Can a separatory funnel be used to collect a precipitate, or would that risk clogging the stopcock on it?

I'd like to recoup the precipitate for filtering without passing the entire solution through a filter (to avoid contaminating it, and also for convenience / saving time).

  • $\begingroup$ Most times you'll just jam the stopcock. Filter it first. $\endgroup$ – Waylander Jun 12 '19 at 8:27
  • $\begingroup$ @Waylander Thanks for your answer! :) $\endgroup$ – Veritas Jun 12 '19 at 8:30
  • $\begingroup$ If your wrote what kind of precipitate you are trying to recover, one could give better answers than "that's likely to go wrong". $\endgroup$ – Karl Jun 12 '19 at 22:24
  • $\begingroup$ @Karl: Thanks for this tip / specific feedback. It's useful to me in the process of learning how to best use this platform. As for the question, I was not thinking of any precipitate in particular but wondering if it would be smart to invest in a reparatory funnel in the prospect of using it for different purposes, and thus wondering if one of these purposes, in addition to separating liquid phase matter, could also be to conveniently extract the small fraction of a solution in which most precipitates are located (generally, with any precipitate). ANSWER CONTINUES HEREAFTER ⤑ $\endgroup$ – Veritas Jun 12 '19 at 22:31
  • $\begingroup$ Now pragmatically, the most likely precipitates I would be dealing with in an immediate future would be ordinary metal carbonates or metal salts. $\endgroup$ – Veritas Jun 12 '19 at 22:33

Good thought, but Waylander is correct.

However, you might consider centrifugation to consolidate the ppt, then pour off the supernatant. If you don't have a centrifuge, and the quantity of liquid is not too large (100 mL or less), you could make your own, since it seems that your ppt settles fairly fast.

Put the solution in a tough plastic bottle, cap it, and get a pretty strong string or light rope, tie the bottle SECURELY and twirl it over your head. Maybe outdoors is better for this, unless you are very careful. A few gentle swings (~20) should be enough, if it is going to work at all. I have had some success with this method a few times.

Secure tying is key, since the extra Gs will put a strain on your knots. I did something like (vertical swing, about 4 foot circle) this inside a room with 12 foot ceilings, and the plastic bottle hit the ceiling and splashed (I did not have the cap on). Fortunately, the stain was not very noticeable, but I did lose some of the material.

  • 2
    $\begingroup$ Don't do that outdoors, unless your material is water-based and environmentally harmless. You don't want to get an invoice for five cubic meters of soil that had to be dug up and disposed as hazardous waste. $\endgroup$ – Karl Jun 12 '19 at 22:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.