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Homework Help: Moles of ions in aqueous solution

  1. Oct 1, 2006 #1
    How many moles and numbers of ions of each type are present in the following aqueous solutions?

    3.26 L of a solution containing 6.96 x 10^21 formula units of lithium nitrate per liter

    I got 1.16e-2 mols of Li and NO3 as well as 6.99e21 ions for each. The software I am using (webassign) says it is incorrect. What am I doing wrong?

    First, I found the number of moles of the total was 1.16e-2 moles. Since the two ions are in a 1:1 ratio, should they not be the same as the total? Or am I supposed to use the 3.26L in there somewhere?

    EDIT: I found what I did wrong. I didn't see the per liter at the end
    Last edited: Oct 1, 2006
  2. jcsd
  3. Oct 1, 2006 #2
    3.26 L = 3.26 [tex]dm^3[/tex]

    There is approx [tex]6.02 \times10^{23}[/tex] "formula units" in a mole

    [tex]\frac{6.96 \times10^{21}}{6.02 \times10^{23}}[/tex]

    [tex]\frac{6.96}{6.02} \times 10^{21-23}[/tex]

    [tex]1.16 \times 10^{-2}[/tex] moles

    [tex][LiNO_{3}] = \frac{1.16\times10^{-2}}{3.26} mol dm^{-3}[/tex]

    Is the answer ~ 0.003?

    Do you have to take dissociation constant into account?
    Last edited: Oct 1, 2006
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