[metal36]

One desirable (but not always strictly necessary) quality of a mouthwash is that it not be acidic since that may contribute to enamel erosion. A mouthwash I have found very beneficial in my own case is a saturated solution of NaCl.  Today for the first time in my life I had a dental cleaning that was virtually painless and I am sure this is the reason why.  I was recently surprised however to read a dentist recommend against salt solutions because they are acidic.  I thought that couldn't be right.  Then I made my own saturated solution of NaCl and measured the pH with a swimming pool chemistry kit.  It measured as a pretty obvious 7.5 according to the color chart.  This also surprised me.  I know the tap water I start with has a pH below 7, so I was surprised to see salt apparently make it go up.  In medicine saline solutions for IV infusion are known to be acidic (http://www.medsci.org/v10p0747.htm).  Most of the reasons why seem to be negligible, with the most relevant reason being the CO2 absorbed from the air.  And again I presume that this is to a lesser extent the cause of tap water having pH less than 7, though perhaps not as low as distilled water.  In my pursuit of not eroding my enamel, I have three questions to kindly ask if it is not too time-consuming:

Question #1:
Which of the following are true (possibly multiple)?:

a)  NaCl raised the pH of the tap water and I am just ignorant as to why.
b)  The pH reading I took of the salt solution is unreliable for some reason, as maybe it wasn't designed to accurately measure in this context. 
c) 7.5 is the pH of my tap water and I must have messed up earlier readings that said it was below 7, and salt has not altered the pH of the tap water.
d)  The solution is acidic, but no more acidic than tap water is, and salt has not significantly altered the pH of the tap water, and hence I should be no more afraid of eroding my enamel with saturated NaCl than I would be by rinsing my mouth with tap water after I eat. 
e)  The solution is acidic, moreso than tap water, and I am just ignorant as to why. 
f)  Other.

I am inclined to think the answers are B and D.  Assuming that is true (I hope?...), I have a follow up question. 

Question #2:

Essential oils are ingredients in some mouthwashes.  They are first dissolved in alcohol or vinegar, and then can be diluted any amount with water.  I am considering enriching the antibacterial activity of a salt solution with some essential oils in this way.  When I am calculating the pH of a mixture of vinegar/alcohol and salt solution, will it lead to the correct calculation if I consider the salt water portion as if it were just plain water, since the salt should be inconsequential to the result?  And if so, do I consider plain water as having a pH of 7 (like it always was in textbook examples) or as having a pH that I have measured, potentially coming out as low as 5.65 as described in the above paper?  I would think I should use my real-world measurement, right?

Question #3

Would adding sodium bicarbonate be able to raise the pH above 7?  I have read that after a few days sodium bicarbonate in water becomes sodium carbonate which is also basic.  But if salt is already there, I believe the reaction would immediately make sodium carbonate:
NaHCO3 + NaCl -> Na2CO3 + HCl
Does baking soda in this case still effect an increase in pH? 


Thanks!  I never studied chemistry after high school.  I hope parts of my question aren't nonsensical or too rudimentary.  You can understand that the gist of my question is that I want to make a mouthwash that is ideally at least the pH of tap water (or better yet at least pH 7) and still manages to contain the antibacterial benefits of salt and essential oils. 

[Borek]

NaCl solution should be neutral, but almost never is, as the pH depends on the presence of other ions. If you start with the DI water, solution will be slightly acidic as it quickly absorbs CO₂ from the air. If you start with tap water, your solution has a pH of the tap water, which can be anything (as long as it is in the range defined by local regulations about water quality).

Please note per forum rules we don't help in preparation of drugs/cosmetics.

Would adding sodium bicarbonate be able to raise the pH above 7?  I have read that after a few days sodium bicarbonate in water becomes sodium carbonate which is also basic.  But if salt is already there, I believe the reaction would immediately make sodium carbonate:
NaHCO3 + NaCl -> Na2CO3 + HCl
Does baking soda in this case still effect an increase in pH?

It doesn't work this way, pH of the mixture won't change (well, it will change because of the changed ionic strength of the solution, but not by much). But even if the reaction you wrote was correct the net effect would be lowering of the pH, as you listed HCl (a strong acid) between products.