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Homework Help: Trick Question? (Making a solution)

  1. Oct 3, 2008 #1
    1. The problem statement, all variables and given/known data
    A student wishes to make a 0.5 M KNO3 solution at 12 degrees C. Is this possible? Explain, and show calculations to support your answer.
    [This is a question related to a solubility lab]

    2. Relevant equations
    In my experiment, I saw that as temperature decreased and as volume increased, molarity decreased, but I don't know if temperature is actually related to this observation.

    3. The attempt at a solution
    .5 M solution = .5 moles KNO3/1L, right?
    Does temperature affect this?
  2. jcsd
  3. Oct 3, 2008 #2
    Temperature effects any ability to make any kind of solution, mainly because reactions slow down with a decrease in temperature.

    As for molarity, bond forming and other reactions take longer to occur because of the cold. You might want to look up the freezing point of KNO3 if possible.

    And to answer your question, yes. a 0.5 M solution of KNO3 means 0.5 moles per 1 L soln.
  4. Oct 3, 2008 #3


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    Science Advisor
    Homework Helper

    What's the solubility constant of KNO3 AT 12 degrees C?
  5. Oct 3, 2008 #4
    How can I calculate Ksp without having the concentrations? I know Ksp = [K+][NO3-]... would I just plug in .5 to get Ksp and go from there?
  6. Oct 4, 2008 #5
    I would think so; you have 0.5mol of KNO3 assuming 1L of solution, so that means you have 0.5mol [K+] and 0.5mol [NO3-]. This would give you a Ksp of 0.25, but then again it's been a while since I've done this.
  7. Oct 4, 2008 #6


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    Staff: Mentor

    This is pretty well soluble salt, so it will not have Kso listed. However, if you will check CRC handbook or some other, similar source, you should be able to find what is KNO3 solubility in grams per 100 g of water - check, if it is not less then 0.5M.
  8. Oct 4, 2008 #7
    Thank you all so much for your input - I now have a few different ways to look at this problem. I really appreciate it!
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