pH notation in text

When referring to units of pH in continuous text (i.e. not in a table), which is the recommended usage?


* pH 7 to pH 8
* pH 7 to 8


What about when the term "pH" has already been mentioned in the text?


* the pH was increased from 7 to 8
* the pH was increased from pH 7 to 8
* the pH was increased from pH 7 to pH 8
* the pH value was increased from 7 to 8




E.g. in the ACS style guide, 3rd edition, rather only the pH symbol itself is focused on, with some examples of “half intervals” ([or how to name that?](https://math.stackexchange.com/questions/3709831/whe-is-a-term-for-half-interval)) notation:



> 
> … Use roman type for pH and pOH; always use lowercase for “p”; always capitalize “H” and “OH”.
> 
> 
>  Solutions were titrated to pH >11.
> 
> 
>  The UV spectra were measured at pH 6.
> 
> 
>  A pOH of <12 was acceptable.
> 
> 
> 


I couldn't find any explicit recommendation for notation of pH ranges. In [*Measurement of pH. Definition, Standards, and Procedures* (IUPAC Recommendations 2002)](https://doi.org/10.1351/pac200274112169) several “notations” are used in text, e.g.


at p. 2179 (11 of 32):



> 
> … between pH 3 and 10 …
> 
> 
> 


p. 2184 (16):



> 
> … pH(S) values of … are in the range 3 ≤ pH(S) ≤ 11 …
> 
> 
> 


p. 2199 (31)



> 
> … in the pH range 3−10 …
> 
> 
> 


 3

**pH 7**


The usage is inconsistent with pH being a dimensionless quantity. It would be logical to write "the pH is 7", or "the pH is in the range from 5 to 8". This would correspond to the symbolic notation:


$$\mathrm{pH} = 7$$
$$\mathrm{pH} = [5,8]\quad \text{ or }\quad 5 < \mathrm{pH} < 8$$


where [5,8] indicates a range.


Instead, usage like "at pH 5" are common and sanctioned by the ACS style guide. It's a bit like saying "I am looking for size 11 shoes" instead of "The size of my shoes is 11".


**pH 7 to 8**


When giving a range of pH values, there is no reason to repeat pH. pH is the quantity, and it is clear that you are giving a range for that quantity. This is different from giving a range of lengths, or a length with a standard deviation. In that case, both lengths, or the length and its standard deviation need to have units, e.g.


$$l\_1 = \pu{2.3 cm}\ ..\ \pu{2.4 cm}$$


$$l\_2 = \pu{21.7 cm} \pm \pu{0.3 cm}$$


Of course, you can leave out the duplicated unit by using parentheses:


$$l\_1 = (\pu{2.3}\ ..\ \pu{2.4})\pu{cm}$$


$$l\_2 = (21.7 \pm 0.3)\pu{cm}$$


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