Question

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.

Answer 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