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Thread: HCN Chemistry Question From Wiki.

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    HCN Chemistry Question From Wiki.

    I was looking up, and finally found, the pathway for the production of HCN in the interstellar medium in the wiki article on HCN. All well and good I'm sort of happy with what I found.

    But as I was reading the rest of the article they mention something I think is wrong. When HCN is used for executions, the wiki article says the principle ingredients where sulfuric acid and potassium cyanide.

    I always thought it was hydrochloric acid and potassium cyanide. You know, to produce hydrogen cyanide via simple substitution.

    https://en.wikipedia.org/wiki/Hydrogen_cyanide

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    Each are both, I think. React potassium (or sodium) cyanide with a strong acid, and you'll get HCN(g) evolved, above a solution of the potassium (or sodium) salt of the acid.
    Perhaps there are practicalities involved, but I'm not going to go searching on that one, thanks.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    Each are both, I think. React potassium (or sodium) cyanide with a strong acid, and you'll get HCN(g) evolved, above a solution of the potassium (or sodium) salt of the acid.
    Perhaps there are practicalities involved, but I'm not going to go searching on that one, thanks.

    Grant Hutchison
    That would be my take. Both will produce HCN (g).
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    Oh hey, sorry!

    I was so focused on the chemistry question the "execution" part sort of rolled right passed me.

    Apologies for appearing insensitive.
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    Sulfuric acid seems a poor choice to me. Sure you get two protons instead of one, but even in dilute solution, the stuff will burn holes in your blue jeans.
    The stuff boils at 337 C, so the water evaporates first, leaving small spots of acid concentrated enough to eat cotton.
    HCl boils much lower, so it usually evaporates before forming chemist's pinholes in your nice new pants. Far easier to dispose, HCl's reaction with water is seldom violent enough to make things boil. Concentrated H2SO4 and water get very hot when mixed.

    HCl is a much safer choice in the hands of non-chemists.

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    Quote Originally Posted by Squink View Post
    Sulfuric acid seems a poor choice to me. Sure you get two protons instead of one, but even in dilute solution, the stuff will burn holes in your blue jeans.
    The stuff boils at 337 C, so the water evaporates first, leaving small spots of acid concentrated enough to eat cotton.
    HCl boils much lower, so it usually evaporates before forming chemist's pinholes in your nice new pants. Far easier to dispose, HCl's reaction with water is seldom violent enough to make things boil. Concentrated H2SO4 and water get very hot when mixed.

    HCl is a much safer choice in the hands of non-chemists.
    That higher boiling point means fumes are less of a concern and you don't have to worry about the acid evaporating away and then producing insufficient HCN.

    Sulfuric acid has been widely used in lead acid batteries for over a century. It's not that dangerous.

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    Quote Originally Posted by cjameshuff View Post
    That higher boiling point means fumes are less of a concern and you don't have to worry about the acid evaporating away and then producing insufficient HCN.

    Sulfuric acid has been widely used in lead acid batteries for over a century. It's not that dangerous.
    It is to blue jeans!

    And car batteries have always produced novel medical issues when handled, and then one neglects to wash one's hands before "using the facilities".

    I knew one poor fool who didn't have "the procedure" before hand, and had burned himself so badly by doing the above, that his physicians decided the best way to deal with the sulfuric acid burns was a standard circumcision.

    That poor clown was miserable. Couldn't wear anything but a loose bathrobe for more than a week!

    ({Announcer voice} And all across the astronomy and physics community, male scientists simultaneously crossed their legs at 11:50 AM PDT.)
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    I've no experience of it myself, but I do suspect sulphuric acid will be more efficient than hydrochloric.

    The reaction product of sulphuric acid and KCN is potassium sulphate. The left-overs from HCl + KCN will be a solution of mixed K, Cl and CN. So you have a cyanide containing residue to deal with.

    Also HCl is more quite volatile and the fumes are severely unpleasant. On the other hand there's no fumes to speak of from sulphuric acid at normal temperatures. This execution would be more humane using sulphuric acid compared to HCl.

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    Quote Originally Posted by kzb View Post
    I've no experience of it myself, but I do suspect sulphuric acid will be more efficient than hydrochloric.

    The reaction product of sulphuric acid and KCN is potassium sulphate. The left-overs from HCl + KCN will be a solution of mixed K, Cl and CN. So you have a cyanide containing residue to deal with.

