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Homework Help: Beer lambert equation and concentration

  1. Nov 21, 2005 #1
    Please help, A 15.23mg sample of cocaine was cemically digested to convert its nitorgen to ammonia and then diluted to 100.00cm3. A 10.00cm3 of this solution was placed in a 50.00cm3 volumetric flask and treated with 5.0cm3 of phenol solution and 2.0cm3 of sodium hypochlorite solution. The sample was diluted to 50.00cm3 and the absorbance at 625nm was measured using a 1cm cell using water as a reference .

    For calibration a standard solution was prepared by weighing 0.0100g of NH4CL into 1000.00cm3 flask and making up to volume with water. A 10.00cm3 aliquote of this solution was placed in a 50.00cm3 slask, treated with phenol and hypochlorite like the cocaine solution and made up to volume with water. The absorbance of this solution at 625nm was measured using a 1cm cell and water as a reference.

    absorbance readings
    Reagent blank 0.140
    NH4CL standard 0.308
    cocaine solution 0.592

    I have to calculate the % of nitrogen by mass in the cocaine!!

    Can anyone explain in sensible terms how to do the calulation, i only know that the beer lambert law equation is used A=ECL / A=ECL

    = A=C/A=C...........:cry: :cry: :cry:
  2. jcsd
  3. Nov 21, 2005 #2


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    Homework Helper

    As a general procedure, you'll need to obtain the molar absorptivity value from the standard. You can subsequently correlate the ammonium concentration values for the standard as well as the digested cocaine solution.
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