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Stupid Question about Hetero/Homogeneous mixtures

  1. Feb 1, 2008 #1
    I was just asked "Are salt and sand heterogeneous or homogenous mixtures?" I can see that sand is heterogeneous, but why is salt heterogeous?

    Casey
     
  2. jcsd
  3. Feb 3, 2008 #2
    i normally think of heterogeneous and homogeneous this way

    homogenous: think of it as 2 boys (same gender)

    heterogeneous: boy and girl (different genders)

    plz dont laugh lol

    so salt is heterogeneous cause u see different particles (color wise w.e.)

    but salt, its all the same white crystals or w.e. so thay makes it heterogeneous

    ya this isnt the greatest explanation chemistry wise but it helps me remember!

    hope it helped bud :-)
     
  4. Feb 3, 2008 #3

    I think you mixed up something.. . . I can't make heads or tails of your explanation. Thanks though!
     
  5. Feb 3, 2008 #4
    Salt isn't a mixture, it's a compound.
     
  6. Feb 3, 2008 #5
    Well, the book wants to know if salt is homogeneous or heterogeneous.
     
  7. Feb 3, 2008 #6
    Oh, well then I'd guess heterogeneous because the sodium and chloride ions occupy distinct areas (and thus distinct properties) within the packing structure of a salt crystal.
     
  8. Feb 3, 2008 #7
    Interesting. I think that answers it then. It was a question in my girlfriends text and they said the answer was heterogeneous too. . . but I just couldn't see why and it was driving me nuts! Thanks
     
  9. Feb 4, 2008 #8
    The question is if sand, or salt is a homogeneous/heterogeneous mixture? About salt, If he intended "grains of salt mixed with air", then it's a heterogeneous mix, but if you consider a single grain it's not a mix at all since it's a pure compound. In general, when you have 2 or more different compounds (and so a mix), the mix is homogeneous if it's formed by a single phase and so is a solution, heterogeneous if two or more phases. Ex: water and oil forms two separate phases (even when one of them is finely emulsionated into the other); water and alcohol instead forms an only phase (homogeneous mix) because they forms a solution.
    About sand...i live the answer to you.
     
  10. Feb 4, 2008 #9

    Andy Resnick

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    I would say pure salt is a homogeneous substance. No matter how much of it you have, you have equal amounts of Na and Cl. There are well-defined intensive quantities (density and specific heat, for example) that do not vary depending on where you took a small sample of salt.
     
  11. Feb 5, 2008 #10
    It doesn't matter if you have equal amounts of Na and Cl; in other compounds (e.g. water) you don't have but they are still homogeneous (NON mixtures); every pure compound in one only phase is homogeneous.
     
  12. Feb 5, 2008 #11

    Andy Resnick

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    Well, yes.. but that's not what I meant. In any homogeneous compound, regardless of how much you have, you retain the stoichiometric ratio of the components. This is not true for things like sand or concrete.
     
  13. Feb 6, 2008 #12
    A piece of solid brass is homogeneous or not, for you?
     
  14. Feb 6, 2008 #13

    Andy Resnick

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    That's an interesting question. I would say macroscopically it is homogeneous. I don't know enough about the microscopic structure to say anything else. Steel compounds (cementite, austentite, etc) are heterogeneous on a microscopic scale.
     
  15. Feb 6, 2008 #14
    Brass is an example of alloy which is a solid solution (with one phase only if Zn concentration is less than 37%) so it's homogeneous, but it doesn't have a specific composition.
     
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