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I am a physician and administer 0.9% NaCl in water ("normal saline") to patients frequently. The bag says it has a pH of 5.5 (compared to the human body of 7.4).

I am asking why the pH is so low. It is because NaCl is the salt of HCl? I read on wikipedia that the pH of NaCl aqueous solutions is 7. I teach medical students and want to give an understandable explanation why the pH on a bag of "normal saline" reads pH 5.5 and when we give lots of saline to patients, they develop acidosis in the blood.

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    $\begingroup$ There is an entire article dedicated to this topic, actually:) $\endgroup$
    – andselisk ♦
    Jan 3 '18 at 22:39
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    $\begingroup$ Wow. Thank you for the super fast replies!!! That is awesome. I will go through the article you linked and see what it has to say. Much appreciated. $\endgroup$
    – Jason
    Jan 3 '18 at 22:45
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    $\begingroup$ It would seem that a normal saline solution isn't buffered at pH 5.5. Thus there is really very little acid in an absolute sense. A typical carbonated beverage would have thousands of times more acid. $\endgroup$
    – MaxW
    Jan 3 '18 at 23:33
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    $\begingroup$ Check this article: ncbi.nlm.nih.gov/pmc/articles/PMC3638298 Saline (0.9% salt solution) seems to be a beast to measure its pH, but harmless to the patients. $\endgroup$
    – user91823
    Apr 7 '20 at 14:58
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Medical saline has a $\mathrm{pH}$ of 5.5 do to the dissolved $\ce{CO2}$ within the solution as well as factoring in the degradation of the PVC packaging.

I reference the attached article from the International Journal of Medical Sciences from 2013:

Benjamin AJ Reddi, “Why Is Saline So Acidic (and Does It Really Matter?),” Int. J. Med. Sci. 2013, 10(6), 747-750 (doi:10.7150/ijms.5868)(PDF).

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