In class, the other day, we were discussing pH curves. Assume that I have HCl and NaOH of concentration 1 mol/mL. Now, consider that I have 50mL of HCl, and begin adding small quantities of NaOH. I observe that the pH increases, and once the volume added of NaOH reaches 50mL, the pH of the resulting solution becomes 7.
However, when mathematically calculating, if I added 49.99999 mL of NaOH, I find that the pH is way over 7 (the concentration of H+ becomes 50-49.99999 divided by 99.99999), which seems to be an anomaly. In essence, when finding the limit of - log (H+) as [H+] approaches 0, it needs to equal 7, but it doesn't. Does this mean that there should be a horizontal asymptote at pH = 7? Can somebody please explain this?