Sciencemadness Discussion Board

What are splash heads for?

JibbyDee - 4-12-2011 at 09:44

I came across these things called "splash heads" that look like this:

but I can't find any info explaining what they're for. The only info I found says that they are used for distillations in which the condenser is held vertically. I don't get it. Do they mean a reflux setup in which theres a splash head instead of a drying tube at the top of the condenser? In other words you heat the mixture, the vapours go up the condenser and the heavier vapours will be condensed and fall back into the flask while the lighter vapours will reach this splash head. What does the splash head do though?

[Edited on 4-12-2011 by JibbyDee]

Sublimatus - 4-12-2011 at 10:47

My best guess is that it guards against bumping liquid from flying up and out of the vertical condenser.

They make something similar for rotavaps that protects against bumping solvent flying out of the flask and into the condensing chamber.

zoombafu - 4-12-2011 at 13:05

They are just used as an anti-bumping measure, to make sure that your distilled product doesn't get contaminated.

entropy51 - 4-12-2011 at 15:27

Old guys like me know these as "Kjeldahl Bulbs". See In the Kjeldahl nitrogen analysis a sample (often a protein) is digested with acid to convert nitrogen to ammonium salt. This is then made basic with NaOH and the NH3 is distilled into standardized acid and titrated, thus allowing calculation of the amount of nitrogen in the sample. During the distillation the Kjeldahl bulb prevents an aerosol of NaOH from being carried over into the acid absorber and giving a falsely high nitrogen content.

Prevention of bumping being carried over is obviously another use for these.

UnintentionalChaos - 4-12-2011 at 15:53

I believe that the one in OP's post is specifically for kjeldahl nitrogen determination.

peach - 14-12-2011 at 10:29

Steam and other bumpy distillations; e.g. damp oily liquids or under vacuum (rotovaps).

{edit} "What does the splash head do though?" If you haven't run too many distillations before, you might not have encountered bumping, which is when the liquid tends to sit still not boiling, despite being at or over it's BP, and then suddenly boils in a fluster, throwing the contents upwards and towards the still head or receiver. The heads are designed to slow down or stop the passage of liquid phases (bumping) and only allow the vapour through. In a steam distillation, where you might want one of these, you also want two things (with different boiling points) to go through at the same time. So a simple distillation, as opposed to fractional, is needed. A head like this goes on the flask and then a condenser on the other end. {edit}

You can help limit bumping by drying things boiling over 100C prior to distillation, using stir bars or boiling stones (powdered glass), using a half or less full boiling flask, having a column in place (although it won't work so well as a fractioning column if there is persistent bumping), increasing the heat gently (not straight to full) and decreasing the pressure gently. If the thing in question is volatile and boils below 100C, it almost certainly wants cooling down prior to applying any vacuum; or it'll be effectively superheated at the reduced pressure and flash boil (as per dumping instant coffee into freshly microwaved water, or water into a pan of hot oil; it spits all the hot oil back at you as the water boils off).

Drying things can also help you get cleaner fractioning by eliminating the water that might blur the band between solvents and the higher boiling products.

[Edited on 15-12-2011 by peach]

Paddywhacker - 15-12-2011 at 20:40

Naa... it's a bong.

stoichiometric_steve - 18-12-2011 at 15:30

now, that is a ridiculously big bump guard.

hissingnoise - 18-12-2011 at 15:44

It's the picture --- waaay too big!