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Concentration problem

  1. Oct 13, 2007 #1
    Assume the human eye can detect light with transmittance of 0.35.
    The colored form of the indicator has ε = 8.79 x 10^5. and λmax = 580 nm. How
    much indicator in ml should be used if the indicator has concentration 0.1% w/w in water.

    Equation Used:
    Beer's Law = A = εbc
    where ε is given as 8.79 x 10^5
    b = 1.00cm
    A= -logT = -log(0.35) = 0.456

    Using Beer's Law, I solved for C and got 5.08(10^-7)mol/L
    But I don't know what to do to find the amount of indicator needed.
    The molecular formula is C15H6N4 if that helps.
  2. jcsd
  3. Oct 15, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Looks like you are going to need 5.08 X 10^-7 moles per liter to see it. How much of the 0.1% w/w of the indicator (you should probably convert this to mol/L using the molecular formula) will you need?

    That depends on how much solution you will have to dilute this into (what is the volume of the cell). This information is missing in your problem.
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