    Also HCl is more quite volatile and the fumes are severely unpleasant. On the other hand there's no fumes to speak of from sulphuric acid at normal temperatures. This execution would be more humane using sulphuric acid compared to HCl.
    Um, the residue wouldn't be an issue. You're already working with potassium cyanide. I'm sure the safe handling requirements would be similar.

    Two, the sulphuric acid is reacting with the potassium cyanide. It wouldn't be at a normal temperature. (I assume you mean room temperature.) Unless the reaction is endothermic? Anyone?

    Three, let's not talk about executions here. A lot of poster have a lot of strong opinions on the matter.
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    Quote Originally Posted by BigDon View Post
    Um, the residue wouldn't be an issue. You're already working with potassium cyanide. I'm sure the safe handling requirements would be similar.

    Two, the sulphuric acid is reacting with the potassium cyanide. It wouldn't be at a normal temperature. (I assume you mean room temperature.) Unless the reaction is endothermic? Anyone?

    Three, let's not talk about executions here. A lot of poster have a lot of strong opinions on the matter.
    It was you who asked about executions, and I was simply responding with what I think could be valid reasons for choosing sulphuric acid over hydrochloric acid. Another one is that HCl fumes are extremely corroding for steel, even stainless steel.

    Yes the reaction is probably exothermic but the boiling point of sulphuric acid is about 300 degrees (C). You won't generate much in the way of sulphuric acid fumes, even at the (much lower) boiling point of hydrochloric acid.

    The "residue" I was referring to may have been misleading terminology on my part. I don't mean a solid residue, I mean an aqueous solution that still contains cyanide after use. This would be hazardous for the staff to handle.

    If I was designing the process from scratch I would probably go with sulphuric acid as first choice acid to use.

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    Quote Originally Posted by kzb View Post
    It was you who asked about executions, and I was simply responding with what I think could be valid reasons for choosing sulphuric acid over hydrochloric acid. Another one is that HCl fumes are extremely corroding for steel, even stainless steel.

    Yes the reaction is probably exothermic but the boiling point of sulphuric acid is about 300 degrees (C). You won't generate much in the way of sulphuric acid fumes, even at the (much lower) boiling point of hydrochloric acid.

    The "residue" I was referring to may have been misleading terminology on my part. I don't mean a solid residue, I mean an aqueous solution that still contains cyanide after use. This would be hazardous for the staff to handle.

    If I was designing the process from scratch I would probably go with sulphuric acid as first choice acid to use.
    Okay, fair enough. You have made your case.

    You give good reasons and obviously I don't know enough chemistry to nay-say you or I wouldn't have had to ask this in the first place.
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    If I was designing from scratch, I'd go with HCl.
    Sulphuric is just too much of a hazard when spilled in tiny quantities.
    Water evaporation just keeps making it stronger and stronger.
    Acetic acid might be an even better choice.

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    Quote Originally Posted by kzb View Post
    I've no experience of it myself, but I do suspect sulphuric acid will be more efficient than hydrochloric.

    The reaction product of sulphuric acid and KCN is potassium sulphate. The left-overs from HCl + KCN will be a solution of mixed K, Cl and CN. So you have a cyanide containing residue to deal with.

    Also HCl is more quite volatile and the fumes are severely unpleasant. On the other hand there's no fumes to speak of from sulphuric acid at normal temperatures. This execution would be more humane using sulphuric acid compared to HCl.
    There'd only be residual KCN if there's insufficient HCl, just like any other acid. The volatility of HCl just means you'd need to use some excess to ensure enough remained in the mixture to react with the KCN. And of course, your HCN is then contaminated with HCl.

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    Quote Originally Posted by Squink View Post
    If I was designing from scratch, I'd go with HCl.
    Sulphuric is just too much of a hazard when spilled in tiny quantities.
    Water evaporation just keeps making it stronger and stronger.
    Acetic acid might be an even better choice.
    Do you know if acetic acid is a strong enough acid?

    Also, the acetic acid fumes are unpleasant.

    The property of sulphuric acid that it gets stronger and stronger as water evaporation proceeds is actually an advantage in this process. By heating the remaining solution you can ensure there is no cyanide whatsoever remaining.

    Hot concentrated sulphuric acid actually destroys cyanide, turning it into carbon monoxide. Although in practice HCN would be volatilised before that point, if starting from dilute sulphuric acid.

