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Review Questions

  1. Jun 17, 2004 #1
    Doing a review for exams but some word type questions I dont understand, and another question thats not word type.

    Anybody that can answer please do, I do need to know to do it by Friday morning.

    Here they are...

    Question 1....

    An industrial plant is confronted with a problem of seperating the metal ions found in a large vat of solution. By analysis, the solution was found to contain varying quanties of silver, barium and Iron(III) ions. Suggest a procedure for seperating the metal ions by precipitation.

    Question 2....

    Fertilizer is used to replace depleted nutrients in soil. Liquid ammonia and ammonium nitrate are used to replace needed nitrogen in the soil. Based on the percentage of nitrogen by mass, which of these would be better fertilizers ? Assume cost is the same (per kilogram).

    and one number question:

    A chemist wishes to preare 200ml of a saturated solution of BaF2, the concentration of which is 6.3 * 10-3mol/L. Determine the mass of BaF2 that will be needed to make up the 200mL of solution.
  2. jcsd
  3. Jun 17, 2004 #2


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    1) Add HCl to precipitate the Silver ans AgCl, filter out the rest (Barium + Iron)
    Add H2SO4, the Iron dissolves but BaSO4 forms a precipitate. Filter again, and you're left with only the Iron.

    2) Calculate the molar masses of NH3 and NH4NO3. The first contains 1 mole (14g) of nitrogen while the second contains 2 moles (28 g) of nitrogen. Which has a greater fraction of nitrogen ?

    3) Find the number of moles of BaF2 in the solution by multiplying concentration with volume (why is this true ?). Multiply this by the molecular weight (or molar mass) to get the weight.
  4. Jun 17, 2004 #3


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    Question 1 is kind of tough.

    You want to introduce an ion (or ions) which will react with the metal ions to form an insoluble substance. So, you need to look at your periodic table and figure out which ions the metal will form an ionic bond with. The resulting compound has to be insoluble if you're removing the ions by precipitation - you should have a chart explaining how to determine if a compound is soluble or insoluble.

    The tough part is that just saying you're going to insert the ions probably isn't enough. You need to introduce a substance in which the metal ions will replace one of the elements of the compound you put into the solution, which means you'll now have a different ion in the substance. So you it's going to take a bit of thought to set up a string of reactions which will eventually remove all of the ions.

    Question 2 is just a matter of figuring out which has the most nitrogen. You figure this out by using the molar mass of each and determining which has the most nitrogen per kilogram

    Question 3 - concentration is in moles per liter. You figure out the number of moles of the BaF2 by multiplying the concentration by the volume. Once you have the number of moles, you determine the mass by multiplying by the molar mass.
    Last edited: Jun 17, 2004
  5. Jun 17, 2004 #4
    Thanks for the quick responses guys. Great explanations BTW, had no problems figuring out #2 and #3. I do have issues understading #1, so if one of you could show the work on how you got to that, be great.
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