Gen.Chem: homogeneous vs heterogeneous

  1. 1. The problem statement, all variables and given/known data

    Classify each of the following as a pure substance, solution, or heterogeneous mixture:
    a) blood
    b) dry ice
    c) krypton gas
    d) a rusty nail
    e) table salt
    f) glass of lemonade

    Justify your answers.

    2. Relevant equations
    No equations obviously...


    3. The attempt at a solution

    Here's what I figure...but I'm not sure!!!

    a) blood - no idea...
    b) dry ice - pure substance (why???)
    c) krypton gas - pure substance (single element)
    d) rusty nail - heterogeneous mixture (rust is produced by oxidizing the iron)
    e) table salt - solution (homogeneous mixture of Na and Cl atoms)
    f) glass of lemonade - solution?? (I'm not sure because my book said milk is heterogeneous but coffee is a solution)

    Yeah...so if you know, help me out! And if my justifications aren't right, please let me know that too :)

    Thanks to all.
     
  2. jcsd
  3. Heterogeneous mixtures can be mechanically separated from each other, so with blood, consider what happens when you put a test tube of blood in a centrifuge.
     
  4. Yeah, I finally came to that conclusion last night...blood is heterogeneous. But what about dry ice- is it considered a pure substance even though it's frozen carbon dioxide, or is it a solution of carbon and oxygen atoms??
     
  5. "Classify each of the following as a pure substance, solution, or heterogeneous mixture:"

    Are you sure this is the full question because I actually think blood is homogeneous. I may be wrong though.
     
  6. Yeah, it's the full question. I asked a chem major about it and they said blood is heterogeneous because the blood cells can be separated from the plasma. That made sense to me...
     
  7. a) heteromix
    b) dry ice = google this, it will give you a chemical formula
    c) correct
    d) yes, hetero mix if the nail is not rusted all the way through and there is some iron underneath
    e) NOT a solution. NaCl is NOT a mixture
    f) solution or hetero mix : depends on if there is pulp in it or not
     
  8. Well I asked my chem lab professor about the blood question. She said it is homogeneous. Her explantion was blood is the same throughout. Salt water is homogeneous and can also be seperated, for example evaporation.
     
  9. chemisttree

    chemisttree 3,721
    Science Advisor
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    Hmmmmm.... If your chem lab teacher was really a professor (probably not) I'd demand to see proof of the PhD. That's one doctor whose information I'd always get second opinions for...
     
  10. I'm sure questioning my profs credentials would really help my GPA. I am curious, why do you say blood is not homogeneous? It does have a uniform composition. Asking because I am now confused.
     
  11. Considering a definition:Homogeneous matter has a definite composition and properties and any amount of it has the same composition and properties. It may be a mixture, such as brass, or elemental, like pure iron. Heterogeneous matter, such as granite, does not have a definite composition.Homogeneous matter has a definite composition.

    A WBC count test for 4,500-10,000 white blood cells/mcL (cells per microliter) This would imply an expected uniformity in blood.
     
  12. chemisttree

    chemisttree 3,721
    Science Advisor
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    Gold Member

    Whole blood contains both serum and blood cells (erythrocytes). Upon standing it will coagulate unless it is treated with an anticoagulant. When it is treated with anticoagulant, it manifests a property called the erythrocyte sedimentation rate. Can this be a homogenous mixture if it settles upon standing?
     
  13. You make a good point and I do not wish to beat a dead horse, as this thread might become. I will capitulate to you, however, one final comment; blood in it's normal state is in a circulatory system and an anticoagulant is not a natural part of blood, nor is blood free standing in which case I could argue your point. Allowing blood to settle could be considered a mechanical means of separation. I think this is all symantics, but after all I did have to try and defend my professor.

    Cheers and Peace :)
     
  14. chem

    a) blood - mixture homogeneous
    b) dry ice - not sure
    c) krypton gas - pure substance element
    d) rusty nail - heterogeneous mixture
    e) table salt - pure subtance , compound of Na and Cl atoms
    f) glass of lemonade - mixture homogeneous
     
  15. Blood is definitely a heterogeneous mixture because it is a colloid. It is made up of different microscopic material that does not occur uniformly throughout; therefore, it is not homogeneous.

    Dry ice is a pure substance because it is made of a single compound.

    You are right about krypton gas and the rusty nail.

    Table salt, like dry ice, is a pure substance because it is made of a single compound, NaCl.

    Finally, the glass of lemonade is a solution if there is no pulp in it because the sugars and citric acid dissolve into the water.
     
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