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    pKa of KCN runs about 11.0 Acetc acid 4.7.
    The reaction should go nicely.
    My main objections to sulphuric are that It's a pain to clean up, plus it puts out a Lot of heat when added to As solutions.
    I've seen corrosive geysers hit the ceiling when some undergrad trays filling their 500 ml grad cylinder with 200 ml water, then 300 ml sulfuric.
    Hal and acetic don't act that way, yet will produce HUN. Why add risk, when not needed?f

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    Quote Originally Posted by Squink View Post
    pKa of KCN runs about 11.0 Acetc acid 4.7.
    The reaction should go nicely.
    My main objections to sulphuric are that It's a pain to clean up, plus it puts out a Lot of heat when added to As solutions.
    I've seen corrosive geysers hit the ceiling when some undergrad trays filling their 500 ml grad cylinder with 200 ml water, then 300 ml sulfuric.
    Hal and acetic don't act that way, yet will produce HUN. Why add risk, when not needed?f
    We're talking about a reaction for producing HCN gas. Using sulfuric acid is an insignificant contributor to the overall hazard, and people who can't dilute sulfuric acid properly have no business whatsoever performing this reaction. On top of that, trying to clean vapors of other volatile acids out of the product would greatly increase the overall hazard.

    Sulfuric acid is simply not that dangerous, and the reaction does not require it to be highly concentrated...in fact you don't want highly concentrated sulfuric acid because of the side reaction kzb mentioned. Use a small excess so you end up with dilute H2SO4 instead of dilute KCN, then just add a mild base to neutralize that. If you leave the container of dilute sulfuric acid, K2SO4, and residual dissolved/bubbles of HCN sitting there for days to self-concentrate afterward instead of disposing of it properly, you've got problems using another acid won't fix.

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    Quote Originally Posted by Squink View Post
    pKa of KCN runs about 11.0 Acetc acid 4.7.
    The reaction should go nicely.
    My main objections to sulphuric are that It's a pain to clean up, plus it puts out a Lot of heat when added to As solutions.
    I've seen corrosive geysers hit the ceiling when some undergrad trays filling their 500 ml grad cylinder with 200 ml water, then 300 ml sulfuric.
    Hal and acetic don't act that way, yet will produce HUN. Why add risk, when not needed?f
    This is beside the point with respect to the OP and the Wiki article BigDon referred to. The gas chamber was presumably operated by qualified personnel who followed strict procedure to protect themselves and avoid inflicting unnecessary pain on the condemned man with fumes other than the cyanide. They would do so with no more difficulty than I had in handling sulfuric acid in high school and college chemistry lab. I don't know what kind of school was the scene of those geysers. We strictly followed the procedure of starting with pure water and pouring the concentrated acid in very slowly while stirring with a glass rod. I did so with ease and never spilled a drop.

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    Quote Originally Posted by Hornblower View Post
    This is beside the point with respect to the OP and the Wiki article BigDon referred to. The gas chamber was presumably operated by qualified personnel who followed strict procedure to protect themselves and avoid inflicting unnecessary pain on the condemned man with fumes other than the cyanide. They would do so with no more difficulty than I had in handling sulfuric acid in high school and college chemistry lab. I don't know what kind of school was the scene of those geysers. We strictly followed the procedure of starting with pure water and pouring the concentrated acid in very slowly while stirring with a glass rod. I did so with ease and never spilled a drop.
    Anyway, you can buy pre-diluted sulphuric acid, thereby negating any risk to personnel from diluting the concentrated stuff.

    Add small molar excess of dilute sulphuric acid to KCN. Reaction goes to completion with evolution of HCN and negligible acid fumes. No complaints from the executees about acid fumes and no corrosion of the pipework and premises.

    Add a short boiling stage at the end to drive off any remaining HCN in solution or in the form of bubbles. Unlike other acids, you will not generate anything worse than steam by doing this. You are then left with a solution of potassium sulphate with a small excess of sulphuric acid to neutralise, e.g by throwing in some calcium carbonate chips.

    The resulting waste solution could probably go down the public drain with no special waste treatment measures.

    Job done.

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    Quote Originally Posted by kzb View Post
    Anyway, you can buy pre-diluted sulphuric acid, thereby negating any risk to personnel from diluting the concentrated stuff.
    Sure, but the drop they spill will concentrate as the water evaporates off and leaves strong H2SO4 behind.
    Sooner or later someone will brush a sleeve on that, or put a hand in it, with unfortunate results.
    Why not use one of the many other acids that can generate HCN from KCN, and pose no hazard of becoming highly concentrated when you spill a drop on the floor?
    It'd be safer.

