[mudassir]

@mudassir
Actually, my question was more for the persons helping you, but your input does help me understand

did you rinse them again with water after you applied the caustic soda?

Sorry Bill, I'm not intended to misguide. I'm not a chemist at-all and any input from an expert chemist will be much more important than mine. I only did a little experiment with the lowest degree of HF (40).

Dipped 3mm & 2mm glass sheets in the solution for 3-4 minutes, rinse them with fresh running water two-three times. And for extra safety, I washed my sheets with caustic soda and rinsed them in running water once again.

** But the solution, HF(40), I used was not pure HF at-all, it was slightly yellow and positively it was mixed with sulfuric acid or something similar.

Once again, I declare that I am not a chemist and any input from Arkcon will be much more important. I advice any viewer not to follow my experiment or advice. I'm working with HF for the very first time and want no injury. HF is highly dangerous.

[billnotgatez]

I changed my post slightly while you were putting together your answer, but you still came out with the correct response.
thank you

Now we wait for others to respond

[Arkcon]

Lots happening here:  OK, here's some points:

HF comes in a variety of concentrations, like many acids.  Try to realize that HF, like HCl, are gases, so 100% active is supplied in a compressed gas tank, and that is impractical for most applications.  If 40% gives adequate results, then go with that, instead of buying a more concentrated solution.  That's just good lab practice -- not buying more volume or more concentrated reagent than you need.

We bought cases of 1 N NaOH in 1 L bottles for other uses, for example, adjusting the pH of a prepared HPLC eluent.  Its not too expensive, comes in a handy, easy pour plastic bottle, is guaranteed at the proper concentration (within its expiration date,) and we don't have to mix it ourselves from solid NaOH.  (We would have used the formula weight to mass out the correct grams per liter and mix it with water.  And chemist or not, we will expect you to learn the method yourself on this board mudassir:, so that you don't ask the same question multiple times, and develop the knowledge for yourself to be certain you're doing it properly.)

The HF arrived in small, 100 ml bottles (it was actually HF.3TEA for cleaving off silyl protecting groups.)  When the bottle was used up, we rinsed out adhering droplets by filling it with 1 N NaOH, and dumped the filled bottle into HF waste.  We also rinsed ou pipette tips with 1 N NaOH before we disposed of them.  We were certain therefore that we had used great excess of NaOH, so that the "HF waste" surely contained no HF, but instead NaOH and some NaF.  Note:  this NaF can no longer eat through skin and bone, and unlike HF no longer a gas, but if ingested can still kill a living thing.  We stored this waste separately, and the waste handler took it separate from other wastes.  (You realize, if the NaF plus NaOH waste is mixed with great excess of other acid waste, you get HF solution and vapor back.)

If you have a vat full of left over 40% HF solution, you will need lots of NaOH.  Maybe in that case, it would be better to buy the pellets, prepare a stronger solution, and mix.  You will get heat from this reaction, and that will send more HF vapor out as the neutralization proceeds.  This is why I wouldn't use bicarbonate or carbonate, those chemicals are safer alone than NaOH is, but they release gas when they neutralize an acid, and you don't want foaming half-neutralized HF.  Likewise, you my not want to buy NaOH pellets and drop some in, although that would be the most efficient way to neutralize acid.  You might get too much heat.

Anyway, if you examine your neutralized solution with pH paper, and it is definitely alkaline because you've added great excess of base, you're golden, that is just NaF plus NaOH waste.  This can be a bit tricky.  My boss related an anecdote, he "thought" he had quenched an HF reaction, presumably made it neutral, then stored the waste in a flask in the hood over the weekend, and came back to a flask with no bottom.  Note that a great excess of NaOH means that this solution, now no longer HF is now essentially a strong NaOH solution, and that's not perfectly "safe" to handle.  Hence my joke above how I've made the solution "safe" by using an excess of base.  And why its important to rinse the NaOH.

[mudassir]

Some folks are selling "Ammonium Bi-Fluoride (powder)" as a "safer alternate" to HF for etching glass. They call it acid-free glass etching solution. A mixture of NH4HF2/NH4F·HF and water is also a good etchant for glass. An estimated ratio for the solution can be:

NH4HF2 : H2O --> 1 : 0.2  or  1 : 0.4

But Ammonium Bi-Fluoride is a weak acid salt of HF. Now, the next series of questions is:

1. How safer will it be to use NH4HF2 + H2O solution while compared to using HF?
2. What will be reaction when mixing NH4HF2 with water?

[Arkcon]

If you can use ammonium bifluoride or potassium bifluoride, you may find them safer.  A little checking on the MSDS online tells me its just as toxic, but they might not attack flesh and bone as readily, the MSDS for these substances don't mention the serious medical support that HF exposure does.  You might get a different sort of etch pattern, or it might take longer.

http://www.sciencestuff.com/msds/C1208.html