You dissolve a compound with a molecular mass of 289.49 in a 10-mL volumetric fl

Question

You dissolve a compound with a molecular mass of 289.49 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 341 nm was 0.444 in a 1.000-cm cuvet. The molar absorptivity for this compound at 341 nm is 341 = 6117 M–1 cm–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

Answer – Given, molar mass of compound 289.49 g/mol, volume = 10.0 mL

Length, l = 1.0 cm , volume of solution = 1.0 mL and diluted to 25 mL

Absorbance , A = 0.444 , molar absorptivity =6117 M-1.cm-1

a) We know formula for Beer-Lambert law

A = *l*C

0.444 = 6117 M-1.cm-1 * 1.0 cm * C

So, C = 0.444 / 6117 M-1.cm-1 *1.0 cm

           = 7.26*10-5 M

The concentration of the compound in the cuvet is 7.26*10-5 M

b) Concentration of the compound in the 10-mL flask

We calculate concentration of solution of 25 mL is 7.26*10-5 M

So using the dilution law

M1V1 = M2V2

So, M2 = M1V1/V2

             = 7.26*10-5 M *25 mL/ 10 mL

              = 1.81*10-4 M

Concentration of the compound in the 10-mL flask is 1.81*10-4 M

c) So, moles of compound = 1.81*10-4 M * 0.010 mL

                                       = 0.00181 moles

So mass of compound = 0.00181 moles * 289.49 g/mol

                                    = 0.525 g

So, 1 g = 1000 mg

So, 0.525 g = ?

= 525 mg

So, 525 milligrams of compound were used to make the 10-mL solution.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.