Qed
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Hydroflouric acid solution...
I am new to this and I have been asked to make a 12 molar hydroflouric solution. What are the ratios that I can use to attain that solution?
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woelen
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What are your starting materials? If you start from anhydrous HF and water, then this is a simple problem.
Simply take 12 mol of HF, which is 12*20 = 240 grams of HF. Using a table for density you can find how many ml of HF this is. Then add water (while
mixing constantly), until the volume is 1 liter.
I really hope that you are not planning to do this in reality. HF is intensely poisonous and fantastically dangerous. Acids like HCl and HNO3 are
children's toys compared to HF.
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Qed
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The Hydroflouric acid is a 48-51% solution in water. I will be doing this at work with the proper PPE and under a fume hood. Just getting
clarification as to the ratios that I should use for reassurance.
The fact that the HF is in a 48-51% solution, does that change the ratios that much?
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Eclectic
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If you don't know enough chemistry and math to work this out on your own, you REALLY should not be working with HF. This is a beginning high school
chemistry level question.
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woelen
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I do not know the density of appr. 50% HF, but let's assume it is not too much away from 1 g/ml. Then a mix of 1 part of this 50% acid and 1 part of
water will be quite close to 12 M. Maybe a tad too high. For more precise math, lookup the density of your solution and the precise percentage, then
you can compute which volume is needed for 12 mol of HF (and I expect that to be something just below half a liter) and then you add water till a
volume of 1 liter is obtained.
Of course you can scale up or down my computation, the math for that is for you.
But I agree with Eclectic. The fact that you ask this simple question does not give us the impression that you should work with HF.
[Edited on 10-5-07 by woelen]
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chromium
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According to one russian chemistry handbook 50% HF has density 1.155 g/cm3 and contains 577.5g or 28.86 mol of HF per 1000 ml solution.
Remember to be be very carefull as even minor skin contact can kill you!
When all think alike, then no one is thinking. - Walter Lippmann
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Qed
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Chromium,
I want to thank you for your information. To all, I know that HF is very dangerous. The MSDS and common sense are good indicators for it.
As for not belonging here or working with such chemicals because my question is general high school chemistry... I guess I will have to go back to
my notebooks from 1990? I haven't dealt with much chemistry (and even with my new job, it's a rare occasion that I deal with such materials).
I came to this board looking for some assistance. Thank you Woelen and Chromium. I guess I will have to start hitting the books again.
[Edited on 10-5-2007 by Qed]
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not_important
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I'm going to suggest reading the following threads, previous discussions on working with hydrofluoric acid
http://www.sciencemadness.org/talk/viewthread.php?tid=6261&a...
http://www.sciencemadness.org/talk/viewthread.php?tid=5070&a...
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Eclectic
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I think everyone here just wants to make sure you don't get the next Darwin award. Make sure you have calcium gluconate on hand, heavy long rubber
gloves, lab apron, rubber boots, ect.
Treat HF the same way you would Prussic Acid (hydrogen cyanide).
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Qed
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Eclectic, Appreciate the concern. That is why I was in here asking questions and reviewing the MSDS et al. I am not one to smear and smell
something to find out what it is. I am also in the process of purchasing more and (in my opinion) more effective PPE than my place of work currently
has. The pitfalls of working for a start up company.
Not_important, THANK YOU for the thread links. very informative reads. I will arrange to receive some Calcium Gluconate for the saline solution
mentioned in the threads.
Learning more and more every day!
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dedalus
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Once upon a time, I built an ozone generator. The first step was to etch a piece of glass tubing with HF.
I brushed it on with a paintbrush, while it was in a basin. I used an air purifying respirator, PVC gloves, sleeve protectors, and a Tyvek lab coat.
I was shitting with fright handling this stuff.
Make sure to have lime slurry handy to neutralize spills. If you get it on you, go to the hospital without delay to get the exposed
area injected with calcium gluconate solution.
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Pyridinium
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I was searching around for useful density tables (CRC Handbook doesn't have HF) and found something called Chembuddy. I think I remember one of the
people on this board having something to do w/ that program. Anyway it looks like a handy source of data for exactly the kind of thing you're trying
to calculate, Qed.
I'd rather work with prussic acid than HF. With prussic, either you pass out and wake back up, or you just don't wake up. 
I understand some suppliers sell HF in a bottle that has a special indicator in the wrapper, so you can know at a glance if HF drops are on the
outside. With HF that's a nice thing to know.
Back to the problem. Supposing you have 48-51% HF, it would be nice to titrate some or measure the density so you could peg that number at a more
definite value. You'd need that to end up with a known molarity when making a dilution. Unless, of course, you only need "roughly" 12 Molar. Or
unless your lot of HF has a cert. of analysis for that lot, and you know it hasn't been left uncapped in a hot place.
Concentrated HF is typically 16 to 16.5 Molar. If you could peg this at some definite value, you could easily make up a dilution to 12 molar. As I
said, it would help to make sure what the initial conc. really was. So, titration or precise measure of the intial density. Though if I had to do
it, I'd want a full protective suit of sheer rubber, like the guys who load tanker trucks of acid sometimes wear.
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woelen
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| Quote: | Originally posted by chromium
According to one russian chemistry handbook 50% HF has density 1.155 g/cm3 and contains 577.5g or 28.86 mol of HF per 1000 ml solution.
Remember to be be very carefull as even minor skin contact can kill you! |
OK, then making a 12 M solution is easy by now.
I describe how to make one liter. This procedure can easily be scaled up by multiplying all volumes with the same factor.
You need 12 mol of HF, this is 12/28.86 liter of 50% solution, which is 416 ml. To this, slowly add water (while mixing frequently), until the total
volume is 1 liter. Simply adding 600 ml will give you roughly 12 M solution. If you want it more precise, then you need to add water, until the final
volume becomes 1 liter.
The latter is needed, because you cannot simply add volumes when two different liquids are mixed. The mixed liquid may contract or expand (usally
contract, but there are a few exceptions) a little and so by adding the two liquids to each other the total volume after good mixing may differ quite
noticeably from the sum of the two volumes.
All the above is some theory, but not the practical thing: If you want quick and simple work without too much hassle then take 400 ml of acid and 600
ml of water and mix. Good enough for most purposes which call for roughly 12 M I think. Better than this you can't achieve anyway if the concentration
is not known more precisely than being between 48% and 51%.
[Edited on 11-5-07 by woelen]
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