" the acidity of HF solution? " What solutions, aqueous? If in organic solvent, then which solvents. What is the acidity?

Be very specific when asking questions.

Interesting, following.

Dr. Yurii V Geletii , thank you very much for your comment.

I have added the detailed information of my solutions. Since I am not a chemist, there is such kind of basic question.

What kind of glass do you have as your glassware?

Dr. Yurii V Geletii , I employed a Teflon Beaker for the solutions. I found that the pH checkers usually have a glass part, so I am going to use pH test papers. Are the papers reliable for non-aqueous based solutions?

I am going to use this paper:

https://axel-search-e.as-1.co.jp/asone/global/d/2-345-08/?cfrom=B0030200

The pH paper strips are designed only for aqueous solutions and they give very approximate pH value. Your task is a very complex even for highly professional chemist. I'm not sure that I would be able to solve your problem. You are not a chemist and would need to learn too much just to get some ideas about the complexity of your question.

When it comes to acidity, I first think about activity of H+ in solution (Bronsted theory). Here, pH measurement is suitable. Because solution contains HF, a normal pH meter is not recommended. Since methanol can be mixed with water with any proportion to form a homogeneous solution. So you can simply assume it is aqueous even at high ratio of methanol (not so sure). Then simply check pH by pH test paper.

As Dr. Yurii V Geletii said, the pH paper strips are designed only for aqueous solutions and they give very approximate pH value. You should be noticed with this.

I hope it helps.

"So you can simply assume it is aqueous even at high ratio of methanol (not so sure)" is not correct. pH test papers are applicable only in aqueous solutions.

The pH depends on thermodynamics of autoionization of methanol + water mixtures.

Read on autoionization of methanol + water mixtures:

10.1039/F19726800523

J. Chem. Soc., Faraday Trans. 1, 1972,68, 523-532

@Yurii V Geletii: You are right. I have no idea of how to measure precisely pH in this case. I cannot access the article. Could you please briefly teach me effect of methanol in this measurement?

I've sent you the paper. As I wrote, this is a very complex area. In order to teach you I must learn much as well. This would a full research project for me. Sorry, Yurii

I have a good way to measure acidity.

The HF could be replaced by a little of HClO4. Then an amount of methyl red was added to the above solution. We assume that all perchloric acid is ionized. Then we can calculate hydrogen ion concentration. A series of solutions with different acidities were used to measure UV-VIS spectra, in order to obtain the pH-Intensity relationship. The sample solution was also measured by using the same method. At last, the acidity of the sample solution could be evaluated by the obtained pH-intensity curves.

Dear Tao Sha,

Your protocol would not work. I know well the theory behind the use of pH indicators. It's not as simple as you think.

Dear Lipeng Xin,

If you recommend the question, You have to be sure that the answer is correct from your point of view.

Yurii V Geletii Thank you very much for paper. It is good chance to learn.