# What is the meaning of cmmol in chemistry?

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

• I guess it simply lack space between C and m - it's concentration in mmol per dm3 – Mithoron May 10 '15 at 14:35
• Can you give us more context? Copy and paste here the paragraph where you found it. – Nicolau Saker Neto May 10 '15 at 14:59
• @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 – chemkatku May 11 '15 at 4:10
• 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 ($\rm{1\ cmol} = \rm{10\ mmol}$). – Nicolau Saker Neto May 11 '15 at 14:33
• @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'. – chemkatku May 11 '15 at 15:11

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

• Do you mean that $C\,mmol\,dm^{-3}$ refers to milli moles of charge per litre ? – chemkatku May 11 '15 at 4:07
• @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). – ringo May 11 '15 at 7:41
• 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. – Molx May 11 '15 at 14:00
• Also, the reference given uses lower case $\mathrm{c}$ and not $\mathrm{C}$, which is another point against the Coulomb thing. – Molx May 11 '15 at 14:00
• OK I changed Cmmol to cmmol. My bad, the original text mentions $cmmol\,dm^{-3}$ with a simple 'c' – chemkatku May 11 '15 at 15:08

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