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Water / alkanes mix

  1. Apr 22, 2009 #1
    Water / alkanes "mix"

    Ok, so I had a chemistry exam today an missed one of the questions:

    Q: What prevents you from being able to mix an alkane with water?

    My original thought was that they cannot mix because water is polar, and alkanes are non polar....but then I started to think about the word "mix" that the professor used on the exam.

    Polarity would certainly prevent the alkane from being soluble in water, but in the case of a heterogeneous mixture, density would play a part in the "mixing". For example, if you had a heterogeneous mixture of plastic and lead beads in a bucket which are evenly spaced, and you agitate the mixture, the beads will separate themselves out of the mixture and form two different layers.

    So basically, because the professor used the word "mix" instead of "dissolve", it caused me to write down difference in density instead of polarity.

    The professor's answer was polarity.

    Do you think I will be able to argue this one to get a point back on my exam score?

    Last edited: Apr 22, 2009
  2. jcsd
  3. Apr 23, 2009 #2


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    Staff: Mentor

    Re: Water / alkanes "mix"

    My English fails me here. Does mix means 'preparing a homogenous mixture'?

    In Polish you can 'mix' things, but they don't have to be 'mixed' afterwards (ie they can still separate). So nothing stops your from mixing, but properties stops you from preparing a homogenous mixture. If that's the case in English also, question is poorly worded.
  4. Apr 23, 2009 #3
    Re: Water / alkanes "mix"

    Exactly. That was the problem I was having while taking the exam. The professor used the word "mix", which doesnt mean she was referring to a homogeneous mixture, just that the substances were attempted to be mixed, which lead me to answer with difference in density instead of polarity.
  5. Apr 23, 2009 #4


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    Staff: Mentor

    Re: Water / alkanes "mix"

    If the question is poorly worded, you should try to discuss it with her.
  6. Apr 23, 2009 #5
    Re: Water / alkanes "mix"

    Anyway, a density difference does not prevent a "mixing", either if is intended as solution or as suspension.
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