# Why does saline have a pH of 5.5?

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.

• There is an entire article dedicated to this topic, actually:) – andselisk Jan 3 '18 at 22:39
• 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. – Jason Jan 3 '18 at 22:45
• 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. – MaxW Jan 3 '18 at 23:33
• 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. – user91823 Apr 7 at 14:58

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.