# pH value of HF, hydrogen fluoride or hydrofluoric acid?

I've been looking for a source but I find different results when I try looking for an answer to this. I'm looking for weight percentages of 1 to 10% HF (~0.5 to ~5.1M) and what their pH values are. Now Honeywell says that around 5 to 10% it's pH is above 4.4 However if you calculate this using the $K_a$ of $6.8\times 10^{-4}$, you would get about 1.5 pH, which is quite the difference. http://www3.imperial.ac.uk/pls/portallive/docs/1/7276108.PDF (Honeywell / imperial university) This is just an example, because looking for these values online, for the same molar concentration, different answers are given of around pH 1 to 4.5.

So my question is can somebody explain how to properly get the correct pH values, or confirm what they are.

Also, secondary I would like to create a buffer solution with HF having a pH within the range of 4-7 (specific etching chemistry, $\ce{SiO2}$ vs $\ce{HfO2}$, not etching $\ce{HfO2}$). So other options to achieve this from stock $\ce{HF}$ (49%) with standard chemicals is also an option, however $\ce{NaF}$ is not readily available for me (mostly only access to solutions, such as $\ce{NH4OH}$).

• Not directly pertinent to the question proposed, however...Simply would like to point out that if you do not know what you are doing/are not comfortable handling, HF can be VERY dangerous so please ensure you have the proper protective equipment [for example, simply inhaling a small amount can destroy your vocal cords...] May 22, 2018 at 14:05
• I very well know how to work with HF, we have all the facilities, there's just a bunch of different values regarding pH to be found (a value usually not necessary to know when working with HF). I need a confirmation May 22, 2018 at 14:24
• Sure, I didn't mean any disrespect, just wanted to make sure. May 22, 2018 at 14:54
• @H.Khan - Never apologize for bring up safety. It isn't discussed enough here. HF is a very very nasty chemical.
– MaxW
May 22, 2018 at 16:21
• @H. Khan, Don't worry I understand that you meant well. I just wouldn't be working with it if I was not safe. I talked with the supervisor to get some pH indicators, because we're not allowed to bring in stuff that can tear. He had some special ones left so I was able to use those. May 22, 2018 at 16:25

• All the calculations based on a value for the $K_a$ of HF acid assume that the concentrations equal the activity of the species. For dilute solutions that is fine. For 5 molar solutions the assumption isn't so good.