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General Chemistry Questions (Solubility)

  1. Oct 2, 2005 #1
    Please help me with the following problems.

    1.)(85) A 55-g sample of a geseous fuel mixture contains 0.51 fraction propane C3H8; the remainder is butane. What are masses of propane and butane in sample?

    Using the formula: Ax = n(solute)/n(total), i initially solved for total moles. I went about this by multiplying 7 by the molar mass of carbon (there is a total of 7 carbons) and similarly, 18 by the molar mass of hydrogen. This allows me to solve for moles of solute, which i then convert into mass. However, i get an answer of 12.1g and 43.0 g, which differs from the book.

    2.) (105) A solution has 0.375 mol Na2CO3, 0.125 mol Ca(NO3)2, and 0.200 mol AgNO3 in 2.0 L of water. Write balanced reactions and calculate molarities of each ion.

    I noticed that NO3(-1) is always soluble. CO3(2-) can form solids with Ca+ and Ag+. So i wrote two seperate reactions, one in which CaCO3 was the solid, and the other in which Ag2CO3 was the solid. This allowed me to get the moles of Na+, which i then converted into molarity. But I'm not sure this is the correct way of approaching this question.


    Thank you.
     
  2. jcsd
  3. Oct 2, 2005 #2
    Anyone ?




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  4. Oct 3, 2005 #3

    GCT

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    I'm not quite sure what you're going for here. When they refer to fraction, are they referring to mole fraction or mass fraction?

    it'll depend on which has the higher Ksp, the less soluble salt will precipitate almost exclusively, but in this case you have enough carbonate ions to precipitate both Ag and Ca, you'll just need to determine, the amount of carbonate left over, if any, remembering that 2 Ag+ is required for every carbonate...all of this assuming that both of the precipitates involving silver and calcium are completely insoluble (which is what your teacher probably wants).


    the molarity of Na+ is simply 2 x .375/2.0L.

    assuming that all of Ag and Ca precipitate, which you'll need to figure out, all that's left is to find the moles of carbonate remaining in solution. Of course you'll need to add up all of the moles of nitrate and divide by volume to find its molarity.
     
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