# What do these symbols mean?

## I've searched on the web for some of these symbols but I don't know what they mean: 1) $m o {l}^{-} 1$ 2) ${\mathrm{dm}}^{-} 3$ I usually see $m o {l}^{-} 1$ represent "something per mole", but I am not 100% sure of this. If someone could confirm with me, that would be greatly appreciated. Also, for ${\mathrm{dm}}^{-} 3$ , I usually see this unit pop up for concentration questions. My question is, how do I say it? For example, if I am reading a presentation to my classmates, how would I say the concentration of this compound is 1 mol ${\mathrm{dm}}^{-} 3$ ? If someone could also clarify this issue with me, I'd be greatly thankful. Lastly, just out of curiosity are there any other abbreviations that I should be concerned about, for example, $u n i {t}^{-} 2$, $u n i {t}^{-} 4$, etc? Thanks.

You are correct, $m o {l}^{- 1} = \frac{1}{m o l}$ or "per mole".
$\mathrm{dm}$ is a decimetre which is a unit of length. Cubing it gives a volume so ${\mathrm{dm}}^{- 3} = \frac{1}{{\left(\mathrm{dm}\right)}^{3}}$ which is "per volume". You would say "moles per cubic decimetre". Incidentally, a cubic decimetre is the exact same volume as a litre, giving the unit for concentration as $m o l {l}^{- 1}$ ("moles per unit litre") which rolls of the tongue a little bit nicer.