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Hydrochloric Acid on Concrete

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  1. #1
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    Default Hydrochloric Acid on Concrete

    Hi all,
    A simple one for you guys who can remember your chemistry.
    What is the gas or what do the fumes contain when in the process of acid etching concrete with hydrochlric acid (muriatic acid)?
    Cheers
    Bill

  2. #2
    A Member of the Holy Trinity silentC's Avatar
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    Hydrogen chloride?
    "I don't practice what I preach because I'm not the kind of person I'm preaching to."

  3. #3
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    Gas produced would probably be hydrogen, but fumes would certainly include HCl, and chlorine.
    Alastair

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    Dances with splinters Skew ChiDAMN!!'s Avatar
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    Going by my vague memories of high-school chem, I agree with Alistair: I'm pretty sure that it's only Hydrogen gas generated by the HCl reacting with the hydrated lime and any AlOxides.

    There'd also be HCl fumes, but that's not from any reaction - you'd have the same amount of fumes if you poured HCl over a completely inert surface. It's never a good idea to sniff acid.

    Chlorine could be generated from reactions with impurities in the conc, but would be so small as not to be a concern... I'd be more worried about a whiff of HCl fumes.
    I may be weird, but I'm saving up to become eccentric.

  5. #5
    Lumberlubber Bleedin Thumb's Avatar
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    I think it goes like this

    3 HCL + Ca(OH2) = H2 + CaCL2 + CL + H20
    So by my reconing its hydrogen and Chlorine gas given off. It been a long time though so I may be way off.

    EDIT just realised my Hydrogen doesn't add up. By changing the CL to HCL the equation does balance so I take it back about Chlorine gas.

    Actually I'm not sure that Hydrochloric acid is what it is called.... maybe it actually should be called Hypochloric acid as I think HCL should be a gas?????? geeze it has been a long time...
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  6. #6
    Dances with splinters Skew ChiDAMN!!'s Avatar
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    Hydrochloric Acid is right - Hypochloric Acid is HClO

    ...and Chlorine gas is diatomic (Cl2)

    I used to love chem, but hated the damned equations... gimme a handful of nitropills and a bucket of dieseline any time!
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  7. #7
    Lumberlubber Bleedin Thumb's Avatar
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    But Skew isn't HCL a gas and when you combine it with water it disassociates to form HClO?


    Edit No dont answer that I'm wrong but is my equation correct

    3HCL + Ca(OH)2 = H2 + CaCL2 + HCL + H2O


    PS how do you do those small 2's
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  8. #8
    Dances with splinters Skew ChiDAMN!!'s Avatar
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    Pure HCL is a gas... but Hydrochloric acid is a solution of the gas suspended in good ol' water.

    Quote Originally Posted by Bleedin Thumb View Post
    Edit No dont answer that I'm wrong but is my equation correct

    3HCL + Ca(OH)2 = H2 + CaCL2 + HCL + H2O
    My high school teacher wouldn't pass it. (Although to all practical intents and purposes ya got it right.) For starters, you have HCl on both sides, obviously one of the HCl's on the left isn't doing anything in the equation... so you can simplify it to

    2HCl + Ca(OH)2 = H2 + CaCl2 + H2O

    That looks right to me and it balances out but, like you, it has been a long time since I've broken out a chemistry book.

    PS how do you do those small 2's
    I cheated and just used the font size button at the top of the editor to use a size 1 font.
    I may be weird, but I'm saving up to become eccentric.

  9. #9
    Golden Member mic-d's Avatar
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    Nope, you're all wrong!
    I'll give you a hint - it's a greenhouse gas!

    Cheers
    Michael

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    Dances with splinters Skew ChiDAMN!!'s Avatar
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    Ain't CO2 or Methane (CH4) as there's no carbon in HCl or concrete.

    Hmmm... water vapour can be considered a greenhouse gas, but we already covered that. What else is there? Nitrous Oxide (NO2) and Ozone (O3)? Don't seem right. And I'm sure that chlorofluorocarbons, hydrofluorocarbons and perfluorocarbons aren't in the running.

    Now you have me wondering. What do we win if we guess right?
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  11. #11
    Golden Member mic-d's Avatar
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    Quote Originally Posted by Skew ChiDAMN!! View Post


    Ain't CO2 or Methane (CH4) as there's no carbon in HCl or concrete.

    Hmmm... water vapour can be considered a greenhouse gas, but we already covered that. What else is there? Nitrous Oxide (NO2) and Ozone (O3)? Don't seem right.

