Sciencemadness Discussion Board - Isothermal distillation of hydrochloric acid

Isothermal distillation of hydrochloric acid

DutchChemistryBox - 12-10-2014 at 04:12

Hello,

For a synthesis I want to perform I need hydrochloric acid.
At the moment I only have technical grade hydrochloric acid. I want to purify the acid by isothermal distillation.

My acid is 10%, I want to place it in a closed box together with an equal volume of distilled water, and let it stand for about 10 days. With as goal, to achieve two 5% HCl solutions (one 'dirty' and one without (much) contaminants).

I have read that this is possible for high concentrations of acid. Would this method also work for lower concentrations (10%)?

If I look to the following table: http://www.solvaychemicals.com/Chemicals%20Literature%20Docu... , I would say no. This because the 5% acid has a higher vapor pressure than the 10% acid.

What do you guys think? Should I ignore the vapor pressure and just try it? Or do I need higher concentrations of acid to start with.

I'm not sure or it has anything to do with the vapor pressure, maybe it only depends on the sollubility of the vapors and the vapor pressure is only a indication for the time it needs to get in an equilibrium.

Kind regards,

unionised - 12-10-2014 at 05:10

I'm not sure whether the acid will diffuse into the water or if the water will diffuse into the acid.

Metacelsus - 12-10-2014 at 05:40

Both will happen, but I'd guess that it would be mostly water into acid.

If you have a distillation apparatus (which I highly recommend getting if you don't), you can distill it up to the azeotrope.

blogfast25 - 13-10-2014 at 04:59

Quote: Originally posted by DutchChemistryBox

I have read that this is possible for high concentrations of acid. Would this method also work for lower concentrations (10%)?

What do you guys think? Should I ignore the vapor pressure and just try it? Or do I need higher concentrations of acid to start with.

If you don't actually want to distil then start from technical 37 of 20 w%. Both are quite OTC as drain cleaners, patio cleaners and from various chem distributors.

It will be much faster. But even faster is distilling off the azeotrope (approx. 20 %) from similar concentration 'dirty' HCl.

Or use a HCl generator: NaCl(s) + H2SO4(95 %) === > NaHSO4(s) + HCl(g) and capture the HCl(g) in pure water.

DutchChemistryBox - 13-10-2014 at 07:45

Thank you all for the advices.

Distilling is indeed an option, I do have enough equipment for it.

But I'm conceited, I've thought about it, I'm still going to try it

.
Since I am working as an analytical chemist, it is not really a problem for me to obtain the acid. But I've made a deal with myself, I want to avoid buying reagent grade chemicals as much as possible. It feels much more rewarding if I can 'make/purrify' it myself.

I have read about this method, but I wasn't sure it would work for lower concentrations. After the experiment I will post my titration results, I am really curious about the outcome.
If it doesn't work then it is still a nice learning moment. In that case I'm going to buy it, distilling costs to much effort for a little HCl.

[Edited on 13-10-2014 by DutchChemistryBox]

DutchChemistryBox - 24-10-2014 at 05:14

I've performed the experiment, I opened the box after 17 days.

Just before I was going to titrate, I've checked the pH with indicator paper.
See the picture below, that was enough reason for me to throw it al away, I'm going to buy it.

Nice lesson learnt, it does not really work for lower concentrations.

Left side of the paper in the original solution and the right side in the demi.

[Edited on 24-10-2014 by DutchChemistryBox]