Actually, a negative azetrope, so that the vapor pressure of aqueous HCl is no longer a function of its two components. HCl and water are polar and once in solution, the bond between the two is so strong that when the mixture is boiled H20 escapes more readily than the HCl, even though HCl is a gas with a boiling point some 150C below water's. Most hydrogen halide acids (hydrofluoric is a little funky) have a maximum boiling point that represents a specific w/w concentration. Hydrochloric is 20% at 108C. Hyriodic is 57% at 127C. A more dilute hydrochloric acid will boil off mostly water at a temperature below 108C until it reaches a stable 20% concentration and boiling point until it is entirely boiled away. A more concentrated acid will boil off mostly HCl at a temperature below 108C until it reaches that stable 20%. Notice how in either case, the solution boils at a lower tempurature until it reaches 20%. As for any residue from CO2 or other airborne molecules, you still need a cation to fix a non-volatile salt - some volatile base. I suspect ammonia or organic amines as the most likely culprit for residue after evaporating pure hydrochloric acid, especially if your experiment is conducted in a bathroom or near the kitty litter (urine is the prime household source of organic amines). You could test your residue with a drop of concentrated NaOH or a lye crystal and water and see if you catch the unmistakable whiff of ammonia.
that's probably what it was.. I likely stored it near ammonia, in a quite warm environment (garage). also true about the 20% equilibrium, I was taking conc. hcl (>6M) into account
Yah. this accomplished alot. Now Im lost. Polymer, who says he's a chemist, says "residue" The other guy, who sounds like a chemist, corrects him and says "nothing" In an acid/base extraction, if hcl is used to precipitate the salt and the novice chemist overuses it somewhat to push the collection water to an acid ph: when evaporated there WOULD or WOULD NOT be a potentially harmful byproduct in the final result???...i.e. salt form+? Obviously, swim needs to get a glass of room temperature muriatic acid and wait for it to evaporate while watching the grass grow... :ack: Could we dumb the answer down a wee bit? Next time post; bring pie...
...And if I do it in an enclosed space, Ill end up with less brain cells than what I started with... got it... :toetap:
haha...sorry, it was my brilliant post of the day. I usually try to keep the pH at 3 and 9 in a/b extractions. end product extraction between 6 and 7. pH around 7 is optimal, where ionic salts form (i.e. hcl salts)
Ph 7 is neutral. End product would be extracted with ph 3 H2O added in small amounts to your xylene dissolved freebase mescaline, until extraction water ph reaches neutrality 7,after a period of ph stabilization, or just faintly goes acidic (ph 6) whereupon water is evaporated, leaving, hopefully, only your crystalline salt product and nothing else. Like, say, Hydrogen Chloride precipitate. Option A? Or cat piss carbonate? Mmmm. Yummy... Got it. Defcon 1. Fire the missiles. Vive la Canada!!! :huh:
If you're going to drive yourself nuts trying to titrate your project into perfected infinity, you should do a proper A/B extraction, including washing your loaded polar layer with dilute NaOH, and your loaded aqueous with xylene - and definately do not end the process by evaporating water to get your salt. Acidify the xylene to precipitate your salt and your product will be so so so much cleaner.
the xylene will not acidify, per se, but I know what you're saying: add hcl (or H2SO4) dropwise to the xylene, after separating it from the basic aqueous phase. tried it once, doing exactly this sort of extraction: I once made the ridiculous mistake of sticking my hanna digital pH meter in xylene..doh..the xylene was neutral, of course, and the plastic eroded some. still works, though
There is a reason why they say its an art. I had thought that meant one thing and I had also tried to apply classroom type logic, but gut instinct cannot be replaced. The chem rules make far more sense ad hoc. structure charge lg etc. What is taught anti-intuitive turns out to be really intuitive. I can take a salt of an organic molecule, dissolve it in water and then let it evaporate to get the salt back, yet it doesn't work the other way.
