8
$\begingroup$

I came across a unit called $\text{cmmol dm}^{-3}$ in buffer solutions. What does this unit mean?

$\endgroup$
  • 1
    $\begingroup$ I guess it simply lack space between C and m - it's concentration in mmol per dm3 $\endgroup$ – Mithoron May 10 '15 at 14:35
  • 1
    $\begingroup$ Can you give us more context? Copy and paste here the paragraph where you found it. $\endgroup$ – Nicolau Saker Neto May 10 '15 at 14:59
  • $\begingroup$ @NicolauSakerNeto: I'm sorry can't paste it because it was a handwritten one. But I've found some other references online. Such as thenakedscientists.com/forum/index.php?topic=35027.0 and labfert.agr.br/ferramentas.php $\endgroup$ – chemkatku May 11 '15 at 4:10
  • $\begingroup$ That first reference doesn't seem clear to me, and the second one uses $\rm{cmol}$ rather than $\rm{Cmmol}$, in which case it simply means centimol, i.e. a hundredth of a mole ($\rm{1\ cmol} = \rm{10\ mmol}$). $\endgroup$ – Nicolau Saker Neto May 11 '15 at 14:33
  • 1
    $\begingroup$ @NicolauSakerNeto I agree that the references are not relevant. The original text I referred mentions $cmmol\,dm^{-3}$ and not $cmol\,dm^{-3}$. And I have changed 'C' into 'c'. $\endgroup$ – chemkatku May 11 '15 at 15:11
6
$\begingroup$

Upon researching this, I found that this a measurement of charge:

$$\mathrm{cmol=10~\mathrm{meq}}$$

and

$$1~\mathrm{eq}= \mathrm{F}$$

where $\mathrm{F}$ is Faraday's constant and is:

$$\mathrm{F}=96 485.3365~\mathrm{C}$$

So:

$$\mathrm{cmmol}=\frac{\mathrm{cmol}}{1000}=\frac{\mathrm{eq}}{100000}=.96 4853365~\mathrm{C}$$

Sources:

http://en.wikipedia.org/wiki/Equivalent_%28chemistry%29

https://www.agronomy.org/files/publications/jnrlse/pdfs/jnr014/014-02-0084.pdf

$\endgroup$
  • $\begingroup$ Do you mean that $C\,mmol\,dm^{-3}$ refers to milli moles of charge per litre ? $\endgroup$ – chemkatku May 11 '15 at 4:07
  • $\begingroup$ @chemkatku actually, since Faraday's number is 1 mole of charge, which is equal to 1 equivalent, $1~\mathrm{cmmol}~\mathrm{dm^{-3}}$ is 10 micro moles of charge (per liter). $\endgroup$ – ringo May 11 '15 at 7:41
  • 2
    $\begingroup$ Do you have any reference to back this up? One mole is similar but not the same as one equivalent, and I've never heard anything relating $\mathrm{eq}$ with $\mathrm{F}$. I agree with @Mithoron and I think this is simply a typo. It was supposed to be either $\mathrm{cmol}$ or $\mathrm{mmol}$ (or the $\mathrm{C}$ is from concentration and a space is missing) per $\mathrm{dm^{-3}}$, which is a litter, and this sounds a lot like a buffer concentration, which in turn can be related to it's "capacity" as the full question mentions on the link provided above. $\endgroup$ – Molx May 11 '15 at 14:00
  • 1
    $\begingroup$ Also, the reference given uses lower case $\mathrm{c}$ and not $\mathrm{C}$, which is another point against the Coulomb thing. $\endgroup$ – Molx May 11 '15 at 14:00
  • 1
    $\begingroup$ OK I changed Cmmol to cmmol. My bad, the original text mentions $cmmol\,dm^{-3}$ with a simple 'c' $\endgroup$ – chemkatku May 11 '15 at 15:08
2
$\begingroup$

The unit $cmmol\,dm^{-3}$ is the same as $mmol_{c}\,dm^{-3}$ which denotes the millimoles of charge per litre. I think the former notation is not well used anymore. On the other hand, latter is used often and a google search would return a number of references. For example,

http://micromaintain.ucanr.edu/Prediction/Source/Groundwater/Potential_for_clogging/CP/Water_analysis_for_hazard/Levels_of_concern/

http://www.slidefinder.net/c/converting_various_units_mmol_mmolc/32208520

http://www.scielo.br/scielo.php?pid=S0103-90162011000400012&script=sci_arttext

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.