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    While you all debate on how you would do it, there is a wikipedia article that describes how it was done in the US
    wikipedia
    As implemented in the United States, the gas chamber is considered to be the most dangerous, most complicated, and most expensive method of administering the death penalty.[23][24][25] The condemned person is strapped into a chair within an airtight chamber, which is then sealed. The executioner activates a mechanism which drops potassium cyanide (or sodium cyanide[26][27]) pellets into a bath of sulfuric acid beneath the chair; the ensuing chemical reaction generates lethal hydrogen cyanide gas. Because hydrogen cyanide gas condenses at approximately 78 F (26 C), the temperature in the chamber (when it is in use) is maintained at at least 80 F (27 C).[28]
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    I wonder if a chemist was involved in the initial choice of acid.
    Sulfuric is used a lot to clean calcium out of toilets, but most janitors have muriatic (HCl) on hand too.

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    If I spilled some dilute sulfuric acid, I could pour a suitable alkaline solution on it and then mop it up when it stops fizzing. Spilled concentrated acid would be more dicey, but with today's OSHA regulations there ought to be a standing procedure for it. Of course I would be wearing eye protection, especially after having had Medicare and Tricare pay for fixing my cataracts.

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    Quote Originally Posted by Squink View Post
    Sure, but the drop they spill will concentrate as the water evaporates off and leaves strong H2SO4 behind.
    Sooner or later someone will brush a sleeve on that, or put a hand in it, with unfortunate results.
    Why not use one of the many other acids that can generate HCN from KCN, and pose no hazard of becoming highly concentrated when you spill a drop on the floor?
    It'd be safer.
    Because the hazards of using sulfuric acid are negligible and easily managed compared to the hazards of a reaction to produce hydrocyanic acid gas, and the hazards and difficulties of using a volatile acid are significant. As already detailed in this thread.

    Sulfuric acid just isn't that dangerous. If someone can't handle sulfuric acid safely or clean up a spill properly, they have no business performing the reaction the acid is being used in.

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    Hi guys.

    Admittedly posting PWI. (Messed up as a soup/sandwich as the ol' Navy phrase goes. Easily getting to blah, blah, blah, nine as the BAC goes. )

    There is a plumbing product called Hotshot that is occasionally available. Concentrated sulfuric acid for opening clogged drains. I used to use it a lot. But it periodically gets banned in my state because it can be used somehow in the manufacture of explosives.

    But it sure clears out a soap and hair clog in short order.
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    Quote Originally Posted by BigDon View Post
    Hi guys.

    Admittedly posting PWI. (Messed up as a soup/sandwich as the ol' Navy phrase goes. Easily getting to blah, blah, blah, nine as the BAC goes. )

    There is a plumbing product called Hotshot that is occasionally available. Concentrated sulfuric acid for opening clogged drains. I used to use it a lot. But it periodically gets banned in my state because it can be used somehow in the manufacture of explosives.

    But it sure clears out a soap and hair clog in short order.
    I'm amazed that such things are still available to the public in the US ! Here in Britain, the cleaners at my workplace are not even allowed to use bleach anymore. And that is after the maximum concentration allowed was cut from 18% to 5% hypochlorite.

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    Quote Originally Posted by Squink View Post
    I wonder if a chemist was involved in the initial choice of acid.
    Sulfuric is used a lot to clean calcium out of toilets, but most janitors have muriatic (HCl) on hand too.
    HCl would be better for removing calcium deposits but that wasn't the question. Again I am amazed these acids are used by cleaning staff.

    I think we have some toilet cleaners in Britain that have a little HCl in the formulation but I bet the concentration is very low.

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    Quote Originally Posted by kzb View Post
    I'm amazed that such things are still available to the public in the US ! Here in Britain, the cleaners at my workplace are not even allowed to use bleach anymore. And that is after the maximum concentration allowed was cut from 18% to 5% hypochlorite.
    Were this a visual media I'd be giving you "The Tucker*" right now...

    * The Tucker is an expression of extreme incredulity combined with "Did I hear that right?" Named after newscaster Tucker Carlson, due to the effects of some of the opinions of his more extreme guests on his show.
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    Quote Originally Posted by BigDon View Post
    Were this a visual media I'd be giving you "The Tucker*" right now...
    Likewise.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    Likewise.

    Grant Hutchison
    It's correct. Using bleach is unnecessarily hazardous. Also, the concentration of bleach for sale was cut from 18% to 5% a few years back.

    Bizarrely, it is still possible to purchase caustic soda (sodium hydroxide) pellets. That one seems to have slipped through the net.

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    Chlorine bleach straight from the bottle gave me upper respiratory irritation when I used it to clean mildew from my shower without adequate ventilation.

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