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Homework Help: Some chemistry questions

  1. Jun 12, 2005 #1
    I'm just having some trouble answering a few of these questions.

    1.Calculate the molar activity of 3H (tritium) (in curie), given it's half life is 12.26 years.

    My calculations=

    T(1/2) = ln2/Y (where Y=decay rate)

    Y=ln2/(12.26*365*24*60*60) = 1.79*10^-9

    Molar activity= Y*6.022*10^23 = 1.08*10^15

    In curie = (1.08*10^15)/(3.70*10^10)

    = 2.92*10^4 curie

    The answer according to the solutions is 2.916*10^3 curie/mol. I'm pretty sure I'm right, but I just wanted to get it checked. The question states its meant to be answered in curie, not curie/mol anyway.

    2. The energy associated with one photon of light when an electron drops from it's first excited state back to it's ground state is 3.37*10^-19 J.

    The ionisation energy of ground state sodium is 8.34*10^-19 J per atom. Calculate the enegy required to ionise the 3p electron of an excited sodium atom. Give your answer in kJ/mol.

    3. A saturated solution of iodine in water contains 0.330g I2 per litre, but more than this amount can dissolve in a potassium iodide soltion because of the following equilibrium.

    I-(aq) + I2(aq) <---> I3-(aq)

    A 0.100 M KI solution dissolves 12.5g of I2 per litre, most of which is converted to I3-(aq). Assuming that the concentration of I2(aq) in all saturated solutions is the same, calculate the equilibrium constant for the above reaction.

    Any help would be appreciated. :smile:

  2. jcsd
  3. Jun 12, 2005 #2


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    The first looks okay to me.For the second,i'd do a diagram with the 3 energy levels involved,if i were you...

  4. Jun 12, 2005 #3
    Ok. Thanks for that. That really helped me. I didn't think diagrams were usually that helpful. :smile:
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