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Author: Subject: Pressure Vessel
International Hazard

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shocked.gif posted on 26-4-2021 at 12:06
Pressure Vessel

How can I tell how much reagent to add, of Red Phosphorus, and I2, to make enough pressure but not too much pressure?

I'm wanting to make the hydroiodic acid,(HI) but I'm not sure, how much of reagents in a 2:1:.85 ratio of RP:I2:H2O ...

Not sure how much pressure say a combined total of 3.85 g of the mixture will create, is this a combined gas law problem?

Also, when distilling a mixture, is it necessary to distill to dryness to get all of the fractions and have a mixture in the recieving flask with the same composition as the original mixture? (Minus the dye)

I've heard distilling to dryness is bad, why is this?

And can someone explain how the azeotrope of rubbing alcohol works?

What kind of azeotrope,
Does it remove water when boiled only at higher concentrations of the iso to water?

Iirc, as iso alcohol boils (low alcohol conc) -- the solution gets dryer, alcohol and water boil away until there is very little water, at which point the alcohol will be concentrated and it will remove much more H20.

[Edited on 4/27/2021 by Yttrium2]
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26-4-2021 at 13:37

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[*] posted on 28-4-2021 at 16:42

Hydrogen iodide is a gas, and therefore it follows the Clausius–Clapeyron relation, pV = nRT. You could calculate the pressure if you knew the quantity of HI that would be produced, and ignore the fact that HI is soluble in water.Of course, the equation contains the T term, which makes the pressure vary depending on the temperature - be aware, though, that if the conditions inside the vessel allow the solvent (water) to evaporate, you will be suddenly dealing with much more moles of gas, which means substantiouly higher pressure. You probably shouldn't be playing with pressurised reactos at home, because what you might end up with is basically a pipe bomb.

Distilling to dryness is not a good practice, because at the very end of the distillation what's left in the boiling flask is going to decompose thermally, producing impurities, since there's no more low-boiling solvent to keep the temperature from rising. There are instances when distilling to dryness can make you lose a finger or two - read about the formation of diethyl peroxide in ethyl ether and it's energetic properties.

Isopropyl alcohol forms an azeotrope with water at 87.7% concentration, wich (overly simplified) means that is what the maximum proportion of iso to water is going to be in the vapors you get into the condenser. If you start from for ex. 70% isopropyl in water, you'll distill off the iso first, but there's always this 12.3% of water that's gonna get distilled along.

If you start with anhydrous isopropanol and carry out a reaction that results in water forming, any small amount of water produced is gonna get in the vapour phase (because the isopropanol vapour really w a n t s to form this azeotrope of 87.7%, so it pulls all the water it can from the liquid phase). You won't get dryer and dryer iso if the concentration is below 87.7% though, you'll just boil off the mixture, leaving water in the boiling flask (and getting max. 87.7% iso in the recieving flask).
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International Hazard

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[*] posted on 29-4-2021 at 03:36

Three Questions at once?

Making HI shouldn't require Red Phosphorus, and it shouldn't require pressure.
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[*] posted on 29-4-2021 at 21:21

This whole thing looks like the results you'd get if you googled "how to make me*h." Not that I've done that, but just reading about why phosphorus and iodine are banned, that it has something to do with hydroiodic acid, etc. Not that that's the only reason to do this, although yttrium2 has had a bunch of posts about aderall, etc. I still can't say this is what he's after with any certainty. It also looks like the results of hearing a rough outline of a concept, with a few procedural details dropped in, and no big-picture explanation of why it works like that.

Okay, what's "enough pressure but not too much." 1 atmosphere but not 2? 5 MPa but not 7? This is like asking what's the right length for a string without telling us what you're using it for.

[Quote]"Also, when distilling a mixture, is it necessary to distill to dryness to get all of the fractions and have a mixture in the recieving flask with the same composition as the original mixture? [/Quote]

That would defeat the purpose of distilling. Again, whether it's just the dye left or if there's other non volatiles depends on the composition and temperature involved.

Yttrium2, Konduktor, has it ever occurred to either of you that Hydrogen Iodide might be soluble in water? Or that it might be able to liquify at room temperature with sufficient pressure?

[Edited on 30-4-2021 by Vomaturge]

I now have a YouTube channel. So far just electronics and basic High Voltage experimentation, but I'll hopefully have some chemistry videos soon.
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