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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 $\ce{NH4OH}$).

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    $\begingroup$ 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...] $\endgroup$ – H. Khan May 22 '18 at 14:05
  • $\begingroup$ 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 $\endgroup$ – Bob van de Voort May 22 '18 at 14:24
  • $\begingroup$ Sure, I didn't mean any disrespect, just wanted to make sure. $\endgroup$ – H. Khan May 22 '18 at 14:54
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    $\begingroup$ @H.Khan - Never apologize for bring up safety. It isn't discussed enough here. HF is a very very nasty chemical. $\endgroup$ – MaxW May 22 '18 at 16:21
  • $\begingroup$ @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. $\endgroup$ – Bob van de Voort May 22 '18 at 16:25
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I was able to get some rough pH indicators that are allowed in our lab (cleanroom environment). No clue why a supplier like Honeywell has completely wrong data.

Apparently some sources are completely off, doing the calculation based -log(1/H+) gives the correct values in the end, tested for 50, 10, 5, 1 and 0.5%. for a quick calculation see: http://www.endmemo.com/chem/phcal.php

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    $\begingroup$ 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. $\endgroup$ – MaxW May 22 '18 at 16:24
  • $\begingroup$ How were the indicators validated? $\endgroup$ – Linear Christmas May 23 '18 at 17:15
  • $\begingroup$ These are special double indicator strips that do not leave particles, but it's still a visual inspection, so it's an approximate answer. mn-net.com/Testpapers/pHTests/DUOTEST/tabid/10472/language/… for pH 1.0 to 4.3, however due to the HF, the range is more like 0.6 or 0.9 even when checking (held above and dipped with teflon tweezers). $\endgroup$ – Bob van de Voort May 23 '18 at 18:24

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