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Homework Help: Concentration problem using absorbance

  1. Nov 25, 2012 #1
    1. The problem statement, all variables and given/known data

    Hi. A patient produced 1122 mL of urine in 24 hours.
    A 1.00-mL aliquot of the sample was treated with
    Mo(Vl) and ascorbic acid and was diluted to a
    volume of 50.00 mL. A calibration curve was pre-
    pared by treating 1.00-mL aliquots of phosphate
    standard solutions in the same manner as the urine
    sample. The absorbances of the standards and the
    urine sample were obtained at 650 nm, and then
    concentration of 1.00ml diluted aliquots of phosphate is found 2.5ppm.

    What mass in grams of phosphorus was eliminated per day by the patient?

    What is the concentration of phosphate in the urine (mmol/L)?

    2. Relevant equations

    A = abC

    3. The attempt at a solution

    Ok, what I really don't get is why in the first question they ask me for PHOSPHOROUS and in the second one for PHOSPHATE. And again, in the problem it says that this is a method used to determine PHOSPHOROUS, yet the standards are made of PHOSPHATE.

    It's really confusing to me... they shouldn't be the same thing, right?
  2. jcsd
  3. Nov 25, 2012 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Phosphate contains phosphorus - one atom per molecule.
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