A is correct, but B and C are incorrect. You dissolve a compound with a molecula

Question

A is correct, but B and C are incorrect. You dissolve a compound with a molecular mass of 283.45 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 347 nm was 0.533 in a 1.000-cm cuvet. The molar absorptivity for this compound at 347 nm is epsilon_347 = 5645 M^-1 cm^-1 What is the concentration of the compound in the cuvet What is the concentration of the compound in the 10-mL flask How many milligrams of compound were used to make the 10-mL solution

Explanation / Answer

we know that

according to Beers law

A = e x l x c

where

A = absorbance

e = absorptivity

l = path length

c = concentration

now

for compound in the cuvet

0.533 = 5645 x 1 x c

c = 9.44 x 10-5

so

a)

concentraton of the compound in the cuvet is 9.44 x 10-5 M

b)

now

diluted solution in the cuvet is 25 ml

we know that

moles = conc x volume (L)

so

moles of compound in the cuvet = 9.44 x 10-5 x 25 x 10-3

moles of compound in the cuvet = 2.36 x 10-6

now

this moles of compound came from the 1 ml aliquot

so

conc of this 1 ml aliqout = moles / volume (L)

= 2.36 x 10-6 / 1 x 10-3

= 2.36 x 10-3

so

conc of this 1 ml aliqout = 2.36 x 10-3 M

As this 1 ml is taken from the 10 ml volumetric flask

both the conc should be same

so

concentration of the compound in the 10-ml flask is 2.36 x 10-3 M

c)

now

for the 10 ml flask

moles = conc x volume (L)

moles of compound = 2.36 x 10-3 x 10 x 10-3

moles of compound = 2.36 x 10-5

now

mass = moles xmolar mass

so

mass of compound = 2.36 x 10-5 x 283.45

mass of compound = 6.69 x 10-3 g

so

mass of the compound is 6.69 mg

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

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