What is the least dense liquid under normal conditions, room temperature, one atmosphere of pressure, doesn't combust upon contact with air, also wouldn't kill a human just for being in the same room as it?


Isopentane $\ce{C5H12}$ has the density of $0.6201~\mathrm{g\,cm^{-3}}$ at $20~\mathrm{^\circ C}$ [1, p. 3-330].


  1. Haynes, W. M.; Lide, D. R.; Bruno, T. J. CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data.; CRC Press, 2017; Vol. 97. ISBN 978-1-4987-5429-3.
  • $\begingroup$ That is... surprisingly dense. Water is known to be 'heavy' in common speech, but there aren't really any liquids which are a lot lighter apparently. $\endgroup$ – orlp Apr 25 '19 at 8:11
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    $\begingroup$ @orlp That's due to the constraint imposed by OP: the compound must be liquid at NTP conditions. Once the constraint removed, there are more interesting things such as solution of lithium metal in liquid ammonia or good old liquid hydrogen with the density of $0.0709~\mathrm{g\,cm^{-3}}$, but that's not what the question is about. $\endgroup$ – andselisk Apr 25 '19 at 8:16
  • $\begingroup$ @andselisk The famous blue solution is significantly lighter than plain liquid ammonia? $\endgroup$ – Karl Aug 6 '20 at 19:10

According to

Hans Jaffe: Eine metallische Verbindung von Lithium mit Ammoniak. Elektrische Leitfähigkeit und galvanomagnetische Effekte. Z. Physik 93, 741–761 (1935) https://doi.org/10.1007/BF01337859

the saturated solution of lithium in liquid ammonia (approx. $\ce{4NH3 \cdot Li}$) has a boiling point above RT, and is significantly less dense (=0.48g/ml) than isopentane (0.62), or plain ammonia (0.77):

... Mit einer Dichte von 0,48 ist die gesättigte Lösung von Li in NH3 die leichteste bei Zimmertemperatur existierende Flüssigkeit. Die feste Verbindung ...

I wasn´t able to get the full text, unfortunately. And yes, there is a possibility for it to ignite if not handled under an inert atmosphere. How dangerous I don´t know.

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    $\begingroup$ You could allow non-german speakers who read your answer look for a translation elsewhere (not that the more clever readers wont intuit the meaning), or .... "... With a density of 0.48, the saturated solution of Li in NH3 is the lightest liquid that exists at room temperature." $\endgroup$ – Buck Thorn Aug 6 '20 at 19:25
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    $\begingroup$ @BuckThorn Well, whoever doesn´t get it now finds the translation right underneath. :-) $\endgroup$ – Karl Aug 6 '20 at 19:32
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    $\begingroup$ What a wonderfully unexpected answer! $\endgroup$ – Nicolau Saker Neto Aug 7 '20 at 2:57
  • $\begingroup$ @NicolauSakerNeto All thanks to anselisks intriguing comment below! $\endgroup$ – Karl Aug 7 '20 at 7:16

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