    Now you have me wondering. What do we win if we guess right?
    Lots of carbon in concrete.
    (if it's the mafia type )

    try again
    CHeers
    Michael

  12. #12
    Dances with splinters Skew ChiDAMN!!'s Avatar
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    Quote Originally Posted by mic-d View Post
    Lots of carbon in concrete.
    Huh?

    AFAIK, sand's primarily a silica, cement is a mixture of aluminium, calcium, iron and silica, then there's the gravel (usually a basalt), water and colouring - which are usually, I think, Al- or FeOxides.

    I'm pretty sure modern conc doesn't include ash any more? Maybe in the hardeners in use now? But I thought they was CaCL based. Hmmm...

    Mind you, I'm just making educated guesses here. I give up. My brain hurts.
    I may be weird, but I'm saving up to become eccentric.

  13. #13
    Lumberlubber Bleedin Thumb's Avatar
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    Lots of carbon...as in CaCo3 + HCL = CaCl + H2Co3????


    Mate its Friday arvo give us a break!
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    Dances with splinters Skew ChiDAMN!!'s Avatar
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    D'OH! And I mentioned basalt...

    try: CaCO3 + HCl = CaCl + H2O + CO2

    ... no... hang on... that doesn't balance. But along those lines...
    I may be weird, but I'm saving up to become eccentric.

  15. #15
    Lumberlubber Bleedin Thumb's Avatar
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    No way that is too simple must be wrong
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  16. #16
    Dances with splinters Skew ChiDAMN!!'s Avatar
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    It's wrong. It should be CaCl2 not CaCl... and that really don't balance
    I may be weird, but I'm saving up to become eccentric.

  17. #17
    Lumberlubber Bleedin Thumb's Avatar
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    I really was under the impression that H2 was released.
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  18. #18
    Dances with splinters Skew ChiDAMN!!'s Avatar
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    It is. The first reaction we talked about would be happening too. (I think.)

    But I guess that half the H2 it generates would react with the second reaction's O2 to create H2O, so more CO2 is realeased to air than H2

    Did I mention that I'm really glad I don't do this for a living? I'd be sacked only a couple of hours into the job.
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  19. #19
    Lumberlubber Bleedin Thumb's Avatar
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    Yeah, from memory this would have been first year high school chemistry!
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  20. #20
    Dances with splinters Skew ChiDAMN!!'s Avatar
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    Now that I think on it, I vaguely recall an attempt at anenvironment in a sealed dome (an experiment in closed system ecologies) that failed because significant amounts of O2 were disappearing and they couldn't balance the eco-system. Apparently 'twas all due to the foundation cement curing and releasing CO2.

    Or something like that...
    I may be weird, but I'm saving up to become eccentric.

  21. #21
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    Thanks Guys,
    I was expecting a fairly simple answer, I suspected chlorine gas might have been in it.
    I think I'll restrict myself to saying that a highly toxic gas is given off and not get any more detailed.

    Cheers
    Bill

  22. #22
    That's SIR!!......Not CUR Ivan in Oz's Avatar
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    Lightbulb

    Quote Originally Posted by Skew ChiDAMN!! View Post
    ... gimme a handful of nitropills and a bucket of dieseline any time!
    Nah!

    Open bucket of Pool Chlorine and a leaky container of Brake Fluid
    Now at opposite ends of the shed

    YES!!!
    There is still Fly Ash in concrete
    Navvi

  23. #23
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    As a geologist myself, I'd be willing to bet most gas given off would be CO2. Colourless and odourless.

    You'd smell it if any chlorine gas was given off - given my uni-level chem is getting a tad old, I'd say the chlorine would prefer to bind up as CACl2 (common kettle-scale), as its easier to form the CaCL2 ionic bond over the higher energy Cl2 gas covalent bond. Which leaves the H to bind with any free CO3 carbonate in the concrete, which'd produce water and CO2.

    Many of the rocks where I work (a lead mine) are very lime-rich and fizz rather vigorously when acid is applied! We have a funky test where we let the acid sit for 30 seconds or so, then spray the rock with potassium iodide (KI). Lead in the rock freed up by the acid grabs the iodine and goes brilliant yellow (the old yellow paint dye colour). Can be very strong sometimes where the rock is up to 40% lead by weight!

    Cool.
    Rick Burlow

  24. #24
    1K Club Member Pulse's Avatar
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    http://www.ceramics-silikaty.cz/2000...000_03_114.pdf

    After reading this I don't feel much wiser...

    It's not Hydrogen.. thats HCl and metal

    reactions with hydroxide should leave a salt and water...

    CO2 is probably most likely

    Pulse

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