# The least dense liquid on Earth **URL:** \ **Category:** Factual Questions\ **Created:** [October 30, 2000, 4:18pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940 "2000-10-30T16:18:02Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![corpuient](https://avatars.discourse-cdn.com/v4/letter/c/838e76/32.png) [@corpuient](https://boards.straightdope.com/u/corpuient)\ **Post date:** [October 30, 2000, 4:18pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/1 "2000-10-30T16:18:02Z")
What is the least dense liquid on Earth, the liquid that will float on any other? ---
**Author:** ![SIA\_Sorry\_I\_Asked](https://avatars.discourse-cdn.com/v4/letter/s/f08c70/32.png) [@SIA\_Sorry\_I\_Asked](https://boards.straightdope.com/u/SIA_Sorry_I_Asked)\ **Post date:** [October 30, 2000, 4:30pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/2 "2000-10-30T16:30:48Z")
And while you’re at it, please explain why a large molecule like alcohol can float above a small molecule like water. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [October 30, 2000, 5:36pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/3 "2000-10-30T17:36:04Z")
At what temperature and pressure? Do you mean under normal conditions, or standard temperature and pressure? I think naptha may qualify as the least dense common liquid one would find under relatively normal conditions, as it can be as low as 0.665 g/cm[sup]3[/sup]. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [October 30, 2000, 5:45pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/4 "2000-10-30T17:45:05Z")
I am pretty sure there was a question here not too long ago that asked if there was a liquid so think that a person could not swim in it. I would think your answer might be in there. However, I’ve tried searching the word _swim_, _float_, and _liquid_ but I can’t find the thread. Maybe someone else who remembers it better? Good luck. ---
**Author:** ![TNTruth](https://avatars.discourse-cdn.com/v4/letter/t/d9b06d/32.png) [@TNTruth](https://boards.straightdope.com/u/TNTruth)\ **Post date:** [October 30, 2000, 6:15pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/5 "2000-10-30T18:15:48Z")
For the record, liquid hydrogen, with a specific gravity of .07 But, since its boiling point is -253 C, you don’t have to worry about sinking in it. I think Anthracite nailed it for liquids at STP, I couldn’t find anything under .5 sg. As far as floating in a liquid less dense than water, that was covered recently in a thread about oil. And, yes, you will sink like a stone. ---
**Author:** ![peace](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@peace](https://boards.straightdope.com/u/peace)\ **Post date:** [October 30, 2000, 6:23pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/6 "2000-10-30T18:23:37Z")
One liquid can float on another liquid only if they do not mix (like oil and water). Otherwise, their specific densitied do not matter. Specify your question please. Indicate temperatures, etc. TIA. ---
**Author:** ![\_Tim](https://avatars.discourse-cdn.com/v4/letter/_/e47c2d/32.png) [@\_Tim](https://boards.straightdope.com/u/_Tim)\ **Post date:** [October 30, 2000, 11:52pm UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/7 "2000-10-30T23:52:32Z")
Using the liquid at STP criterion, 2-methyl butane, which boils just over STP at 27.8 C, has a density of .6201 at 20 C. That’s the best I found. Here’s a list of some straight-chain hydrocarbons: Hexane .6603 at 20 C Pentane .6262 at 20 C Butane .5788 (20 C, elevated pressure; boils at -0.5 C) Propane .5853 (at -45 C; boils at -42.1 C) Butane and propane both violate the liquid at STP rule, but they have the advantage of being familiar to the general public as pressurized liquids in spite of this… For a low density liquid, you need something which is not very dense by itself (containing mostly lighter atoms) and which has fairly weak intermolecular interactions, so that the individual molecules are widely spaced in the liquid. Hydrocarbons are quite nonpolar (which means weak intermolecular interactions) and contain no atoms heavier than carbon, so are good candidates. Basically, the smallest ones which are liquid at room temperature are the best. 2-methyl butane and pentane are made of the same number of atoms(C5H12), so are close to each other in density and melting point. Incidentally, there are some boron hydrides that are close but don’t quite fit the STP criterion; Dihydrotetraborane (B4H10) has a density of .56 at -35 C but boils at 16 C. Pentaborane(B5H9) is liquid at STP but has a density of .66. Too few hydrogen per heavy atom for a low density liquid, I guess. They’re also hard to study, as they explode if they come in contact with air… ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [October 31, 2000, 12:17am UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/8 "2000-10-31T00:17:41Z")
> [@](#): > > \*Originally posted by (Tim) \* > **Using the liquid at STP criterion, > 2-methyl butane, which boils just over STP at 27.8 C, has a density of .6201 at 20 C.** **Damn you** , 2-methyl butane! You’ve beaten me again! 🙂 ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [October 31, 2000, 3:42am UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/9 "2000-10-31T03:42:57Z")
> [@](#): > > there was a liquid so think that a person could not swim in it A really dense liquid? My guess would be mercury. I seem to remember that iron will float in it. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [October 31, 2000, 4:03am UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/10 "2000-10-31T04:03:30Z")
> [@](#): > > \*Originally posted by Sunspace \* > **A really dense liquid? My guess would be mercury. I seem to remember that iron will float in it.** I saw an earthquake-dampening weight system used in a building in California (on TV) where they employed a large granite block floating in a pool of mercury. With its very high density, I’m sure one would float very well in mercury. Just don’t inhale those vapors… ---
**Author:** ![peace](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@peace](https://boards.straightdope.com/u/peace)\ **Post date:** [October 31, 2000, 4:09am UTC](https://boards.straightdope.com/t/the-least-dense-liquid-on-earth/38940/11 "2000-10-31T04:09:45Z")
Corp, I think the time came for you to look under spesific density yourself. But you are silent, probably lost interest.