Convention for writing concentration units

**1st part of my question:**


Q) The concentration of an NaCl solution is 1M. Express this in percent wt. by vol. unit.


Ans:


$$\text{In %(w/v) unit}=\frac{58.5\pu g}{1000\pu{mL}}\times \frac{100}{100}=5.85\ \pu{\%(w/v)}\tag{1}$$


$$\text{In (w/v)% unit}=\frac{58.5\pu g}{1000\pu{mL}}\times \frac{100}{100}=5.85\ \pu{\%(w/v)}\tag{2}$$


**2nd part of my question:**


Q) The concentration of an NaCl solution is 1M. Express this in ppm unit.


Ans:


$$\text{In ppm(w/v) unit}=\frac{58500\pu{mg}}{1\pu{L}}=58500\ \pu{ppm}\tag{3}$$


$$\text{In (w/v)ppm unit}=\frac{58500\pu{mg}}{1\pu{L}}=58500\ \pu{ppm}\tag{4}$$


**My questions:**


1. Which of $(1)$ and $(2)$ is correct?
2. Also, the unit of molarity is $\pu M$, or the unit of mass is $\pu {kg}$. Similarly, what is the unit in the first part of my question? Is it $\text{%(w/v)}$? Is $\text{%(w/v)}$ a unit just like $\pu{kg}$ and $\pu{M}$?
3. Which of $(3)$ and $(4)$ is correct?
4. Also, is it okay if I append/suffix (w/v) at the end of ppm? For example, if I say the concentration of NaCl is $58500\ \pu{ppm(w/v)}$ instead of saying that the concentration of NaCl is $58500\ \pu{ppm}$, will it be okay?




None of the notations, ppm (w/v) or (w/v) ppm, is a standard notation. I don't see this used much in analytical chemistry publications. Very rarely, you might see ppm (w/v) in some papers. If you are doing your own calculations, or writing a report, one should clearly explain how you are expressing concentrations. The extra label (w/v) is not needed because it is understood that for *aqueous* solutions it will be w/v (for convenience). For water, ppm by w/v and ppm by w/w are almost identical.
The mg/ L approximation for ppm does not apply very well to solutions whose density is significantly different from 1. One should be careful about it.


The International Union of Pure and Applied Chemistry book '"Quantities, Units and Symbols in Physical Chemistry" says



> 
> "**Deprecated usage** Adding extra labels to ppm and similar symbols,
> such as ppmv (meaning ppm by volume) should be avoided. Qualifying
> labels may be added to symbols for physical quantities, but never to
> units.
> 
> 
> 


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