You dissolve a compound with a molecular mass of 262.54 in a 10-mL volumetric fl

Question

You dissolve a compound with a molecular mass of 262.54 in a 10-mL volumetric flask. You remove a 1.00-mL aliquot, place it in a 25-mL volumetric flask and dilute it to the mark. The absorbance of this diluted solution at 343 nm was 0.483 in a 1.000-cm cuvet. The molar absorptivity for this compound at 343 nm is E343 = 6023 M^-1cm^-1. (a) What is the concentration of the compound in the cuvet? (b) What is the concentration of the compound in the 10-mL flask? (c) How many milligrams of compound were used to make the 10-mL solution?

Explanation / Answer

Say compound P has moleular mass is = 262.54

You need to Beer's law to calculate the concentration.
A = mCl (A=absorbance, m = molar extinction coefficient, C = concentration, l=path length of 1 cm)

A=0.483 , m=6023 M1cm1 l= 1cm

If we put above values in the equation

A = mCl

0.483=6023 x C x 1

C=0.000080 Mol/L

N1V1=N2V2

N1 X 1ml= 0.00008 X 25ml =0.002 Mol/L in 1 ml and for 10 ml 0.02 Mol/L

3. 10 ml solution contain 0.02 mol of compound of molecular mass 262.54

0.02 x 262.54=5.2 gmmeans 5200mg

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