White Yeti - 26-7-2011 at 13:47
I accidentally dropped some CaCl2 flakes into some acetic acid and it started bubbling. Did I make hydrogen chloride gas? If so, why hasn't anyone
thought of mixing these two substances together to make HCl on demand?
Furthermore, I test for hydrochloric acid and I get negative results.
The funny thing is that I tried this again using salt instead of CaCl2 and nothing happens.
Can anyone reproduce this procedure and explain what is going on?
Thanks.
#maverick# - 26-7-2011 at 15:27
What did it smell like. HCL has a very foul and irritating smell
bahamuth - 26-7-2011 at 15:43
Heat of dehydration, if the CaCl2 was anhydrous and the acetic acid not...
White Yeti - 27-7-2011 at 07:03
I didn't try to smell it because there was very little of it bubbling up in comparison to how much chemical I used. This probably meant that most of
it was dissolving. But in that case, would this reaction be some kind of equilibrium, since the HCl remains dissolved (most of it)?
Mixell - 27-7-2011 at 07:08
HCl is a lot stronger acid than acetic acid, so CaCl2 shouldn't produce HCl on contact with acetic acid, may be the bubbles were HCl, that just gassed
out due to some equilibrium because of the heat cause by the fast addition of the flakes. I you would add them in very small amounts over some time
with stirring, I would expect no gas to form at all.
not_important - 27-7-2011 at 08:17
As said above, HCl is far the stronger acid of the pair : pKa of -6 to -8 depending which reference vs pKa of 4.75 or so for acetic. It would take
rather special conditions to overcome that 11 or 12 orders of magnitude difference in acid strengths.
Commercial tech grade CaCl2 often contains a trace of CaO from loss of HCl during drying. It it sits around long enough iut will pick up atmospheric
CO2 (may gases diffuse through plastic containers or CO2 is fairly non-polar), turning into CaCO3 - which will react with acetic acid.
bbartlog - 27-7-2011 at 18:26
What was your source of CaCl2? If it's ice melt or some other commercial grade then the bubbles are almost certainly due to contamination with
Ca(OH)2, CaCO3, CaS or the like...
White Yeti - 28-7-2011 at 04:51
Yes, I used commercial grade. So this reaction might have been contamination with other calcium salts.