You dissolve a compound with a molecular mass of 287.57 g/mol 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 349 nm was 0.486 in a 1.000-cm cuvet. The molar absorptivity for this compound at 349 nm is ε349 = 5911 M–1 cm–1.
a) using the Beer's law which says,
absorbance =lC
where = molar absortivity constant = 5911/ (M.cm)
l = length of cuvet = 1cm
C = Concentration of solution in cuvet
therefore, Concentration
b) using the dilution equation we know that
M1V1 = M2V2
where M1
V1 = 25 mL
V2 = 10mL
hence , M2 = Conentration of compound in 10mL flask
c) using the Concentration calculated we can find the no. of moles as
therefore, no. of moles = molarity (Concentration) X Volume of solution in L
X 0.01 L
=
now, mass of the compund = no. of moles X molecular mass of the compound
= X 287.57 g/mol
=
= 0.59095 mg
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