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I'm entirely chemically-naive and am confounded when trying to convert $\ce{NaCl}$ brine concentrations to moles per litre.

The situation is that I'm performing linear multiple regressions using published data form multiple studies. Because the studies report their brine concentrations using different units I am trying to convert all of the concentrations into molarity (moles per litre). To do that I'm using the conversion tool at EndMemo - here's a screen shot:

enter image description here

But in more than one place in the literature people report different M values ... for example, below is an extract from one of the studies. Their M values don't match what I'm getting using the online converter (for example, 4 g/L $\ce{NaCl}$ is coming out as 0.068 M/L...hopefully I'm missing something very basic here?)

enter image description here
(Broseta D., Tonnet N., and Shah V., Geofluids, 2012, 12 (4), 280-294.)

As an aside, I'm not finding consistency with the unit symbols for Molarity and litre (sometimes they are capitalised, sometimes they are not...are they referring to different things or is this another example of inconsistency)?

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  • $\begingroup$ Welcome to chemistry.se! If you have questions about how to beautify your posts, have a look at the help center. Do you want to know more about this site, please take the tour. $\endgroup$ – Martin - マーチン Feb 24 '15 at 4:25
  • $\begingroup$ As for the last part, the notation for litre is $\mathrm{L}$, but $\mathrm{l}$ is also allowed. The amount concentration (molarity) may be abbreviated with $\mathrm{M}$, but since this is not official or standard notation, everybody does what she or he wants, so it's just inconsistency. (I personally do very, very much dislike the use of an abbreviation for molarity.) $\endgroup$ – Martin - マーチン Feb 24 '15 at 4:33
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    $\begingroup$ I do also believe, they messed up in the paper you excerpted, your calculation is correct and their use of concentration questionable. As $\mathrm{M}$ refers to $\mathrm{mol\cdot L^{-1}}$, there should not be an extra $\mathrm{L^{-1}}$. Could you add the full reference to the paper, so we can look up the context. $\endgroup$ – Martin - マーチン Feb 24 '15 at 4:43
  • $\begingroup$ The extract is from page 283 of: Broseta D, Tonnet N, Shah V. 2012. Are Rocks Still Water-Wet in the Presence of Dense CO2 of H2S? Geofluids 12, 280-294 $\endgroup$ – lithic Feb 24 '15 at 4:53
  • $\begingroup$ The original unit symbol for the litre (a non-SI unit that is recognized by the CIPM as having to be retained for use together with the SI) is a lower case l because it is not derived from a proper name of a person. Only this original symbol is used by ISO, IEC and corresponding national standards. However, by way of an exception, the CGPM has approved the two symbols l and L due to the risk of confusion between l and 1 in some fonts. According to IUPAC, also by way of an exception, the symbol may be either L or l. … $\endgroup$ – user7951 Feb 24 '15 at 15:22
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example, 4 g/L $\ce{NaCl}$ is coming out as 0.68 M/L...hopefully I'm missing something very basic here

Yes, you are off by a factor of 10.

4 g/L $\ce{NaCl}$ is 0.068M (0.068 moles per liter of solution).

As far as the journal article, I would used the 4 grams per liter value (and other grams per liter values) and convert to moles per liter properly and not rely on the 0.08 (small capital "M" l-1) value.

If the value is critical to your research, email the corresponding author of the paper and and ask about it in a polite way.

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  • $\begingroup$ Thank you for the clarification and the advice, I'll do as you suggest. I had written the wrong value in the original post- I did have 0.068 for 4 g/L (and 0.68 for 40 g/L) - and have updated the original post accordingly. $\endgroup$ – lithic Feb 24 '15 at 23:23

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